Change let into const (#457)

This patch:
- changes `let` into `const` throughout codebase
- adds eslint check to prefer const over let

.eslintrc.js

@@ -47,6 +47,7 @@ module.exports = {
         "new-parens": 2,
         "func-call-spacing": 2,
         "arrow-parens": [2, "as-needed"],
+        "prefer-const": 2,
 
         // anti-patterns
         "no-var": 2,

DeviceDescriptors.js

@@ -628,5 +628,5 @@ module.exports = [
     }
   }
 ];
-for (let device of module.exports)
+for (const device of module.exports)
   module.exports[device.name] = device;

install.js

@@ -24,7 +24,7 @@ const revisionInfo = Downloader.revisionInfo(platform, revision);
 if (revisionInfo.downloaded)
   return;
 
-let allRevisions = Downloader.downloadedRevisions();
+const allRevisions = Downloader.downloadedRevisions();
 Downloader.downloadRevision(platform, revision, onProgress)
     // Remove previous chromium revisions.
     .then(() => Promise.all(allRevisions.map(({platform, revision}) => Downloader.removeRevision(platform, revision))))
@@ -52,7 +52,7 @@ function onProgress(bytesTotal, delta) {
 }
 
 function toMegabytes(bytes) {
-  let mb = bytes / 1024 / 1024;
+  const mb = bytes / 1024 / 1024;
   return `${Math.round(mb * 10) / 10} Mb`;
 }
 

lib/Browser.js

@@ -50,7 +50,7 @@ class Browser {
    * @return {!Promise<string>}
    */
   async version() {
-    let version = await this._connection.send('Browser.getVersion');
+    const version = await this._connection.send('Browser.getVersion');
     return version.product;
   }
 

lib/Connection.js

@@ -27,7 +27,7 @@ class Connection extends EventEmitter {
    */
   static async create(url, delay = 0) {
     return new Promise((resolve, reject) => {
-      let ws = new WebSocket(url, { perMessageDeflate: false });
+      const ws = new WebSocket(url, { perMessageDeflate: false });
       ws.on('open', () => resolve(new Connection(url, ws, delay)));
       ws.on('error', reject);
     });
@@ -66,8 +66,8 @@ class Connection extends EventEmitter {
    * @return {!Promise<?Object>}
    */
   send(method, params = {}) {
-    let id = ++this._lastId;
+    const id = ++this._lastId;
-    let message = JSON.stringify({id, method, params});
+    const message = JSON.stringify({id, method, params});
     debugProtocol('SEND ► ' + message);
     this._ws.send(message);
     return new Promise((resolve, reject) => {
@@ -82,9 +82,9 @@ class Connection extends EventEmitter {
     if (this._delay)
       await new Promise(f => setTimeout(f, this._delay));
     debugProtocol('◀ RECV ' + message);
-    let object = JSON.parse(message);
+    const object = JSON.parse(message);
     if (object.id && this._callbacks.has(object.id)) {
-      let callback = this._callbacks.get(object.id);
+      const callback = this._callbacks.get(object.id);
       this._callbacks.delete(object.id);
       if (object.error)
         callback.reject(new Error(`Protocol error (${callback.method}): ${object.error.message} ${object.error.data}`));
@@ -109,10 +109,10 @@ class Connection extends EventEmitter {
 
   _onClose() {
     this._ws.removeAllListeners();
-    for (let callback of this._callbacks.values())
+    for (const callback of this._callbacks.values())
       callback.reject(new Error(`Protocol error (${callback.method}): Target closed.`));
     this._callbacks.clear();
-    for (let session of this._sessions.values())
+    for (const session of this._sessions.values())
       session._onClosed();
     this._sessions.clear();
   }
@@ -168,14 +168,14 @@ class Session extends EventEmitter {
   send(method, params = {}) {
     if (!this._connection)
       return Promise.reject(new Error(`Protocol error (${method}): Session closed. Most likely the page has been closed.`));
-    let id = ++this._lastId;
+    const id = ++this._lastId;
-    let message = JSON.stringify({id, method, params});
+    const message = JSON.stringify({id, method, params});
     debugSession('SEND ► ' + message);
     this._connection.send('Target.sendMessageToTarget', {sessionId: this._sessionId, message}).catch(e => {
       // The response from target might have been already dispatched.
       if (!this._callbacks.has(id))
         return;
-      let callback = this._callbacks.get(id);
+      const callback = this._callbacks.get(id);
       this._callbacks.delete(object.id);
       callback.reject(e);
     });
@@ -189,9 +189,9 @@ class Session extends EventEmitter {
    */
   _onMessage(message) {
     debugSession('◀ RECV ' + message);
-    let object = JSON.parse(message);
+    const object = JSON.parse(message);
     if (object.id && this._callbacks.has(object.id)) {
-      let callback = this._callbacks.get(object.id);
+      const callback = this._callbacks.get(object.id);
       this._callbacks.delete(object.id);
       if (object.error)
         callback.reject(new Error(`Protocol error (${callback.method}): ${object.error.message} ${object.error.data}`));
@@ -211,7 +211,7 @@ class Session extends EventEmitter {
   }
 
   _onClosed() {
-    for (let callback of this._callbacks.values())
+    for (const callback of this._callbacks.values())
       callback.reject(new Error(`Protocol error (${callback.method}): Target closed.`));
     this._callbacks.clear();
     this._connection = null;

lib/ElementHandle.js

@@ -48,11 +48,11 @@ class ElementHandle {
     console.assert(!this._disposed, 'ElementHandle is disposed!');
     console.assert(typeof pageFunction === 'function', 'First argument to ElementHandle.evaluate must be a function!');
 
-    let stringifiedArgs = ['this'];
+    const stringifiedArgs = ['this'];
     stringifiedArgs.push(...args.map(x => JSON.stringify(x)));
-    let functionDeclaration = `function() { return (${pageFunction})(${stringifiedArgs.join(',')}) }`;
+    const functionDeclaration = `function() { return (${pageFunction})(${stringifiedArgs.join(',')}) }`;
     const objectId = this._remoteObject.objectId;
-    let { exceptionDetails, result: remoteObject } = await this._client.send('Runtime.callFunctionOn', { objectId, functionDeclaration, returnByValue: false, awaitPromise: true});
+    const { exceptionDetails, result: remoteObject } = await this._client.send('Runtime.callFunctionOn', { objectId, functionDeclaration, returnByValue: false, awaitPromise: true});
     if (exceptionDetails)
       throw new Error('Evaluation failed: ' + helper.getExceptionMessage(exceptionDetails));
     return await helper.serializeRemoteObject(this._client, remoteObject);
@@ -62,11 +62,11 @@ class ElementHandle {
    * @return {!Promise<{x: number, y: number}>}
    */
   async _visibleCenter() {
-    let center = await this.evaluate(element => {
+    const center = await this.evaluate(element => {
       if (!element.ownerDocument.contains(element))
         return null;
       element.scrollIntoViewIfNeeded();
-      let rect = element.getBoundingClientRect();
+      const rect = element.getBoundingClientRect();
       return {
         x: (Math.max(rect.left, 0) + Math.min(rect.right, window.innerWidth)) / 2,
         y: (Math.max(rect.top, 0) + Math.min(rect.bottom, window.innerHeight)) / 2
@@ -81,7 +81,7 @@ class ElementHandle {
    * @return {!Promise}
    */
   async hover() {
-    let {x, y} = await this._visibleCenter();
+    const {x, y} = await this._visibleCenter();
     await this._mouse.move(x, y);
   }
 
@@ -90,7 +90,7 @@ class ElementHandle {
    * @return {!Promise}
    */
   async click(options) {
-    let {x, y} = await this._visibleCenter();
+    const {x, y} = await this._visibleCenter();
     await this._mouse.click(x, y, options);
   }
 
@@ -99,7 +99,7 @@ class ElementHandle {
    * @return {!Promise}
    */
   async uploadFile(...filePaths) {
-    let files = filePaths.map(filePath => path.resolve(filePath));
+    const files = filePaths.map(filePath => path.resolve(filePath));
     const objectId = this._remoteObject.objectId;
     return this._client.send('DOM.setFileInputFiles', { objectId, files });
   }

lib/FrameManager.js

@@ -61,8 +61,8 @@ class FrameManager extends EventEmitter {
     if (this._frames.has(frameId))
       return;
     console.assert(parentFrameId);
-    let parentFrame = this._frames.get(parentFrameId);
+    const parentFrame = this._frames.get(parentFrameId);
-    let frame = new Frame(this._client, this._mouse, parentFrame, frameId);
+    const frame = new Frame(this._client, this._mouse, parentFrame, frameId);
     this._frames.set(frame._id, frame);
     this.emit(FrameManager.Events.FrameAttached, frame);
   }
@@ -77,7 +77,7 @@ class FrameManager extends EventEmitter {
 
     // Detach all child frames first.
     if (frame) {
-      for (let child of frame.childFrames())
+      for (const child of frame.childFrames())
         this._removeFramesRecursively(child);
     }
 
@@ -105,7 +105,7 @@ class FrameManager extends EventEmitter {
    * @param {string} frameId
    */
   _onFrameDetached(frameId) {
-    let frame = this._frames.get(frameId);
+    const frame = this._frames.get(frameId);
     if (frame)
       this._removeFramesRecursively(frame);
   }
@@ -116,7 +116,7 @@ class FrameManager extends EventEmitter {
     if (!frame)
       return;
     frame._defaultContextId = context.id;
-    for (let waitTask of frame._waitTasks)
+    for (const waitTask of frame._waitTasks)
       waitTask.rerun();
   }
 
@@ -124,7 +124,7 @@ class FrameManager extends EventEmitter {
    * @param {!Frame} frame
    */
   _removeFramesRecursively(frame) {
-    for (let child of frame.childFrames())
+    for (const child of frame.childFrames())
       this._removeFramesRecursively(child);
     frame._detach();
     this._frames.delete(frame._id);
@@ -179,7 +179,7 @@ class Frame {
    * @return {!Promise<(!Object|undefined)>}
    */
   async evaluate(pageFunction, ...args) {
-    let remoteObject = await this._rawEvaluate(pageFunction, ...args);
+    const remoteObject = await this._rawEvaluate(pageFunction, ...args);
     return await helper.serializeRemoteObject(this._client, remoteObject);
   }
 
@@ -188,7 +188,7 @@ class Frame {
    * @return {!Promise<?ElementHandle>}
    */
   async $(selector) {
-    let remoteObject = await this._rawEvaluate(selector => document.querySelector(selector), selector);
+    const remoteObject = await this._rawEvaluate(selector => document.querySelector(selector), selector);
     if (remoteObject.subtype === 'node')
       return new ElementHandle(this._client, remoteObject, this._mouse);
     helper.releaseObject(this._client, remoteObject);
@@ -201,9 +201,9 @@ class Frame {
    * @return {!Promise<(!Object|undefined)>}
    */
   async _rawEvaluate(pageFunction, ...args) {
-    let expression = helper.evaluationString(pageFunction, ...args);
+    const expression = helper.evaluationString(pageFunction, ...args);
     const contextId = this._defaultContextId;
-    let { exceptionDetails, result: remoteObject }  = await this._client.send('Runtime.evaluate', { expression, contextId, returnByValue: false, awaitPromise: true});
+    const { exceptionDetails, result: remoteObject }  = await this._client.send('Runtime.evaluate', { expression, contextId, returnByValue: false, awaitPromise: true});
     if (exceptionDetails)
       throw new Error('Evaluation failed: ' + helper.getExceptionMessage(exceptionDetails));
     return remoteObject;
@@ -270,9 +270,9 @@ class Frame {
      * @param {string} url
      */
     function addScriptTag(url) {
-      let script = document.createElement('script');
+      const script = document.createElement('script');
       script.src = url;
-      let promise = new Promise(x => script.onload = x);
+      const promise = new Promise(x => script.onload = x);
       document.head.appendChild(script);
       return promise;
     }
@@ -349,7 +349,7 @@ class Frame {
   }
 
   _detach() {
-    for (let waitTask of this._waitTasks)
+    for (const waitTask of this._waitTasks)
       waitTask.terminate(new Error('waitForSelector failed: frame got detached.'));
     this._detached = true;
     if (this._parentFrame)

lib/Input.js

@@ -166,7 +166,7 @@ class Mouse {
   }
 }
 
-let keys = {
+const keys = {
   'Cancel': 3,
   'Help': 6,
   'Backspace': 8,

lib/Launcher.js

@@ -113,7 +113,7 @@ class Launcher {
    * @return {!Promise<!Browser>}
    */
   static async connect({browserWSEndpoint, ignoreHTTPSErrors = false}) {
-    let connection = await Connection.create(browserWSEndpoint);
+    const connection = await Connection.create(browserWSEndpoint);
     return new Browser(connection, !!ignoreHTTPSErrors);
   }
 }
@@ -127,12 +127,12 @@ function waitForWSEndpoint(chromeProcess, timeout) {
   return new Promise((resolve, reject) => {
     const rl = readline.createInterface({ input: chromeProcess.stderr });
     let stderr = '';
-    let listeners = [
+    const listeners = [
       helper.addEventListener(rl, 'line', onLine),
       helper.addEventListener(rl, 'close', onClose),
       helper.addEventListener(chromeProcess, 'exit', onClose)
     ];
-    let timeoutId = timeout ? setTimeout(onTimeout, timeout) : 0;
+    const timeoutId = timeout ? setTimeout(onTimeout, timeout) : 0;
 
     function onClose() {
       cleanup();

lib/Multimap.js

@@ -61,7 +61,7 @@ class Multimap {
    * @return {boolean}
    */
   hasValue(key, value) {
-    let set = this._map.get(key);
+    const set = this._map.get(key);
     if (!set)
       return false;
     return set.has(value);
@@ -80,8 +80,8 @@ class Multimap {
    * @return {boolean}
    */
   delete(key, value) {
-    let values = this.get(key);
+    const values = this.get(key);
-    let result = values.delete(value);
+    const result = values.delete(value);
     if (!values.size)
       this._map.delete(key);
     return result;
@@ -99,7 +99,7 @@ class Multimap {
    * @return {?V} value
    */
   firstValue(key) {
-    let set = this._map.get(key);
+    const set = this._map.get(key);
     if (!set)
       return null;
     return set.values().next().value;
@@ -116,8 +116,8 @@ class Multimap {
    * @return {!Array<!V>}
    */
   valuesArray() {
-    let result = [];
+    const result = [];
-    for (let key of this._map.keys())
+    for (const key of this._map.keys())
       result.push(...Array.from(this._map.get(key).values()));
     return result;
   }

lib/NavigatorWatcher.js

@@ -40,19 +40,19 @@ class NavigatorWatcher {
 
     this._eventListeners = [];
 
-    let watchdog = new Promise(fulfill => this._maximumTimer = setTimeout(fulfill, this._timeout))
+    const watchdog = new Promise(fulfill => this._maximumTimer = setTimeout(fulfill, this._timeout))
         .then(() => 'Navigation Timeout Exceeded: ' + this._timeout + 'ms exceeded');
-    let navigationPromises = [watchdog];
+    const navigationPromises = [watchdog];
 
     if (!this._ignoreHTTPSErrors) {
-      let certificateError = new Promise(fulfill => {
+      const certificateError = new Promise(fulfill => {
         this._eventListeners.push(helper.addEventListener(this._client, 'Security.certificateError', fulfill));
       }).then(error => 'SSL Certificate error: ' + error.errorType);
       navigationPromises.push(certificateError);
     }
 
     if (this._waitUntil === 'load') {
-      let loadEventFired = new Promise(fulfill => {
+      const loadEventFired = new Promise(fulfill => {
         this._eventListeners.push(helper.addEventListener(this._client, 'Page.loadEventFired', fulfill));
       }).then(() => null);
       navigationPromises.push(loadEventFired);
@@ -64,7 +64,7 @@ class NavigatorWatcher {
         helper.addEventListener(this._client, 'Network.webSocketCreated', this._onLoadingStarted.bind(this)),
         helper.addEventListener(this._client, 'Network.webSocketClosed', this._onLoadingCompleted.bind(this)),
       ]);
-      let networkIdle = new Promise(fulfill => this._networkIdleCallback = fulfill).then(() => null);
+      const networkIdle = new Promise(fulfill => this._networkIdleCallback = fulfill).then(() => null);
       navigationPromises.push(networkIdle);
     }
 

lib/NetworkManager.js

@@ -51,8 +51,8 @@ class NetworkManager extends EventEmitter {
    */
   async setExtraHTTPHeaders(extraHTTPHeaders) {
     this._extraHTTPHeaders = new Map(extraHTTPHeaders);
-    let headers = {};
+    const headers = {};
-    for (let entry of extraHTTPHeaders.entries())
+    for (const entry of extraHTTPHeaders.entries())
       headers[entry[0]] = entry[1];
     await this._client.send('Network.setExtraHTTPHeaders', { headers });
   }
@@ -89,13 +89,13 @@ class NetworkManager extends EventEmitter {
     event.request.url = removeURLHash(event.request.url);
 
     if (event.redirectStatusCode) {
-      let request = this._interceptionIdToRequest.get(event.interceptionId);
+      const request = this._interceptionIdToRequest.get(event.interceptionId);
       console.assert(request, 'INTERNAL ERROR: failed to find request for interception redirect.');
       this._handleRequestRedirect(request, event.redirectStatusCode, event.redirectHeaders);
       this._handleRequestStart(request._requestId, event.interceptionId, event.redirectUrl, event.request);
       return;
     }
-    let requestHash = generateRequestHash(event.request);
+    const requestHash = generateRequestHash(event.request);
     this._requestHashToInterceptions.set(requestHash, event);
     this._maybeResolveInterception(requestHash);
   }
@@ -106,7 +106,7 @@ class NetworkManager extends EventEmitter {
    * @param {!Object} redirectHeaders
    */
   _handleRequestRedirect(request, redirectStatus, redirectHeaders) {
-    let response = new Response(this._client, request, redirectStatus, redirectHeaders);
+    const response = new Response(this._client, request, redirectStatus, redirectHeaders);
     request._response = response;
     this._requestIdToRequest.delete(request._requestId);
     this._interceptionIdToRequest.delete(request._interceptionId);
@@ -121,7 +121,7 @@ class NetworkManager extends EventEmitter {
    * @param {!Object} requestPayload
    */
   _handleRequestStart(requestId, interceptionId, url, requestPayload) {
-    let request = new Request(this._client, requestId, interceptionId, url, requestPayload);
+    const request = new Request(this._client, requestId, interceptionId, url, requestPayload);
     this._requestIdToRequest.set(requestId, request);
     this._interceptionIdToRequest.set(interceptionId, request);
     this.emit(NetworkManager.Events.Request, request);
@@ -135,13 +135,13 @@ class NetworkManager extends EventEmitter {
       // All redirects are handled in requestIntercepted.
       if (event.redirectResponse)
         return;
-      let requestHash = generateRequestHash(event.request);
+      const requestHash = generateRequestHash(event.request);
       this._requestHashToRequestIds.set(requestHash, event.requestId);
       this._maybeResolveInterception(requestHash);
       return;
     }
     if (event.redirectResponse) {
-      let request = this._requestIdToRequest.get(event.requestId);
+      const request = this._requestIdToRequest.get(event.requestId);
       this._handleRequestRedirect(request, event.redirectResponse.status, event.redirectResponse.headers);
     }
     this._handleRequestStart(event.requestId, null, event.request.url, event.request);
@@ -165,11 +165,11 @@ class NetworkManager extends EventEmitter {
    * @param {!Object} event
    */
   _onResponseReceived(event) {
-    let request = this._requestIdToRequest.get(event.requestId);
+    const request = this._requestIdToRequest.get(event.requestId);
     // FileUpload sends a response without a matching request.
     if (!request)
       return;
-    let response = new Response(this._client, request, event.response.status, event.response.headers);
+    const response = new Response(this._client, request, event.response.status, event.response.headers);
     request._response = response;
     this.emit(NetworkManager.Events.Response, response);
   }
@@ -178,7 +178,7 @@ class NetworkManager extends EventEmitter {
    * @param {!Object} event
    */
   _onLoadingFinished(event) {
-    let request = this._requestIdToRequest.get(event.requestId);
+    const request = this._requestIdToRequest.get(event.requestId);
     // For certain requestIds we never receive requestWillBeSent event.
     // @see https://crbug.com/750469
     if (!request)
@@ -193,7 +193,7 @@ class NetworkManager extends EventEmitter {
    * @param {!Object} event
    */
   _onLoadingFailed(event) {
-    let request = this._requestIdToRequest.get(event.requestId);
+    const request = this._requestIdToRequest.get(event.requestId);
     // For certain requestIds we never receive requestWillBeSent event.
     // @see https://crbug.com/750469
     if (!request)
@@ -249,7 +249,7 @@ class Request {
     let headers = undefined;
     if (overrides.headers) {
       headers = {};
-      for (let entry of overrides.headers)
+      for (const entry of overrides.headers)
         headers[entry[0]] = entry[1];
     }
     this._client.send('Network.continueInterceptedRequest', {
@@ -300,7 +300,7 @@ class Response {
   buffer() {
     if (!this._contentPromise) {
       this._contentPromise = this._request._completePromise.then(async() => {
-        let response = await this._client.send('Network.getResponseBody', {
+        const response = await this._client.send('Network.getResponseBody', {
           requestId: this._request._requestId
         });
         return Buffer.from(response.body, response.base64Encoded ? 'base64' : 'utf8');
@@ -313,7 +313,7 @@ class Response {
    * @return {!Promise<string>}
    */
   async text() {
-    let content = await this.buffer();
+    const content = await this.buffer();
     return content.toString('utf8');
   }
 
@@ -321,7 +321,7 @@ class Response {
    * @return {!Promise<!Object>}
    */
   async json() {
-    let content = await this.text();
+    const content = await this.text();
     return JSON.parse(content);
   }
 
@@ -339,15 +339,15 @@ helper.tracePublicAPI(Response);
  * @return {string}
  */
 function generateRequestHash(request) {
-  let hash = {
+  const hash = {
     url: request.url,
     method: request.method,
     postData: request.postData,
     headers: {},
   };
-  let headers = Object.keys(request.headers);
+  const headers = Object.keys(request.headers);
   headers.sort();
-  for (let header of headers) {
+  for (const header of headers) {
     if (header === 'Accept' || header === 'Referer' || header === 'X-DevTools-Emulate-Network-Conditions-Client-Id')
       continue;
     hash.headers[header] = request.headers[header];
@@ -360,7 +360,7 @@ function generateRequestHash(request) {
  * @return {string}
  */
 function removeURLHash(url) {
-  let urlObject = new URL(url);
+  const urlObject = new URL(url);
   urlObject.hash = '';
   return urlObject.toString();
 }

lib/Page.js

@@ -171,7 +171,7 @@ class Page extends EventEmitter {
       throw new Error(`Failed to add page binding with name ${name}: window['${name}'] already exists!`);
     this._pageBindings[name] = puppeteerFunction;
 
-    let expression = helper.evaluationString(addPageBinding, name);
+    const expression = helper.evaluationString(addPageBinding, name);
     await this._client.send('Page.addScriptToEvaluateOnNewDocument', { source: expression });
     await this._client.send('Runtime.evaluate', { expression, returnByValue: true });
 
@@ -213,15 +213,15 @@ class Page extends EventEmitter {
    * @param {!Object} exceptionDetails
    */
   _handleException(exceptionDetails) {
-    let message = helper.getExceptionMessage(exceptionDetails);
+    const message = helper.getExceptionMessage(exceptionDetails);
     this.emit(Page.Events.PageError, new Error(message));
   }
 
   async _onConsoleAPI(event) {
     if (event.type === 'debug' && event.args.length && event.args[0].value === 'driver:page-binding') {
-      let {name, seq, args} = JSON.parse(event.args[1].value);
+      const {name, seq, args} = JSON.parse(event.args[1].value);
-      let result = await this._pageBindings[name](...args);
+      const result = await this._pageBindings[name](...args);
-      let expression = helper.evaluationString(deliverResult, name, seq, result);
+      const expression = helper.evaluationString(deliverResult, name, seq, result);
       this._client.send('Runtime.evaluate', { expression });
 
       function deliverResult(name, seq, result) {
@@ -234,7 +234,7 @@ class Page extends EventEmitter {
       event.args.map(arg => helper.releaseObject(this._client, arg));
       return;
     }
-    let values = await Promise.all(event.args.map(arg => helper.serializeRemoteObject(this._client, arg)));
+    const values = await Promise.all(event.args.map(arg => helper.serializeRemoteObject(this._client, arg)));
     this.emit(Page.Events.Console, ...values);
   }
 
@@ -249,7 +249,7 @@ class Page extends EventEmitter {
     else if (event.type === 'beforeunload')
       dialogType = Dialog.Type.BeforeUnload;
     console.assert(dialogType, 'Unknown javascript dialog type: ' + event.type);
-    let dialog = new Dialog(this._client, dialogType, event.message, event.defaultPrompt);
+    const dialog = new Dialog(this._client, dialogType, event.message, event.defaultPrompt);
     this.emit(Page.Events.Dialog, dialog);
   }
 
@@ -419,7 +419,7 @@ class Page extends EventEmitter {
    * @return {!Promise}
    */
   async evaluateOnNewDocument(pageFunction, ...args) {
-    let source = helper.evaluationString(pageFunction, ...args);
+    const source = helper.evaluationString(pageFunction, ...args);
     await this._client.send('Page.addScriptToEvaluateOnNewDocument', { source });
   }
 
@@ -430,7 +430,7 @@ class Page extends EventEmitter {
   async screenshot(options = {}) {
     let screenshotType = null;
     if (options.path) {
-      let mimeType = mime.lookup(options.path);
+      const mimeType = mime.lookup(options.path);
       if (mimeType === 'image/png')
         screenshotType = 'png';
       else if (mimeType === 'image/jpeg')
@@ -488,14 +488,14 @@ class Page extends EventEmitter {
 
     if (options.omitBackground)
       await this._client.send('Emulation.setDefaultBackgroundColorOverride', { color: { r: 0, g: 0, b: 0, a: 0 } });
-    let result = await this._client.send('Page.captureScreenshot', { format, quality: options.quality, clip });
+    const result = await this._client.send('Page.captureScreenshot', { format, quality: options.quality, clip });
     if (options.omitBackground)
       await this._client.send('Emulation.setDefaultBackgroundColorOverride');
 
     if (options.fullPage)
       await this.setViewport(this._viewport);
 
-    let buffer = new Buffer(result.data, 'base64');
+    const buffer = new Buffer(result.data, 'base64');
     if (options.path)
       fs.writeFileSync(options.path, buffer);
     return buffer;
@@ -506,16 +506,16 @@ class Page extends EventEmitter {
    * @return {!Promise<!Buffer>}
    */
   async pdf(options = {}) {
-    let scale = options.scale || 1;
+    const scale = options.scale || 1;
-    let displayHeaderFooter = !!options.displayHeaderFooter;
+    const displayHeaderFooter = !!options.displayHeaderFooter;
-    let printBackground = !!options.printBackground;
+    const printBackground = !!options.printBackground;
-    let landscape = !!options.landscape;
+    const landscape = !!options.landscape;
-    let pageRanges = options.pageRanges || '';
+    const pageRanges = options.pageRanges || '';
 
     let paperWidth = 8.5;
     let paperHeight = 11;
     if (options.format) {
-      let format = Page.PaperFormats[options.format.toLowerCase()];
+      const format = Page.PaperFormats[options.format.toLowerCase()];
       console.assert(format, 'Unknown paper format: ' + options.format);
       paperWidth = format.width;
       paperHeight = format.height;
@@ -524,13 +524,13 @@ class Page extends EventEmitter {
       paperHeight = convertPrintParameterToInches(options.height) || paperHeight;
     }
 
-    let marginOptions = options.margin || {};
+    const marginOptions = options.margin || {};
-    let marginTop = convertPrintParameterToInches(marginOptions.top) || 0;
+    const marginTop = convertPrintParameterToInches(marginOptions.top) || 0;
-    let marginLeft = convertPrintParameterToInches(marginOptions.left) || 0;
+    const marginLeft = convertPrintParameterToInches(marginOptions.left) || 0;
-    let marginBottom = convertPrintParameterToInches(marginOptions.bottom) || 0;
+    const marginBottom = convertPrintParameterToInches(marginOptions.bottom) || 0;
-    let marginRight = convertPrintParameterToInches(marginOptions.right) || 0;
+    const marginRight = convertPrintParameterToInches(marginOptions.right) || 0;
 
-    let result = await this._client.send('Page.printToPDF', {
+    const result = await this._client.send('Page.printToPDF', {
       landscape: landscape,
       displayHeaderFooter: displayHeaderFooter,
       printBackground: printBackground,
@@ -543,7 +543,7 @@ class Page extends EventEmitter {
       marginRight: marginRight,
       pageRanges: pageRanges
     });
-    let buffer = new Buffer(result.data, 'base64');
+    const buffer = new Buffer(result.data, 'base64');
     if (options.path)
       fs.writeFileSync(options.path, buffer);
     return buffer;
@@ -583,7 +583,7 @@ class Page extends EventEmitter {
    * @return {!Promise}
    */
   async click(selector, options) {
-    let handle = await this.$(selector);
+    const handle = await this.$(selector);
     console.assert(handle, 'No node found for selector: ' + selector);
     await handle.click(options);
     await handle.dispose();
@@ -594,7 +594,7 @@ class Page extends EventEmitter {
    * @param {!Promise}
    */
   async hover(selector) {
-    let handle = await this.$(selector);
+    const handle = await this.$(selector);
     console.assert(handle, 'No node found for selector: ' + selector);
     await handle.hover();
     await handle.dispose();
@@ -605,7 +605,7 @@ class Page extends EventEmitter {
    * @return {!Promise}
    */
   async focus(selector) {
-    let handle = await this.$(selector);
+    const handle = await this.$(selector);
     console.assert(handle, 'No node found for selector: ' + selector);
     await handle.evaluate(element => element.focus());
     await handle.dispose();
@@ -621,7 +621,7 @@ class Page extends EventEmitter {
     if (options && options.delay)
       delay = options.delay;
     let last;
-    for (let char of text) {
+    for (const char of text) {
       last = this.press(char, {text: char, delay});
       if (delay)
         await new Promise(f => setTimeout(f, delay));
@@ -684,7 +684,7 @@ Page.PaperFormats = {
   a5: {width: 5.83, height: 8.27 },
 };
 
-let unitToPixels = {
+const unitToPixels = {
   'px': 1,
   'in': 96,
   'cm': 37.8,
@@ -703,7 +703,7 @@ function convertPrintParameterToInches(parameter) {
     // Treat numbers as pixel values to be aligned with phantom's paperSize.
     pixels = /** @type {number} */ (parameter);
   } else if (helper.isString(parameter)) {
-    let text = parameter;
+    const text = parameter;
     let unit = text.substring(text.length - 2).toLowerCase();
     let valueText = '';
     if (unitToPixels.hasOwnProperty(unit)) {
@@ -714,7 +714,7 @@ function convertPrintParameterToInches(parameter) {
       unit = 'px';
       valueText = text;
     }
-    let value = Number(valueText);
+    const value = Number(valueText);
     console.assert(!isNaN(value), 'Failed to parse parameter value: ' + text);
     pixels = value * unitToPixels[unit];
   } else {

lib/Tracing.js

@@ -57,7 +57,7 @@ class Tracing {
    */
   async stop() {
     let fulfill;
-    let contentPromise = new Promise(x => fulfill = x);
+    const contentPromise = new Promise(x => fulfill = x);
     this._client.once('Tracing.tracingComplete', event => {
       this._readStream(event.stream, this._path).then(fulfill);
     });
@@ -73,9 +73,9 @@ class Tracing {
    */
   async _readStream(handle, path) {
     let eof = false;
-    let file = fs.openSync(path, 'w');
+    const file = fs.openSync(path, 'w');
     while (!eof) {
-      let response = await this._client.send('IO.read', {handle});
+      const response = await this._client.send('IO.read', {handle});
       eof = response.eof;
       if (path)
         fs.writeSync(file, response.data);

lib/helper.js

@@ -39,9 +39,9 @@ class Helper {
       return exceptionDetails.exception.description;
     let message = exceptionDetails.text;
     if (exceptionDetails.stackTrace) {
-      for (let callframe of exceptionDetails.stackTrace.callFrames) {
+      for (const callframe of exceptionDetails.stackTrace.callFrames) {
-        let location = callframe.url + ':' + callframe.lineNumber + ':' + callframe.columnNumber;
+        const location = callframe.url + ':' + callframe.lineNumber + ':' + callframe.columnNumber;
-        let functionName = callframe.functionName || '<anonymous>';
+        const functionName = callframe.functionName || '<anonymous>';
         message += `\n    at ${functionName} (${location})`;
       }
     }
@@ -73,7 +73,7 @@ class Helper {
     if (remoteObject.subtype === 'promise')
       return remoteObject.description;
     try {
-      let response = await client.send('Runtime.callFunctionOn', {
+      const response = await client.send('Runtime.callFunctionOn', {
         objectId: remoteObject.objectId,
         functionDeclaration: 'function() { return this; }',
         returnByValue: true,
@@ -112,15 +112,15 @@ class Helper {
     const debug = require('debug')(`puppeteer:${className}`);
     if (!debug.enabled && !apiCoverage)
       return;
-    for (let methodName of Reflect.ownKeys(classType.prototype)) {
+    for (const methodName of Reflect.ownKeys(classType.prototype)) {
       const method = Reflect.get(classType.prototype, methodName);
       if (methodName === 'constructor' || typeof methodName !== 'string' || methodName.startsWith('_') || typeof method !== 'function')
         continue;
       if (apiCoverage)
         apiCoverage.set(`${className}.${methodName}`, false);
       Reflect.set(classType.prototype, methodName, function(...args) {
-        let argsText = args.map(stringifyArgument).join(', ');
+        const argsText = args.map(stringifyArgument).join(', ');
-        let callsite = `${className}.${methodName}(${argsText})`;
+        const callsite = `${className}.${methodName}(${argsText})`;
         if (debug.enabled)
           debug(callsite);
         if (apiCoverage)
@@ -131,12 +131,12 @@ class Helper {
 
     if (classType.Events) {
       if (apiCoverage) {
-        for (let event of Object.values(classType.Events))
+        for (const event of Object.values(classType.Events))
           apiCoverage.set(`${className}.emit(${JSON.stringify(event)})`, false);
       }
       const method = Reflect.get(classType.prototype, 'emit');
       Reflect.set(classType.prototype, 'emit', function(event, ...args) {
-        let argsText = [JSON.stringify(event)].concat(args.map(stringifyArgument)).join(', ');
+        const argsText = [JSON.stringify(event)].concat(args.map(stringifyArgument)).join(', ');
         if (debug.enabled && this.listenerCount(event))
           debug(`${className}.emit(${argsText})`);
         if (apiCoverage && this.listenerCount(event))
@@ -160,7 +160,7 @@ class Helper {
       }
       const state = {};
       const keys = Object.keys(arg);
-      for (let key of keys) {
+      for (const key of keys) {
         const value = arg[key];
         if (Helper.isString(value) || Helper.isNumber(value))
           state[key] = JSON.stringify(value);
@@ -185,7 +185,7 @@ class Helper {
    * @param {!Array<{emitter: !EventEmitter, eventName: string, handler: function(?)}>}
    */
   static removeEventListeners(listeners) {
-    for (let listener of listeners)
+    for (const listener of listeners)
       listener.emitter.removeListener(listener.eventName, listener.handler);
     listeners.splice(0, listeners.length);
   }

phantom_shim/FileSystem.js

@@ -68,7 +68,7 @@ class FileSystem {
      * @param {string} toPath
      */
   copy(fromPath, toPath) {
-    let content = fs.readFileSync(fromPath);
+    const content = fs.readFileSync(fromPath);
     fs.writeFileSync(toPath, content);
   }
 
@@ -77,7 +77,7 @@ class FileSystem {
      * @param {string} toPath
      */
   move(fromPath, toPath) {
-    let content = fs.readFileSync(fromPath);
+    const content = fs.readFileSync(fromPath);
     fs.writeFileSync(toPath, content);
     fs.unlinkSync(fromPath);
   }
@@ -170,7 +170,7 @@ class FileSystem {
      * @param {string} mode
      */
   write(filePath, data, mode) {
-    let fd = new FileDescriptor(filePath, mode, 'utf8');
+    const fd = new FileDescriptor(filePath, mode, 'utf8');
     fd.write(data);
     fd.close();
   }
@@ -288,8 +288,8 @@ class FileSystem {
   }
 }
 
-let fdwrite = deasync(fs.write);
+const fdwrite = deasync(fs.write);
-let fdread = deasync(fs.read);
+const fdread = deasync(fs.read);
 
 class FileDescriptor {
   /**
@@ -318,8 +318,8 @@ class FileDescriptor {
      * @param {string} data
      */
   write(data) {
-    let buffer = Buffer.from(data, this._encoding);
+    const buffer = Buffer.from(data, this._encoding);
-    let written = fdwrite(this._fd, buffer, 0, buffer.length, this._position);
+    const written = fdwrite(this._fd, buffer, 0, buffer.length, this._position);
     this._position += written;
   }
 
@@ -344,8 +344,8 @@ class FileDescriptor {
       size = fs.fstatSync(this._fd).size;
       position = 0;
     }
-    let buffer = new Buffer(size);
+    const buffer = new Buffer(size);
-    let bytesRead = fdread(this._fd, buffer, 0, size, position);
+    const bytesRead = fdread(this._fd, buffer, 0, size, position);
     this._position += bytesRead;
     return buffer.toString(this._encoding);
   }

phantom_shim/Phantom.js

@@ -123,7 +123,7 @@ module.exports.create = function(context, scriptPath) {
      * @param {string} filename
      */
     loadModule: function(moduleSource, filename) {
-      let code = [
+      const code = [
         '(function(require, exports, module) {\n',
         moduleSource,
         '\n}.call({},',

phantom_shim/System.js

@@ -61,7 +61,7 @@ class StandardInput {
     if (this._closed && !this._lines.length)
       return '';
     if (!this._lines.length) {
-      let linePromise = new Promise(fulfill => this._readline.once('line', fulfill));
+      const linePromise = new Promise(fulfill => this._readline.once('line', fulfill));
       await(linePromise);
     }
     return this._lines.shift();
@@ -72,10 +72,10 @@ class StandardInput {
      */
   read() {
     if (!this._closed) {
-      let closePromise = new Promise(fulfill => this._readline.once('close', fulfill));
+      const closePromise = new Promise(fulfill => this._readline.once('close', fulfill));
       await(closePromise);
     }
-    let text = this._lines.join('\n');
+    const text = this._lines.join('\n');
     this._lines = [];
     return text;
   }

phantom_shim/WebPage.js

@@ -152,7 +152,7 @@ class WebPage {
    * @return {string}
    */
   get focusedFrameName() {
-    let focusedFrame = this._focusedFrame();
+    const focusedFrame = this._focusedFrame();
     return focusedFrame ? focusedFrame.name() : '';
   }
 
@@ -160,10 +160,10 @@ class WebPage {
    * @return {?Frame}
    */
   _focusedFrame() {
-    let frames = this._currentFrame.childFrames().slice();
+    const frames = this._currentFrame.childFrames().slice();
     frames.push(this._currentFrame);
-    let promises = frames.map(frame => frame.evaluate(() => document.hasFocus()));
+    const promises = frames.map(frame => frame.evaluate(() => document.hasFocus()));
-    let result = await(Promise.all(promises));
+    const result = await(Promise.all(promises));
     for (let i = 0; i < result.length; ++i) {
       if (result[i])
         return frames[i];
@@ -172,7 +172,7 @@ class WebPage {
   }
 
   switchToFocusedFrame() {
-    let frame = this._focusedFrame();
+    const frame = this._focusedFrame();
     this._currentFrame = frame;
   }
 
@@ -196,7 +196,7 @@ class WebPage {
    * @return {boolean}
    */
   switchToParentFrame() {
-    let frame = this._currentFrame.parentFrame();
+    const frame = this._currentFrame.parentFrame();
     if (!frame)
       return false;
     this._currentFrame = frame;
@@ -236,8 +236,8 @@ class WebPage {
   _onRequest(request) {
     if (!this._onResourceRequestedCallback)
       return;
-    let requestData = new RequestData(request);
+    const requestData = new RequestData(request);
-    let phantomRequest = new PhantomRequest();
+    const phantomRequest = new PhantomRequest();
     this._onResourceRequestedCallback.call(null, requestData, phantomRequest);
     if (phantomRequest._aborted) {
       request.abort();
@@ -252,14 +252,14 @@ class WebPage {
   _onResponseReceived(response) {
     if (!this.onResourceReceived)
       return;
-    let phantomResponse = new PhantomResponse(response, false /* isResponseFinished */);
+    const phantomResponse = new PhantomResponse(response, false /* isResponseFinished */);
     this.onResourceReceived.call(null, phantomResponse);
   }
 
   _onRequestFinished(request) {
     if (!this.onResourceReceived)
       return;
-    let phantomResponse = new PhantomResponse(request.response(), true /* isResponseFinished */);
+    const phantomResponse = new PhantomResponse(request.response(), true /* isResponseFinished */);
     this.onResourceReceived.call(null, phantomResponse);
   }
 
@@ -391,10 +391,10 @@ class WebPage {
       this._onAlertCallback.call(null, dialog.message());
       await(dialog.accept());
     } else if (dialog.type === 'confirm' && this._onConfirmCallback) {
-      let result = this._onConfirmCallback.call(null, dialog.message());
+      const result = this._onConfirmCallback.call(null, dialog.message());
       await(result ? dialog.accept() : dialog.dismiss());
     } else if (dialog.type === 'prompt' && this._onPromptCallback) {
-      let result = this._onPromptCallback.call(null, dialog.message(), dialog.defaultValue());
+      const result = this._onPromptCallback.call(null, dialog.message(), dialog.defaultValue());
       await(result ? dialog.accept(result) : dialog.dismiss());
     }
   }
@@ -449,7 +449,7 @@ class WebPage {
           await(this._page.keyboard.up(String.fromCharCode(keyOrKeys)));
           break;
         }
-        for (let key of keyOrKeys)
+        for (const key of keyOrKeys)
           await(this._page.keyboard.up(key));
         break;
       case 'keypress':
@@ -475,7 +475,7 @@ class WebPage {
           await(this._page.keyboard.down(String.fromCharCode(keyOrKeys)));
           break;
         }
-        for (let key of keyOrKeys)
+        for (const key of keyOrKeys)
           await(this._page.keyboard.down(key));
         break;
     }
@@ -539,7 +539,7 @@ class WebPage {
           errorString: 'SSL handshake failed'
         });
       }
-      let status = error ? 'fail' : 'success';
+      const status = error ? 'fail' : 'success';
       if (this.onLoadFinished)
         this.onLoadFinished.call(null, status);
       if (callback)
@@ -574,8 +574,8 @@ class WebPage {
    */
   render(fileName) {
     if (fileName.endsWith('pdf')) {
-      let options = {};
+      const options = {};
-      let paperSize = this.paperSize || {};
+      const paperSize = this.paperSize || {};
       options.margin = paperSize.margin;
       options.format = paperSize.format;
       options.landscape = paperSize.orientation === 'landscape';
@@ -584,7 +584,7 @@ class WebPage {
       options.path = fileName;
       await(this._page.pdf(options));
     } else {
-      let options = {};
+      const options = {};
       if (this.clipRect && (this.clipRect.left || this.clipRect.top || this.clipRect.width || this.clipRect.height)) {
         options.clip = {
           x: this.clipRect.left,
@@ -669,7 +669,7 @@ class PhantomResponse {
     this.statusText = response.statusText;
     this.stage = isResponseFinished ? 'end' : 'start';
     this.headers = [];
-    for (let entry of response.headers.entries()) {
+    for (const entry of response.headers.entries()) {
       this.headers.push({
         name: entry[0],
         value: entry[1]
@@ -685,7 +685,7 @@ class RequestData {
   constructor(request) {
     this.url = request.url,
     this.headers = {};
-    for (let entry of request.headers.entries())
+    for (const entry of request.headers.entries())
       this.headers[entry[0]] = entry[1];
   }
 }
@@ -714,7 +714,7 @@ class AsyncEmitter extends EventEmitter {
 
   _onListenerAdded(event, listener) {
     // Async listener calls original listener on next tick.
-    let asyncListener = (...args) => {
+    const asyncListener = (...args) => {
       process.nextTick(() => listener.apply(null, args));
     };
     listener[this._symbol] = asyncListener;

phantom_shim/WebServer.js

@@ -47,17 +47,17 @@ class WebServer {
       return false;
     this.newRequest = callback;
     this._server.listen(port);
-    let errorPromise = new Promise(x => this._server.once('error', x));
+    const errorPromise = new Promise(x => this._server.once('error', x));
-    let successPromise = new Promise(x => this._server.once('listening', x));
+    const successPromise = new Promise(x => this._server.once('listening', x));
     await(Promise.race([errorPromise, successPromise]));
     if (!this._server.listening)
       return false;
 
     this._server.on('request', (req, res) => {
       res.close = res.end.bind(res);
-      let headers = res.getHeaders();
+      const headers = res.getHeaders();
       res.headers = [];
-      for (let key in headers) {
+      for (const key in headers) {
         res.headers.push({
           name: key,
           value: headers[key]
@@ -65,7 +65,7 @@ class WebServer {
       }
       res.header = res.getHeader;
       res.setHeaders = headers => {
-        for (let key in headers)
+        for (const key in headers)
           res.setHeader(key, headers[key]);
       };
       Object.defineProperty(res, 'statusCode', {

phantom_shim/runner.js

@@ -43,21 +43,21 @@ if (argv['ssl-certificates-path']) {
   return;
 }
 
-let scriptArguments = argv._;
+const scriptArguments = argv._;
 if (!scriptArguments.length) {
   console.log(__filename.split('/').pop() + ' [scriptfile]');
   return;
 }
 
-let scriptPath = path.resolve(process.cwd(), scriptArguments[0]);
+const scriptPath = path.resolve(process.cwd(), scriptArguments[0]);
 if (!fs.existsSync(scriptPath)) {
   console.error(`script not found: ${scriptPath}`);
   process.exit(1);
   return;
 }
 
-let context = createPhantomContext(argv.headless, scriptPath, argv);
+const context = createPhantomContext(argv.headless, scriptPath, argv);
-let scriptContent = fs.readFileSync(scriptPath, 'utf8');
+const scriptContent = fs.readFileSync(scriptPath, 'utf8');
 vm.runInContext(scriptContent, context);
 
 /**
@@ -67,7 +67,7 @@ vm.runInContext(scriptContent, context);
  * @return {!Object}
  */
 function createPhantomContext(headless, scriptPath, argv) {
-  let context = {};
+  const context = {};
   let browser = null;
   context.setInterval = setInterval;
   context.setTimeout = setTimeout;
@@ -81,7 +81,7 @@ function createPhantomContext(headless, scriptPath, argv) {
 
   vm.createContext(context);
 
-  let nativeExports = {
+  const nativeExports = {
     fs: new FileSystem(),
     system: new System(argv._),
     webpage: {
@@ -95,8 +95,8 @@ function createPhantomContext(headless, scriptPath, argv) {
     },
     child_process: child_process
   };
-  let bootstrapPath = path.join(__dirname, '..', 'third_party', 'phantomjs', 'bootstrap.js');
+  const bootstrapPath = path.join(__dirname, '..', 'third_party', 'phantomjs', 'bootstrap.js');
-  let bootstrapCode = fs.readFileSync(bootstrapPath, 'utf8');
+  const bootstrapCode = fs.readFileSync(bootstrapPath, 'utf8');
   vm.runInContext(bootstrapCode, context, {
     filename: 'bootstrap.js'
   })(nativeExports);

test/assets/input/mouse-helper.js

@@ -1,9 +1,9 @@
 // This injects a box into the page that moves with the mouse;
 // Useful for debugging
 (function(){
-  let box = document.createElement('div');
+  const box = document.createElement('div');
   box.classList.add('mouse-helper');
-  let styleElement = document.createElement('style');
+  const styleElement = document.createElement('style');
   styleElement.innerHTML = `
   .mouse-helper {
     pointer-events: none;

test/frame-utils.js

@@ -25,7 +25,7 @@ const utils = module.exports = {
     await page.evaluate(attachFrame, frameId, url);
 
     function attachFrame(frameId, url) {
-      let frame = document.createElement('iframe');
+      const frame = document.createElement('iframe');
       frame.src = url;
       frame.id = frameId;
       document.body.appendChild(frame);
@@ -42,7 +42,7 @@ const utils = module.exports = {
     await page.evaluate(detachFrame, frameId);
 
     function detachFrame(frameId) {
-      let frame = document.getElementById(frameId);
+      const frame = document.getElementById(frameId);
       frame.remove();
     }
   },
@@ -57,7 +57,7 @@ const utils = module.exports = {
     await page.evaluate(navigateFrame, frameId, url);
 
     function navigateFrame(frameId, url) {
-      let frame = document.getElementById(frameId);
+      const frame = document.getElementById(frameId);
       frame.src = url;
       return new Promise(x => frame.onload = x);
     }
@@ -71,7 +71,7 @@ const utils = module.exports = {
   dumpFrames: function(frame, indentation) {
     indentation = indentation || '';
     let result = indentation + frame.url();
-    for (let child of frame.childFrames())
+    for (const child of frame.childFrames())
       result += '\n' + utils.dumpFrames(child, '    ' + indentation);
     return result;
   },

test/golden-utils.js

@@ -30,7 +30,7 @@ module.exports = {
   },
 };
 
-let GoldenComparators = {
+const GoldenComparators = {
   'image/png': compareImages,
   'text/plain': compareText
 };
@@ -44,15 +44,15 @@ function compareImages(actualBuffer, expectedBuffer) {
   if (!actualBuffer || !(actualBuffer instanceof Buffer))
     return { errorMessage: 'Actual result should be Buffer.' };
 
-  let actual = PNG.sync.read(actualBuffer);
+  const actual = PNG.sync.read(actualBuffer);
-  let expected = PNG.sync.read(expectedBuffer);
+  const expected = PNG.sync.read(expectedBuffer);
   if (expected.width !== actual.width || expected.height !== actual.height) {
     return {
       errorMessage: `Sizes differ: expected image ${expected.width}px X ${expected.height}px, but got ${actual.width}px X ${actual.height}px. `
     };
   }
-  let diff = new PNG({width: expected.width, height: expected.height});
+  const diff = new PNG({width: expected.width, height: expected.height});
-  let count = pixelmatch(expected.data, actual.data, diff.data, expected.width, expected.height, {threshold: 0.1});
+  const count = pixelmatch(expected.data, actual.data, diff.data, expected.width, expected.height, {threshold: 0.1});
   return count > 0 ? { diff: PNG.sync.write(diff) } : null;
 }
 
@@ -64,14 +64,14 @@ function compareImages(actualBuffer, expectedBuffer) {
 function compareText(actual, expectedBuffer) {
   if (typeof actual !== 'string')
     return { errorMessage: 'Actual result should be string' };
-  let expected = expectedBuffer.toString('utf-8');
+  const expected = expectedBuffer.toString('utf-8');
   if (expected === actual)
     return null;
-  let diff = new Diff();
+  const diff = new Diff();
-  let result = diff.main(expected, actual);
+  const result = diff.main(expected, actual);
   diff.cleanupSemantic(result);
   let html = diff.prettyHtml(result);
-  let diffStylePath = path.join(__dirname, 'diffstyle.css');
+  const diffStylePath = path.join(__dirname, 'diffstyle.css');
   html = `<link rel="stylesheet" href="file://${diffStylePath}">` + html;
   return {
     diff: html,
@@ -85,10 +85,10 @@ function compareText(actual, expectedBuffer) {
  * @return {!{pass: boolean, message: (undefined|string)}}
  */
 function compare(goldenPath, outputPath, actual, goldenName) {
-  let expectedPath = path.join(goldenPath, goldenName);
+  const expectedPath = path.join(goldenPath, goldenName);
-  let actualPath = path.join(outputPath, goldenName);
+  const actualPath = path.join(outputPath, goldenName);
 
-  let messageSuffix = 'Output is saved in "' + path.basename(outputPath + '" directory');
+  const messageSuffix = 'Output is saved in "' + path.basename(outputPath + '" directory');
 
   if (!fs.existsSync(expectedPath)) {
     ensureOutputDir();
@@ -98,15 +98,15 @@ function compare(goldenPath, outputPath, actual, goldenName) {
       message: goldenName + ' is missing in golden results. ' + messageSuffix
     };
   }
-  let expected = fs.readFileSync(expectedPath);
+  const expected = fs.readFileSync(expectedPath);
-  let comparator = GoldenComparators[mime.lookup(goldenName)];
+  const comparator = GoldenComparators[mime.lookup(goldenName)];
   if (!comparator) {
     return {
       pass: false,
       message: 'Failed to find comparator with type ' + mime.lookup(goldenName) + ': '  + goldenName
     };
   }
-  let result = comparator(actual, expected);
+  const result = comparator(actual, expected);
   if (!result)
     return { pass: true };
   ensureOutputDir();
@@ -114,7 +114,7 @@ function compare(goldenPath, outputPath, actual, goldenName) {
   // Copy expected to the output/ folder for convenience.
   fs.writeFileSync(addSuffix(actualPath, '-expected'), expected);
   if (result.diff) {
-    let diffPath = addSuffix(actualPath, '-diff', result.diffExtension);
+    const diffPath = addSuffix(actualPath, '-diff', result.diffExtension);
     fs.writeFileSync(diffPath, result.diff);
   }
 
@@ -139,8 +139,8 @@ function compare(goldenPath, outputPath, actual, goldenName) {
  * @return {string}
  */
 function addSuffix(filePath, suffix, customExtension) {
-  let dirname = path.dirname(filePath);
+  const dirname = path.dirname(filePath);
-  let ext = path.extname(filePath);
+  const ext = path.extname(filePath);
-  let name = path.basename(filePath, ext);
+  const name = path.basename(filePath, ext);
   return path.join(dirname, name + suffix + (customExtension || ext));
 }

test/server/SimpleServer.js

@@ -32,7 +32,7 @@ class SimpleServer {
    * @return {!SimpleServer}
    */
   static async create(dirPath, port) {
-    let server = new SimpleServer(dirPath, port);
+    const server = new SimpleServer(dirPath, port);
     await new Promise(x => server._server.once('listening', x));
     return server;
   }
@@ -43,7 +43,7 @@ class SimpleServer {
    * @return {!SimpleServer}
    */
   static async createHTTPS(dirPath, port) {
-    let server = new SimpleServer(dirPath, port, {
+    const server = new SimpleServer(dirPath, port, {
       key: fs.readFileSync(path.join(__dirname, 'key.pem')),
       cert: fs.readFileSync(path.join(__dirname, 'cert.pem')),
       passphrase: 'aaaa',
@@ -93,7 +93,7 @@ class SimpleServer {
    */
   async stop() {
     this.reset();
-    for (let socket of this._sockets)
+    for (const socket of this._sockets)
       socket.destroy();
     this._sockets.clear();
     await new Promise(x => this._server.close(x));
@@ -139,8 +139,8 @@ class SimpleServer {
 
   reset() {
     this._routes.clear();
-    let error = new Error('Static Server has been reset');
+    const error = new Error('Static Server has been reset');
-    for (let subscriber of this._requestSubscribers.values())
+    for (const subscriber of this._requestSubscribers.values())
       subscriber[rejectSymbol].call(null, error);
     this._requestSubscribers.clear();
   }
@@ -152,11 +152,11 @@ class SimpleServer {
       else
         throw error;
     });
-    let pathName = url.parse(request.url).path;
+    const pathName = url.parse(request.url).path;
     // Notify request subscriber.
     if (this._requestSubscribers.has(pathName))
       this._requestSubscribers.get(pathName)[fulfillSymbol].call(null, request);
-    let handler = this._routes.get(pathName);
+    const handler = this._routes.get(pathName);
     if (handler)
       handler.call(null, request, response);
     else

test/test.js

@@ -82,9 +82,9 @@ afterAll(SX(async function() {
 
 describe('Browser', function() {
   it('Browser.Options.ignoreHTTPSErrors', SX(async function() {
-    let options = Object.assign({ignoreHTTPSErrors: true}, defaultBrowserOptions);
+    const options = Object.assign({ignoreHTTPSErrors: true}, defaultBrowserOptions);
-    let browser = await puppeteer.launch(options);
+    const browser = await puppeteer.launch(options);
-    let page = await browser.newPage();
+    const page = await browser.newPage();
     let error = null;
     let response = null;
     try {
@@ -97,20 +97,20 @@ describe('Browser', function() {
     browser.close();
   }));
   it('should reject all promises when browser is closed', SX(async function() {
-    let browser = await puppeteer.launch(defaultBrowserOptions);
+    const browser = await puppeteer.launch(defaultBrowserOptions);
-    let page = await browser.newPage();
+    const page = await browser.newPage();
     let error = null;
-    let neverResolves = page.evaluate(() => new Promise(r => {})).catch(e => error = e);
+    const neverResolves = page.evaluate(() => new Promise(r => {})).catch(e => error = e);
     browser.close();
     await neverResolves;
     expect(error.message).toContain('Protocol error');
   }));
   it('Puppeteer.connect', SX(async function() {
-    let originalBrowser = await puppeteer.launch(defaultBrowserOptions);
+    const originalBrowser = await puppeteer.launch(defaultBrowserOptions);
-    let browser = await puppeteer.connect({
+    const browser = await puppeteer.connect({
       browserWSEndpoint: originalBrowser.wsEndpoint()
     });
-    let page = await browser.newPage();
+    const page = await browser.newPage();
     expect(await page.evaluate(() => 7 * 8)).toBe(56);
     originalBrowser.close();
   }));
@@ -144,7 +144,7 @@ describe('Page', function() {
 
   describe('Browser.version', function() {
     it('should return whether we are in headless', SX(async function() {
-      let version = await browser.version();
+      const version = await browser.version();
       expect(version.length).toBeGreaterThan(0);
       expect(version.startsWith('Headless')).toBe(headless);
     }));
@@ -152,8 +152,8 @@ describe('Page', function() {
 
   describe('Page.close', function() {
     it('should reject all promises when page is closed', SX(async function() {
-      let newPage = await browser.newPage();
+      const newPage = await browser.newPage();
-      let neverResolves = newPage.evaluate(() => new Promise(r => {}));
+      const neverResolves = newPage.evaluate(() => new Promise(r => {}));
       newPage.close();
       let error = null;
       try {
@@ -177,11 +177,11 @@ describe('Page', function() {
 
   describe('Page.evaluate', function() {
     it('should work', SX(async function() {
-      let result = await page.evaluate(() => 7 * 3);
+      const result = await page.evaluate(() => 7 * 3);
       expect(result).toBe(21);
     }));
     it('should await promise', SX(async function() {
-      let result = await page.evaluate(() => Promise.resolve(8 * 7));
+      const result = await page.evaluate(() => Promise.resolve(8 * 7));
       expect(result).toBe(56);
     }));
     it('should work from-inside an exposed function', SX(async function() {
@@ -189,7 +189,7 @@ describe('Page', function() {
       await page.exposeFunction('callController', async function(a, b) {
         return await page.evaluate((a, b) => a * b, a, b);
       });
-      let result = await page.evaluate(async function() {
+      const result = await page.evaluate(async function() {
         return await callController(9, 3);
       });
       expect(result).toBe(27);
@@ -206,40 +206,40 @@ describe('Page', function() {
     }));
     it('should return complex objects', SX(async function() {
       const object = {foo: 'bar!'};
-      let result = await page.evaluate(a => a, object);
+      const result = await page.evaluate(a => a, object);
       expect(result).not.toBe(object);
       expect(result).toEqual(object);
     }));
     it('should return NaN', SX(async function() {
-      let result = await page.evaluate(() => NaN);
+      const result = await page.evaluate(() => NaN);
       expect(Object.is(result, NaN)).toBe(true);
     }));
     it('should return -0', SX(async function() {
-      let result = await page.evaluate(() => -0);
+      const result = await page.evaluate(() => -0);
       expect(Object.is(result, -0)).toBe(true);
     }));
     it('should return Infinity', SX(async function() {
-      let result = await page.evaluate(() => Infinity);
+      const result = await page.evaluate(() => Infinity);
       expect(Object.is(result, Infinity)).toBe(true);
     }));
     it('should return -Infinity', SX(async function() {
-      let result = await page.evaluate(() => -Infinity);
+      const result = await page.evaluate(() => -Infinity);
       expect(Object.is(result, -Infinity)).toBe(true);
     }));
     it('should not fail for window object', SX(async function() {
-      let result = await page.evaluate(() => window);
+      const result = await page.evaluate(() => window);
       expect(result).toBe('Window');
     }));
     it('should accept a string', SX(async function() {
-      let result = await page.evaluate('1 + 2');
+      const result = await page.evaluate('1 + 2');
       expect(result).toBe(3);
     }));
     it('should accept a string with semi colons', SX(async function() {
-      let result = await page.evaluate('1 + 5;');
+      const result = await page.evaluate('1 + 5;');
       expect(result).toBe(6);
     }));
     it('should accept a string with comments', SX(async function() {
-      let result = await page.evaluate('2 + 5;\n// do some math!');
+      const result = await page.evaluate('2 + 5;\n// do some math!');
       expect(result).toBe(7);
     }));
   });
@@ -260,13 +260,13 @@ describe('Page', function() {
   });
 
   describe('Frame.evaluate', function() {
-    let FrameUtils = require('./frame-utils');
+    const FrameUtils = require('./frame-utils');
     it('should have different execution contexts', SX(async function() {
       await page.goto(EMPTY_PAGE);
       await FrameUtils.attachFrame(page, 'frame1', EMPTY_PAGE);
       expect(page.frames().length).toBe(2);
-      let frame1 = page.frames()[0];
+      const frame1 = page.frames()[0];
-      let frame2 = page.frames()[1];
+      const frame2 = page.frames()[1];
       await frame1.evaluate(() => window.FOO = 'foo');
       await frame2.evaluate(() => window.FOO = 'bar');
       expect(await frame1.evaluate(() => window.FOO)).toBe('foo');
@@ -274,7 +274,7 @@ describe('Page', function() {
     }));
     it('should execute after cross-site navigation', SX(async function() {
       await page.goto(EMPTY_PAGE);
-      let mainFrame = page.mainFrame();
+      const mainFrame = page.mainFrame();
       expect(await mainFrame.evaluate(() => window.location.href)).toContain('localhost');
       await page.goto(CROSS_PROCESS_PREFIX + '/empty.html');
       expect(await mainFrame.evaluate(() => window.location.href)).toContain('127');
@@ -336,12 +336,12 @@ describe('Page', function() {
   });
 
   describe('Frame.waitForSelector', function() {
-    let FrameUtils = require('./frame-utils');
+    const FrameUtils = require('./frame-utils');
-    let addElement = tag => document.body.appendChild(document.createElement(tag));
+    const addElement = tag => document.body.appendChild(document.createElement(tag));
 
     it('should immediately resolve promise if node exists', SX(async function() {
       await page.goto(EMPTY_PAGE);
-      let frame = page.mainFrame();
+      const frame = page.mainFrame();
       let added = false;
       await frame.waitForSelector('*').then(() => added = true);
       expect(added).toBe(true);
@@ -354,9 +354,9 @@ describe('Page', function() {
 
     it('should resolve promise when node is added', SX(async function() {
       await page.goto(EMPTY_PAGE);
-      let frame = page.mainFrame();
+      const frame = page.mainFrame();
       let added = false;
-      let watchdog = frame.waitForSelector('div').then(() => added = true);
+      const watchdog = frame.waitForSelector('div').then(() => added = true);
       // run nop function..
       await frame.evaluate(() => 42);
       // .. to be sure that waitForSelector promise is not resolved yet.
@@ -370,7 +370,7 @@ describe('Page', function() {
 
     it('should work when node is added through innerHTML', SX(async function() {
       await page.goto(EMPTY_PAGE);
-      let watchdog = page.waitForSelector('h3 div');
+      const watchdog = page.waitForSelector('h3 div');
       await page.evaluate(addElement, 'span');
       await page.evaluate(() => document.querySelector('span').innerHTML = '<h3><div></div></h3>');
       await watchdog;
@@ -379,7 +379,7 @@ describe('Page', function() {
     it('Page.waitForSelector is shortcut for main frame', SX(async function() {
       await page.goto(EMPTY_PAGE);
       await FrameUtils.attachFrame(page, 'frame1', EMPTY_PAGE);
-      let otherFrame = page.frames()[1];
+      const otherFrame = page.frames()[1];
       let added = false;
       page.waitForSelector('div').then(() => added = true);
       await otherFrame.evaluate(addElement, 'div');
@@ -391,8 +391,8 @@ describe('Page', function() {
     it('should run in specified frame', SX(async function() {
       await FrameUtils.attachFrame(page, 'frame1', EMPTY_PAGE);
       await FrameUtils.attachFrame(page, 'frame2', EMPTY_PAGE);
-      let frame1 = page.frames()[1];
+      const frame1 = page.frames()[1];
-      let frame2 = page.frames()[2];
+      const frame2 = page.frames()[2];
       let added = false;
       frame2.waitForSelector('div').then(() => added = true);
       expect(added).toBe(false);
@@ -416,9 +416,9 @@ describe('Page', function() {
     }));
     it('should throw when frame is detached', SX(async function() {
       await FrameUtils.attachFrame(page, 'frame1', EMPTY_PAGE);
-      let frame = page.frames()[1];
+      const frame = page.frames()[1];
       let waitError = null;
-      let waitPromise = frame.waitForSelector('.box').catch(e => waitError = e);
+      const waitPromise = frame.waitForSelector('.box').catch(e => waitError = e);
       await FrameUtils.detachFrame(page, 'frame1');
       await waitPromise;
       expect(waitError).toBeTruthy();
@@ -426,7 +426,7 @@ describe('Page', function() {
     }));
     it('should survive cross-process navigation', SX(async function() {
       let boxFound = false;
-      let waitForSelector = page.waitForSelector('.box').then(() => boxFound = true);
+      const waitForSelector = page.waitForSelector('.box').then(() => boxFound = true);
       await page.goto(EMPTY_PAGE);
       expect(boxFound).toBe(false);
       await page.reload();
@@ -437,7 +437,7 @@ describe('Page', function() {
     }));
     it('should wait for visible', SX(async function() {
       let divFound = false;
-      let waitForSelector = page.waitForSelector('div', {visible: true}).then(() => divFound = true);
+      const waitForSelector = page.waitForSelector('div', {visible: true}).then(() => divFound = true);
       await page.setContent(`<div style='display: none;visibility: hidden'></div>`);
       expect(divFound).toBe(false);
       await page.evaluate(() => document.querySelector('div').style.removeProperty('display'));
@@ -456,7 +456,7 @@ describe('Page', function() {
   describe('Page.waitFor', function() {
     it('should wait for selector', SX(async function() {
       let found = false;
-      let waitFor = page.waitFor('div').then(() => found = true);
+      const waitFor = page.waitFor('div').then(() => found = true);
       await page.goto(EMPTY_PAGE);
       expect(found).toBe(false);
       await page.goto(PREFIX + '/grid.html');
@@ -464,7 +464,7 @@ describe('Page', function() {
       expect(found).toBe(true);
     }));
     it('should timeout', SX(async function() {
-      let startTime = Date.now();
+      const startTime = Date.now();
       const timeout = 42;
       await page.waitFor(timeout);
       expect(Date.now() - startTime).not.toBeLessThan(timeout / 2);
@@ -495,7 +495,7 @@ describe('Page', function() {
       expect(commandArgs).toEqual([5, 'hello', {foo: 'bar'}]);
     }));
     it('should work for different console API calls', SX(async function() {
-      let messages = [];
+      const messages = [];
       page.on('console', msg => messages.push(msg));
       await Promise.all([
         page.evaluate(() => {
@@ -533,7 +533,7 @@ describe('Page', function() {
 
   describe('Page.goto', function() {
     it('should navigate to about:blank', SX(async function() {
-      let response = await page.goto('about:blank');
+      const response = await page.goto('about:blank');
       expect(response).toBe(null);
     }));
     it('should fail when navigating to bad url', SX(async function() {
@@ -607,16 +607,16 @@ describe('Page', function() {
       server.setRoute('/fetch-request-b.js', (req, res) => responses.push(res));
       server.setRoute('/fetch-request-c.js', (req, res) => responses.push(res));
       server.setRoute('/fetch-request-d.js', (req, res) => responses.push(res));
-      let initialFetchResourcesRequested = Promise.all([
+      const initialFetchResourcesRequested = Promise.all([
         server.waitForRequest('/fetch-request-a.js'),
         server.waitForRequest('/fetch-request-b.js'),
         server.waitForRequest('/fetch-request-c.js'),
       ]);
-      let secondFetchResourceRequested = server.waitForRequest('/fetch-request-d.js');
+      const secondFetchResourceRequested = server.waitForRequest('/fetch-request-d.js');
 
       // Navigate to a page which loads immediately and then does a bunch of
       // requests via javascript's fetch method.
-      let navigationPromise = page.goto(PREFIX + '/networkidle.html', {
+      const navigationPromise = page.goto(PREFIX + '/networkidle.html', {
         waitUntil: 'networkidle',
         networkIdleTimeout: 100,
         networkIdleInflight: 0, // Only be idle when there are 0 inflight requests
@@ -636,7 +636,7 @@ describe('Page', function() {
       expect(navigationFinished).toBe(false);
 
       // Respond to initial requests.
-      for (let response of responses) {
+      for (const response of responses) {
         response.statusCode = 404;
         response.end(`File not found`);
       }
@@ -650,7 +650,7 @@ describe('Page', function() {
       expect(navigationFinished).toBe(false);
 
       // Respond to requests.
-      for (let response of responses) {
+      for (const response of responses) {
         response.statusCode = 404;
         response.end(`File not found`);
       }
@@ -660,13 +660,13 @@ describe('Page', function() {
       expect(response.ok).toBe(true);
     }));
     it('should wait for websockets to succeed navigation', SX(async function() {
-      let responses = [];
+      const responses = [];
       // Hold on to the fetch request without answering.
       server.setRoute('/fetch-request.js', (req, res) => responses.push(res));
-      let fetchResourceRequested = server.waitForRequest('/fetch-request.js');
+      const fetchResourceRequested = server.waitForRequest('/fetch-request.js');
       // Navigate to a page which loads immediately and then opens a bunch of
       // websocket connections and then a fetch request.
-      let navigationPromise = page.goto(PREFIX + '/websocket.html', {
+      const navigationPromise = page.goto(PREFIX + '/websocket.html', {
         waitUntil: 'networkidle',
         networkIdleTimeout: 100,
         networkIdleInflight: 0, // Only be idle when there are 0 inflight requests/connections
@@ -686,7 +686,7 @@ describe('Page', function() {
       expect(navigationFinished).toBe(false);
 
       // Respond to the request.
-      for (let response of responses) {
+      for (const response of responses) {
         response.statusCode = 404;
         response.end(`File not found`);
       }
@@ -704,18 +704,18 @@ describe('Page', function() {
       expect(warning).toBe(null);
     }));
     it('should navigate to dataURL and fire dataURL requests', SX(async function() {
-      let requests = [];
+      const requests = [];
       page.on('request', request => requests.push(request));
-      let dataURL = 'data:text/html,<div>yo</div>';
+      const dataURL = 'data:text/html,<div>yo</div>';
-      let response = await page.goto(dataURL);
+      const response = await page.goto(dataURL);
       expect(response.status).toBe(200);
       expect(requests.length).toBe(1);
       expect(requests[0].url).toBe(dataURL);
     }));
     it('should navigate to URL with hash and fire requests without hash', SX(async function() {
-      let requests = [];
+      const requests = [];
       page.on('request', request => requests.push(request));
-      let response = await page.goto(EMPTY_PAGE + '#hash');
+      const response = await page.goto(EMPTY_PAGE + '#hash');
       expect(response.status).toBe(200);
       expect(response.url).toBe(EMPTY_PAGE);
       expect(requests.length).toBe(1);
@@ -759,7 +759,7 @@ describe('Page', function() {
       await page.exposeFunction('compute', function(a, b) {
         return a * b;
       });
-      let result = await page.evaluate(async function() {
+      const result = await page.evaluate(async function() {
         return await compute(9, 4);
       });
       expect(result).toBe(36);
@@ -770,7 +770,7 @@ describe('Page', function() {
       });
 
       await page.goto(EMPTY_PAGE);
-      let result = await page.evaluate(async function() {
+      const result = await page.evaluate(async function() {
         return await compute(9, 4);
       });
       expect(result).toBe(36);
@@ -780,7 +780,7 @@ describe('Page', function() {
         return Promise.resolve(a * b);
       });
 
-      let result = await page.evaluate(async function() {
+      const result = await page.evaluate(async function() {
         return await compute(3, 5);
       });
       expect(result).toBe(15);
@@ -829,7 +829,7 @@ describe('Page', function() {
     it('should amend HTTP headers', SX(async function() {
       await page.setRequestInterceptionEnabled(true);
       page.on('request', request => {
-        let headers = new Map(request.headers);
+        const headers = new Map(request.headers);
         headers.set('foo', 'bar');
         request.continue({ headers });
       });
@@ -859,7 +859,7 @@ describe('Page', function() {
       server.setRedirect('/non-existing-page-2.html', '/non-existing-page-3.html');
       server.setRedirect('/non-existing-page-3.html', '/non-existing-page-4.html');
       server.setRedirect('/non-existing-page-4.html', '/empty.html');
-      let response = await page.goto(PREFIX + '/non-existing-page.html');
+      const response = await page.goto(PREFIX + '/non-existing-page.html');
       expect(response.status).toBe(200);
       expect(response.url).toContain('empty.html');
     }));
@@ -874,7 +874,7 @@ describe('Page', function() {
           request.continue();
       });
       await page.goto(EMPTY_PAGE);
-      let result = await page.evaluate(async() => {
+      const result = await page.evaluate(async() => {
         try {
           await fetch('/non-existing.json');
         } catch (e) {
@@ -895,7 +895,7 @@ describe('Page', function() {
         spinner ? request.abort() : request.continue();
         spinner = !spinner;
       });
-      let results = await page.evaluate(() => Promise.all([
+      const results = await page.evaluate(() => Promise.all([
         fetch('/zzz').then(response => response.text()).catch(e => 'FAILED'),
         fetch('/zzz').then(response => response.text()).catch(e => 'FAILED'),
         fetch('/zzz').then(response => response.text()).catch(e => 'FAILED'),
@@ -904,25 +904,25 @@ describe('Page', function() {
     }));
     it('should navigate to dataURL and fire dataURL requests', SX(async function() {
       await page.setRequestInterceptionEnabled(true);
-      let requests = [];
+      const requests = [];
       page.on('request', request => {
         requests.push(request);
         request.continue();
       });
-      let dataURL = 'data:text/html,<div>yo</div>';
+      const dataURL = 'data:text/html,<div>yo</div>';
-      let response = await page.goto(dataURL);
+      const response = await page.goto(dataURL);
       expect(response.status).toBe(200);
       expect(requests.length).toBe(1);
       expect(requests[0].url).toBe(dataURL);
     }));
     it('should navigate to URL with hash and and fire requests without hash', SX(async function() {
       await page.setRequestInterceptionEnabled(true);
-      let requests = [];
+      const requests = [];
       page.on('request', request => {
         requests.push(request);
         request.continue();
       });
-      let response = await page.goto(EMPTY_PAGE + '#hash');
+      const response = await page.goto(EMPTY_PAGE + '#hash');
       expect(response.status).toBe(200);
       expect(response.url).toBe(EMPTY_PAGE);
       expect(requests.length).toBe(1);
@@ -947,14 +947,14 @@ describe('Page', function() {
         expect(dialog.message()).toBe('question?');
         dialog.accept('answer!');
       });
-      let result = await page.evaluate(() => prompt('question?', 'yes.'));
+      const result = await page.evaluate(() => prompt('question?', 'yes.'));
       expect(result).toBe('answer!');
     }));
     it('should dismiss the prompt', SX(async function() {
       page.on('dialog', dialog => {
         dialog.dismiss();
       });
-      let result = await page.evaluate(() => prompt('question?'));
+      const result = await page.evaluate(() => prompt('question?'));
       expect(result).toBe(null);
     }));
   });
@@ -971,7 +971,7 @@ describe('Page', function() {
 
   describe('Page.Events.Request', function() {
     it('should fire', SX(async function() {
-      let requests = [];
+      const requests = [];
       page.on('request', request => requests.push(request));
       await page.goto(EMPTY_PAGE);
       expect(requests.length).toBe(1);
@@ -980,7 +980,7 @@ describe('Page', function() {
   });
 
   describe('Frame Management', function() {
-    let FrameUtils = require('./frame-utils');
+    const FrameUtils = require('./frame-utils');
     it('should handle nested frames', SX(async function() {
       await page.goto(PREFIX + '/frames/nested-frames.html');
       expect(FrameUtils.dumpFrames(page.mainFrame())).toBeGolden('nested-frames.txt');
@@ -988,21 +988,21 @@ describe('Page', function() {
     it('should send events when frames are manipulated dynamically', SX(async function() {
       await page.goto(EMPTY_PAGE);
       // validate frameattached events
-      let attachedFrames = [];
+      const attachedFrames = [];
       page.on('frameattached', frame => attachedFrames.push(frame));
       await FrameUtils.attachFrame(page, 'frame1', './assets/frame.html');
       expect(attachedFrames.length).toBe(1);
       expect(attachedFrames[0].url()).toContain('/assets/frame.html');
 
       // validate framenavigated events
-      let navigatedFrames = [];
+      const navigatedFrames = [];
       page.on('framenavigated', frame => navigatedFrames.push(frame));
       await FrameUtils.navigateFrame(page, 'frame1', './empty.html');
       expect(navigatedFrames.length).toBe(1);
       expect(navigatedFrames[0].url()).toContain('/empty.html');
 
       // validate framedetached events
-      let detachedFrames = [];
+      const detachedFrames = [];
       page.on('framedetached', frame => detachedFrames.push(frame));
       await FrameUtils.detachFrame(page, 'frame1');
       expect(detachedFrames.length).toBe(1);
@@ -1010,7 +1010,7 @@ describe('Page', function() {
     }));
     it('should persist mainFrame on cross-process navigation', SX(async function() {
       await page.goto(EMPTY_PAGE);
-      let mainFrame = page.mainFrame();
+      const mainFrame = page.mainFrame();
       await page.goto('http://127.0.0.1:' + PORT + '/empty.html');
       expect(page.mainFrame() === mainFrame).toBeTruthy();
     }));
@@ -1044,7 +1044,7 @@ describe('Page', function() {
     it('should report frame.name()', SX(async function() {
       await FrameUtils.attachFrame(page, 'theFrameId', EMPTY_PAGE);
       await page.evaluate(url => {
-        let frame = document.createElement('iframe');
+        const frame = document.createElement('iframe');
         frame.name = 'theFrameName';
         frame.src = url;
         document.body.appendChild(frame);
@@ -1066,11 +1066,11 @@ describe('Page', function() {
   describe('Page.$', function() {
     it('should query existing element', SX(async function() {
       await page.setContent('<section>test</section>');
-      let element = await page.$('section');
+      const element = await page.$('section');
       expect(element).toBeTruthy();
     }));
     it('should return null for non-existing element', SX(async function() {
-      let element = await page.$('non-existing-element');
+      const element = await page.$('non-existing-element');
       expect(element).toBe(null);
     }));
   });
@@ -1078,20 +1078,20 @@ describe('Page', function() {
   describe('ElementHandle.evaluate', function() {
     it('should work', SX(async function() {
       await page.setContent('<section>42</section>');
-      let element = await page.$('section');
+      const element = await page.$('section');
-      let text = await element.evaluate(e => e.textContent);
+      const text = await element.evaluate(e => e.textContent);
       expect(text).toBe('42');
     }));
     it('should await promise if any', SX(async function() {
       await page.setContent('<section>39</section>');
-      let element = await page.$('section');
+      const element = await page.$('section');
-      let text = await element.evaluate(e => Promise.resolve(e.textContent));
+      const text = await element.evaluate(e => Promise.resolve(e.textContent));
       expect(text).toBe('39');
     }));
     it('should throw if underlying page got closed', SX(async function() {
-      let otherPage = await browser.newPage();
+      const otherPage = await browser.newPage();
       await otherPage.setContent('<section>88</section>');
-      let element = await otherPage.$('section');
+      const element = await otherPage.$('section');
       expect(element).toBeTruthy();
       await otherPage.close();
       let error = null;
@@ -1104,7 +1104,7 @@ describe('Page', function() {
     }));
     it('should throw if underlying element was disposed', SX(async function() {
       await page.setContent('<section>39</section>');
-      let element = await page.$('section');
+      const element = await page.$('section');
       expect(element).toBeTruthy();
       await element.dispose();
       let error = null;
@@ -1120,7 +1120,7 @@ describe('Page', function() {
   describe('ElementHandle.click', function() {
     it('should work', SX(async function() {
       await page.goto(PREFIX + '/input/button.html');
-      let button = await page.$('button');
+      const button = await page.$('button');
       await button.click('button');
       expect(await page.evaluate(() => result)).toBe('Clicked');
     }));
@@ -1129,7 +1129,7 @@ describe('Page', function() {
   describe('ElementHandle.hover', function() {
     it('should work', SX(async function() {
       await page.goto(PREFIX + '/input/scrollable.html');
-      let button = await page.$('#button-6');
+      const button = await page.$('#button-6');
       await button.hover();
       expect(await page.evaluate(() => document.querySelector('button:hover').id)).toBe('button-6');
     }));
@@ -1173,12 +1173,12 @@ describe('Page', function() {
     it('should upload the file', SX(async function(){
       await page.goto(PREFIX + '/input/fileupload.html');
       const filePath = path.relative(process.cwd(), __dirname + '/assets/file-to-upload.txt');
-      let input = await page.$('input');
+      const input = await page.$('input');
       await input.uploadFile(filePath);
       expect(await input.evaluate(e => e.files[0].name)).toBe('file-to-upload.txt');
       expect(await input.evaluate(e => {
-        let reader = new FileReader();
+        const reader = new FileReader();
-        let promise = new Promise(fulfill => reader.onload = fulfill);
+        const promise = new Promise(fulfill => reader.onload = fulfill);
         reader.readAsText(e.files[0]);
         return promise.then(() => reader.result);
       })).toBe('contents of the file');
@@ -1221,9 +1221,9 @@ describe('Page', function() {
     }));
     it('should report shiftKey', SX(async function(){
       await page.goto(PREFIX + '/input/keyboard.html');
-      let keyboard = page.keyboard;
+      const keyboard = page.keyboard;
-      let codeForKey = {'Shift': 16, 'Alt': 18, 'Meta': 91, 'Control': 17};
+      const codeForKey = {'Shift': 16, 'Alt': 18, 'Meta': 91, 'Control': 17};
-      for (let modifierKey in codeForKey) {
+      for (const modifierKey in codeForKey) {
         await keyboard.down(modifierKey);
         expect(await page.evaluate(() => getResult())).toBe('Keydown: ' + modifierKey + ' ' + codeForKey[modifierKey] + ' [' + modifierKey + ']');
         await keyboard.down('!');
@@ -1236,7 +1236,7 @@ describe('Page', function() {
     }));
     it('should report multiple modifiers', SX(async function(){
       await page.goto(PREFIX + '/input/keyboard.html');
-      let keyboard = page.keyboard;
+      const keyboard = page.keyboard;
       await keyboard.down('Control');
       expect(await page.evaluate(() => getResult())).toBe('Keydown: Control 17 [Control]');
       await keyboard.down('Meta');
@@ -1265,7 +1265,7 @@ describe('Page', function() {
     }));
     it('should send propery codes while typing with shift', SX(async function(){
       await page.goto(PREFIX + '/input/keyboard.html');
-      let keyboard = page.keyboard;
+      const keyboard = page.keyboard;
       await keyboard.down('Shift');
       await page.type('~');
       expect(await page.evaluate(() => getResult())).toBe(
@@ -1292,7 +1292,7 @@ describe('Page', function() {
       expect(await page.evaluate(() => textarea.value)).toBe('He Wrd!');
     }));
     it('keyboard.modifiers()', SX(async function(){
-      let keyboard = page.keyboard;
+      const keyboard = page.keyboard;
       expect(keyboard._modifiers).toBe(0);
       await keyboard.down('Shift');
       expect(keyboard._modifiers).toBe(8);
@@ -1304,13 +1304,13 @@ describe('Page', function() {
     }));
     it('should resize the textarea', SX(async function(){
       await page.goto(PREFIX + '/input/textarea.html');
-      let {x, y, width, height} = await page.evaluate(dimensions);
+      const {x, y, width, height} = await page.evaluate(dimensions);
-      let mouse = page.mouse;
+      const mouse = page.mouse;
       await mouse.move(x + width - 4, y + height - 4);
       await mouse.down();
       await mouse.move(x + width + 100, y + height + 100);
       await mouse.up();
-      let newDimensions = await page.evaluate(dimensions);
+      const newDimensions = await page.evaluate(dimensions);
       expect(newDimensions.width).toBe(width + 104);
       expect(newDimensions.height).toBe(height + 104);
     }));
@@ -1324,7 +1324,7 @@ describe('Page', function() {
     it('should click a partially obscured button', SX(async function() {
       await page.goto(PREFIX + '/input/button.html');
       await page.evaluate(() => {
-        let button = document.querySelector('button');
+        const button = document.querySelector('button');
         button.textContent = 'Some really long text that will go offscreen';
         button.style.position = 'absolute';
         button.style.left = '368px';
@@ -1335,10 +1335,10 @@ describe('Page', function() {
     it('should select the text with mouse', SX(async function(){
       await page.goto(PREFIX + '/input/textarea.html');
       await page.focus('textarea');
-      let text = 'This is the text that we are going to try to select. Let\'s see how it goes.';
+      const text = 'This is the text that we are going to try to select. Let\'s see how it goes.';
       await page.type(text);
       await page.evaluate(() => document.querySelector('textarea').scrollTop = 0);
-      let {x, y} = await page.evaluate(dimensions);
+      const {x, y} = await page.evaluate(dimensions);
       await page.mouse.move(x + 2,y + 2);
       await page.mouse.down();
       await page.mouse.move(100,100);
@@ -1348,7 +1348,7 @@ describe('Page', function() {
     it('should select the text by triple clicking', SX(async function(){
       await page.goto(PREFIX + '/input/textarea.html');
       await page.focus('textarea');
-      let text = 'This is the text that we are going to try to select. Let\'s see how it goes.';
+      const text = 'This is the text that we are going to try to select. Let\'s see how it goes.';
       await page.type(text);
       await page.click('textarea');
       await page.click('textarea', {clickCount: 2});
@@ -1372,8 +1372,8 @@ describe('Page', function() {
     it('should set modifier keys on click', SX(async function(){
       await page.goto(PREFIX + '/input/scrollable.html');
       await page.evaluate(() => document.querySelector('#button-3').addEventListener('mousedown', e => window.lastEvent = e, true));
-      let modifiers = {'Shift': 'shiftKey', 'Control': 'ctrlKey', 'Alt': 'altKey', 'Meta': 'metaKey'};
+      const modifiers = {'Shift': 'shiftKey', 'Control': 'ctrlKey', 'Alt': 'altKey', 'Meta': 'metaKey'};
-      for (let modifier in modifiers) {
+      for (const modifier in modifiers) {
         await page.keyboard.down(modifier);
         await page.click('#button-3');
         if (!(await page.evaluate(mod => window.lastEvent[mod], modifiers[modifier])))
@@ -1381,7 +1381,7 @@ describe('Page', function() {
         await page.keyboard.up(modifier);
       }
       await page.click('#button-3');
-      for (let modifier in modifiers) {
+      for (const modifier in modifiers) {
         if ((await page.evaluate(mod => window.lastEvent[mod], modifiers[modifier])))
           fail(modifiers[modifier] + ' should be false');
       }
@@ -1402,7 +1402,7 @@ describe('Page', function() {
       await page.click('a');
     }));
     function dimensions() {
-      let rect = document.querySelector('textarea').getBoundingClientRect();
+      const rect = document.querySelector('textarea').getBoundingClientRect();
       return {
         x: rect.left,
         y: rect.top,
@@ -1417,7 +1417,7 @@ describe('Page', function() {
       expect(await page.evaluate(() => navigator.userAgent)).toContain('Mozilla');
       page.setUserAgent('foobar');
       page.goto(EMPTY_PAGE);
-      let request = await server.waitForRequest('/empty.html');
+      const request = await server.waitForRequest('/empty.html');
       expect(request.headers['user-agent']).toBe('foobar');
     }));
     it('should emulate device user-agent', SX(async function() {
@@ -1433,7 +1433,7 @@ describe('Page', function() {
         foo: 'bar'
       })));
       page.goto(EMPTY_PAGE);
-      let request = await server.waitForRequest('/empty.html');
+      const request = await server.waitForRequest('/empty.html');
       expect(request.headers['foo']).toBe('bar');
     }));
   });
@@ -1441,26 +1441,26 @@ describe('Page', function() {
     const expectedOutput = '<html><head></head><body><div>hello</div></body></html>';
     it('should work', SX(async function() {
       await page.setContent('<div>hello</div>');
-      let result = await page.content();
+      const result = await page.content();
       expect(result).toBe(expectedOutput);
     }));
     it('should work with doctype', SX(async function() {
       const doctype = '<!DOCTYPE html>';
       await page.setContent(`${doctype}<div>hello</div>`);
-      let result = await page.content();
+      const result = await page.content();
       expect(result).toBe(`${doctype}${expectedOutput}`);
     }));
     it('should work with HTML 4 doctype', SX(async function() {
       const doctype = '<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" ' +
         '"http://www.w3.org/TR/html4/strict.dtd">';
       await page.setContent(`${doctype}<div>hello</div>`);
-      let result = await page.content();
+      const result = await page.content();
       expect(result).toBe(`${doctype}${expectedOutput}`);
     }));
   });
   describe('Network Events', function() {
     it('Page.Events.Request', SX(async function() {
-      let requests = [];
+      const requests = [];
       page.on('request', request => requests.push(request));
       await page.goto(EMPTY_PAGE);
       expect(requests.length).toBe(1);
@@ -1478,7 +1478,7 @@ describe('Page', function() {
       expect(request.postData).toBe('{"foo":"bar"}');
     }));
     it('Page.Events.Response', SX(async function() {
-      let responses = [];
+      const responses = [];
       page.on('response', response => responses.push(response));
       await page.goto(EMPTY_PAGE);
       expect(responses.length).toBe(1);
@@ -1519,7 +1519,7 @@ describe('Page', function() {
       expect(pageResponse.status).toBe(200);
       expect(requestFinished).toBe(false);
 
-      let responseText = pageResponse.text();
+      const responseText = pageResponse.text();
       // Write part of the response and wait for it to be flushed.
       await new Promise(x => serverResponse.write('wor', x));
       // Finish response.
@@ -1534,7 +1534,7 @@ describe('Page', function() {
         else
           request.continue();
       });
-      let failedRequests = [];
+      const failedRequests = [];
       page.on('requestfailed', request => failedRequests.push(request));
       await page.goto(PREFIX + '/one-style.html');
       expect(failedRequests.length).toBe(1);
@@ -1542,7 +1542,7 @@ describe('Page', function() {
       expect(failedRequests[0].response()).toBe(null);
     }));
     it('Page.Events.RequestFinished', SX(async function() {
-      let requests = [];
+      const requests = [];
       page.on('requestfinished', request => requests.push(request));
       await page.goto(EMPTY_PAGE);
       expect(requests.length).toBe(1);
@@ -1550,7 +1550,7 @@ describe('Page', function() {
       expect(requests[0].response()).toBeTruthy();
     }));
     it('should fire events in proper order', SX(async function() {
-      let events = [];
+      const events = [];
       page.on('request', request => events.push('request'));
       page.on('response', response => events.push('response'));
       page.on('requestfinished', request => events.push('requestfinished'));
@@ -1558,7 +1558,7 @@ describe('Page', function() {
       expect(events).toEqual(['request', 'response', 'requestfinished']);
     }));
     it('should support redirects', SX(async function() {
-      let events = [];
+      const events = [];
       page.on('request', request => events.push(`${request.method} ${request.url}`));
       page.on('response', response => events.push(`${response.status} ${response.url}`));
       page.on('requestfinished', request => events.push(`DONE ${request.url}`));
@@ -1618,7 +1618,7 @@ describe('Page', function() {
 
       function dispatchTouch() {
         let fulfill;
-        let promise = new Promise(x => fulfill = x);
+        const promise = new Promise(x => fulfill = x);
         window.ontouchstart = function(e) {
           fulfill('Recieved touch');
         };
@@ -1692,13 +1692,13 @@ describe('Page', function() {
       fs.unlinkSync(outputFile);
     }));
     it('should default to printing in Letter format', SX(async function() {
-      let pages = await getPDFPages(await page.pdf());
+      const pages = await getPDFPages(await page.pdf());
       expect(pages.length).toBe(1);
       expect(pages[0].width).toBeCloseTo(8.5, 2);
       expect(pages[0].height).toBeCloseTo(11, 2);
     }));
     it('should support setting custom format', SX(async function() {
-      let pages = await getPDFPages(await page.pdf({
+      const pages = await getPDFPages(await page.pdf({
         format: 'a4'
       }));
       expect(pages.length).toBe(1);
@@ -1706,7 +1706,7 @@ describe('Page', function() {
       expect(pages[0].height).toBeCloseTo(11.7, 1);
     }));
     it('should support setting paper width and height', SX(async function() {
-      let pages = await getPDFPages(await page.pdf({
+      const pages = await getPDFPages(await page.pdf({
         width: '10in',
         height: '10in',
       }));
@@ -1719,7 +1719,7 @@ describe('Page', function() {
       // Define width and height in CSS pixels.
       const width = 50 * 5 + 1;
       const height = 50 * 5 + 1;
-      let pages = await getPDFPages(await page.pdf({width, height}));
+      const pages = await getPDFPages(await page.pdf({width, height}));
       expect(pages.length).toBe(8);
       expect(pages[0].width).toBeCloseTo(cssPixelsToInches(width), 2);
       expect(pages[0].height).toBeCloseTo(cssPixelsToInches(height), 2);
@@ -1729,7 +1729,7 @@ describe('Page', function() {
       // Define width and height in CSS pixels.
       const width = 50 * 5 + 1;
       const height = 50 * 5 + 1;
-      let pages = await getPDFPages(await page.pdf({width, height, pageRanges: '1,4-7'}));
+      const pages = await getPDFPages(await page.pdf({width, height, pageRanges: '1,4-7'}));
       expect(pages.length).toBe(5);
     }));
     it('should throw if format is unknown', SX(async function() {
@@ -1777,13 +1777,13 @@ describe('Page', function() {
     it('should work', SX(async function() {
       await page.setViewport({width: 500, height: 500});
       await page.goto(PREFIX + '/grid.html');
-      let screenshot = await page.screenshot();
+      const screenshot = await page.screenshot();
       expect(screenshot).toBeGolden('screenshot-sanity.png');
     }));
     it('should clip rect', SX(async function() {
       await page.setViewport({width: 500, height: 500});
       await page.goto(PREFIX + '/grid.html');
-      let screenshot = await page.screenshot({
+      const screenshot = await page.screenshot({
         clip: {
           x: 50,
           y: 100,
@@ -1796,7 +1796,7 @@ describe('Page', function() {
     it('should work for offscreen clip', SX(async function() {
       await page.setViewport({width: 500, height: 500});
       await page.goto(PREFIX + '/grid.html');
-      let screenshot = await page.screenshot({
+      const screenshot = await page.screenshot({
         clip: {
           x: 50,
           y: 600,
@@ -1809,7 +1809,7 @@ describe('Page', function() {
     it('should run in parallel', SX(async function() {
       await page.setViewport({width: 500, height: 500});
       await page.goto(PREFIX + '/grid.html');
-      let promises = [];
+      const promises = [];
       for (let i = 0; i < 3; ++i) {
         promises.push(page.screenshot({
           clip: {
@@ -1820,28 +1820,28 @@ describe('Page', function() {
           }
         }));
       }
-      let screenshots = await Promise.all(promises);
+      const screenshots = await Promise.all(promises);
       expect(screenshots[1]).toBeGolden('grid-cell-1.png');
     }));
     it('should take fullPage screenshots', SX(async function() {
       await page.setViewport({width: 500, height: 500});
       await page.goto(PREFIX + '/grid.html');
-      let screenshot = await page.screenshot({
+      const screenshot = await page.screenshot({
         fullPage: true
       });
       expect(screenshot).toBeGolden('screenshot-grid-fullpage.png');
     }));
     it('should run in parallel in multiple pages', SX(async function() {
       const N = 2;
-      let pages = await Promise.all(Array(N).fill(0).map(async() => {
+      const pages = await Promise.all(Array(N).fill(0).map(async() => {
-        let page = await browser.newPage();
+        const page = await browser.newPage();
         await page.goto(PREFIX + '/grid.html');
         return page;
       }));
-      let promises = [];
+      const promises = [];
       for (let i = 0; i < N; ++i)
         promises.push(pages[i].screenshot({ clip: { x: 50 * i, y: 0, width: 50, height: 50 } }));
-      let screenshots = await Promise.all(promises);
+      const screenshots = await Promise.all(promises);
       for (let i = 0; i < N; ++i)
         expect(screenshots[i]).toBeGolden(`grid-cell-${i}.png`);
       await Promise.all(pages.map(page => page.close()));
@@ -1849,13 +1849,13 @@ describe('Page', function() {
     it('should allow transparency', SX(async function() {
       await page.setViewport({ width: 100, height: 100 });
       await page.goto(EMPTY_PAGE);
-      let screenshot = await page.screenshot({omitBackground:true});
+      const screenshot = await page.screenshot({omitBackground:true});
       expect(screenshot).toBeGolden('transparent.png');
     }));
   });
 
   describe('Tracing', function() {
-    let outputFile = path.join(__dirname, 'assets', 'trace.json');
+    const outputFile = path.join(__dirname, 'assets', 'trace.json');
     afterEach(function() {
       fs.unlinkSync(outputFile);
     });
@@ -1867,7 +1867,7 @@ describe('Page', function() {
     }));
     it('should throw if tracing on two pages', SX(async function() {
       await page.tracing.start({path: outputFile});
-      let newPage = await browser.newPage();
+      const newPage = await browser.newPage();
       let error = null;
       try {
         await newPage.tracing.start({path: outputFile});
@@ -1883,12 +1883,12 @@ describe('Page', function() {
 
 if (process.env.COVERAGE) {
   describe('COVERAGE', function(){
-    let coverage = helper.publicAPICoverage();
+    const coverage = helper.publicAPICoverage();
-    let disabled = new Set();
+    const disabled = new Set();
     if (!headless)
       disabled.add('page.pdf');
 
-    for (let method of coverage.keys()) {
+    for (const method of coverage.keys()) {
       (disabled.has(method) ? xit : it)(`public api '${method}' should be called`, SX(async function(){
         expect(coverage.get(method)).toBe(true);
       }));
@@ -1903,7 +1903,7 @@ if (process.env.COVERAGE) {
  */
 function waitForEvents(emitter, eventName, eventCount = 1) {
   let fulfill;
-  let promise = new Promise(x => fulfill = x);
+  const promise = new Promise(x => fulfill = x);
   emitter.on(eventName, onEvent);
   return promise;
 
@@ -1925,10 +1925,10 @@ async function getPDFPages(pdfBuffer) {
   PDFJS.disableWorker = true;
   const data = new Uint8Array(pdfBuffer);
   const doc = await PDFJS.getDocument(data);
-  let pages = [];
+  const pages = [];
   for (let i = 0; i < doc.numPages; ++i) {
-    let page = await doc.getPage(i + 1);
+    const page = await doc.getPage(i + 1);
-    let viewport = page.getViewport(1);
+    const viewport = page.getViewport(1);
     // Viewport width and height is in PDF points, which is
     // 1/72 of an inch.
     pages.push({

utils/ChromiumDownloader.js

@@ -44,7 +44,7 @@ module.exports = {
    * @return {string}
    */
   currentPlatform: function() {
-    let platform = os.platform();
+    const platform = os.platform();
     if (platform === 'darwin')
       return 'mac';
     if (platform === 'linux')
@@ -61,15 +61,15 @@ module.exports = {
    */
   canDownloadRevision: function(platform, revision) {
     console.assert(downloadURLs[platform], 'Unknown platform: ' + platform);
-    let url = URL.parse(util.format(downloadURLs[platform], revision));
+    const url = URL.parse(util.format(downloadURLs[platform], revision));
-    let options = {
+    const options = {
       method: 'HEAD',
       host: url.host,
       path: url.pathname,
     };
     let resolve;
-    let promise = new Promise(x => resolve = x);
+    const promise = new Promise(x => resolve = x);
-    let request = https.request(options, response => {
+    const request = https.request(options, response => {
       resolve(response.statusCode === 200);
     });
     request.on('error', error => {
@@ -90,8 +90,8 @@ module.exports = {
     let url = downloadURLs[platform];
     console.assert(url, `Unsupported platform: ${platform}`);
     url = util.format(url, revision);
-    let zipPath = path.join(DOWNLOADS_FOLDER, `download-${platform}-${revision}.zip`);
+    const zipPath = path.join(DOWNLOADS_FOLDER, `download-${platform}-${revision}.zip`);
-    let folderPath = getFolderPath(platform, revision);
+    const folderPath = getFolderPath(platform, revision);
     if (fs.existsSync(folderPath))
       return;
     try {
@@ -111,7 +111,7 @@ module.exports = {
   downloadedRevisions: function() {
     if (!fs.existsSync(DOWNLOADS_FOLDER))
       return [];
-    let fileNames = fs.readdirSync(DOWNLOADS_FOLDER);
+    const fileNames = fs.readdirSync(DOWNLOADS_FOLDER);
     return fileNames.map(fileName => parseFolderPath(fileName)).filter(revision => !!revision);
   },
 
@@ -133,7 +133,7 @@ module.exports = {
    */
   revisionInfo: function(platform, revision) {
     console.assert(downloadURLs[platform], `Unsupported platform: ${platform}`);
-    let folderPath = getFolderPath(platform, revision);
+    const folderPath = getFolderPath(platform, revision);
     let executablePath = '';
     if (platform === 'mac')
       executablePath = path.join(folderPath, 'chrome-mac', 'Chromium.app', 'Contents', 'MacOS', 'Chromium');
@@ -166,11 +166,11 @@ function getFolderPath(platform, revision) {
  * @return {?{platform: string, revision: string}}
  */
 function parseFolderPath(folderPath) {
-  let name = path.basename(folderPath);
+  const name = path.basename(folderPath);
-  let splits = name.split('-');
+  const splits = name.split('-');
   if (splits.length !== 2)
     return null;
-  let [platform, revision] = splits;
+  const [platform, revision] = splits;
   if (!downloadURLs[platform])
     return null;
   return {platform, revision};
@@ -184,20 +184,20 @@ function parseFolderPath(folderPath) {
  */
 function downloadFile(url, destinationPath, progressCallback) {
   let fulfill, reject;
-  let promise = new Promise((x, y) => { fulfill = x; reject = y; });
+  const promise = new Promise((x, y) => { fulfill = x; reject = y; });
-  let request = https.get(url, response => {
+  const request = https.get(url, response => {
     if (response.statusCode !== 200) {
-      let error = new Error(`Download failed: server returned code ${response.statusCode}. URL: ${url}`);
+      const error = new Error(`Download failed: server returned code ${response.statusCode}. URL: ${url}`);
       // consume response data to free up memory
       response.resume();
       reject(error);
       return;
     }
-    let file = fs.createWriteStream(destinationPath);
+    const file = fs.createWriteStream(destinationPath);
     file.on('finish', () => fulfill());
     file.on('error', error => reject(error));
     response.pipe(file);
-    let totalBytes = parseInt(response.headers['content-length'], 10);
+    const totalBytes = parseInt(response.headers['content-length'], 10);
     if (progressCallback)
       response.on('data', onData.bind(null, totalBytes));
   });

utils/check_availability.js

@@ -59,8 +59,8 @@ Running command without arguments will check against omahaproxy revisions.`);
   return;
 }
 
-let fromRevision = parseInt(process.argv[2], 10);
+const fromRevision = parseInt(process.argv[2], 10);
-let toRevision = parseInt(process.argv[3], 10);
+const toRevision = parseInt(process.argv[3], 10);
 checkRangeAvailability(fromRevision, toRevision);
 
 /**
@@ -68,23 +68,23 @@ checkRangeAvailability(fromRevision, toRevision);
  */
 async function checkOmahaProxyAvailability() {
   console.log('Fetching revisions from ' + OMAHA_PROXY);
-  let platforms = await loadJSON(OMAHA_PROXY);
+  const platforms = await loadJSON(OMAHA_PROXY);
   if (!platforms) {
     console.error('ERROR: failed to fetch chromium revisions from omahaproxy.');
     return;
   }
-  let table = new Table([27, 7, 7, 7, 7]);
+  const table = new Table([27, 7, 7, 7, 7]);
   table.drawRow([''].concat(Downloader.supportedPlatforms()));
-  for (let platform of platforms) {
+  for (const platform of platforms) {
     // Trust only to the main platforms.
     if (platform.os !== 'mac' && platform.os !== 'win' && platform.os !== 'win64' && platform.os !== 'linux')
       continue;
-    let osName = platform.os === 'win' ? 'win32' : platform.os;
+    const osName = platform.os === 'win' ? 'win32' : platform.os;
-    for (let version of platform.versions) {
+    for (const version of platform.versions) {
       if (version.channel !== 'dev' && version.channel !== 'beta' && version.channel !== 'canary' && version.channel !== 'stable')
         continue;
-      let revisionName = padLeft('[' + osName + ' ' + version.channel + ']', 15);
+      const revisionName = padLeft('[' + osName + ' ' + version.channel + ']', 15);
-      let revision = parseInt(version.branch_base_position, 10);
+      const revision = parseInt(version.branch_base_position, 10);
       await checkAndDrawRevisionAvailability(table, revisionName, revision);
     }
   }
@@ -96,9 +96,9 @@ async function checkOmahaProxyAvailability() {
  * @return {!Promise}
  */
 async function checkRangeAvailability(fromRevision, toRevision) {
-  let table = new Table([10, 7, 7, 7, 7]);
+  const table = new Table([10, 7, 7, 7, 7]);
   table.drawRow([''].concat(Downloader.supportedPlatforms()));
-  let inc = fromRevision < toRevision ? 1 : -1;
+  const inc = fromRevision < toRevision ? 1 : -1;
   for (let revision = fromRevision; revision !== toRevision; revision += inc)
     await checkAndDrawRevisionAvailability(table, '', revision);
 }
@@ -110,15 +110,15 @@ async function checkRangeAvailability(fromRevision, toRevision) {
  * @return {!Promise}
  */
 async function checkAndDrawRevisionAvailability(table, name, revision) {
-  let promises = [];
+  const promises = [];
-  for (let platform of Downloader.supportedPlatforms())
+  for (const platform of Downloader.supportedPlatforms())
     promises.push(Downloader.canDownloadRevision(platform, revision));
-  let availability = await Promise.all(promises);
+  const availability = await Promise.all(promises);
-  let allAvailable = availability.every(e => !!e);
+  const allAvailable = availability.every(e => !!e);
-  let values = [name + ' ' + (allAvailable ? colors.green + revision + colors.reset : revision)];
+  const values = [name + ' ' + (allAvailable ? colors.green + revision + colors.reset : revision)];
   for (let i = 0; i < availability.length; ++i) {
-    let decoration = availability[i] ? '+' : '-';
+    const decoration = availability[i] ? '+' : '-';
-    let color = availability[i] ? colors.green : colors.red;
+    const color = availability[i] ? colors.green : colors.red;
     values.push(color + decoration + colors.reset);
   }
   table.drawRow(values);
@@ -130,7 +130,7 @@ async function checkAndDrawRevisionAvailability(table, name, revision) {
  */
 function loadJSON(url) {
   let resolve;
-  let promise = new Promise(x => resolve = x);
+  const promise = new Promise(x => resolve = x);
   https.get(url, response => {
     if (response.statusCode !== 200) {
       resolve(null);
@@ -141,7 +141,7 @@ function loadJSON(url) {
       body += chunk;
     });
     response.on('end', function(){
-      let json = JSON.parse(body);
+      const json = JSON.parse(body);
       resolve(json);
     });
   }).on('error', function(e){
@@ -164,8 +164,8 @@ function spaceString(size) {
  * @return {string}
  */
 function filterOutColors(text) {
-  for (let colorName in colors) {
+  for (const colorName in colors) {
-    let color = colors[colorName];
+    const color = colors[colorName];
     text = text.replace(color, '');
   }
   return text;
@@ -177,7 +177,7 @@ function filterOutColors(text) {
  * @return {string}
  */
 function padLeft(text, length) {
-  let printableCharacters = filterOutColors(text);
+  const printableCharacters = filterOutColors(text);
   return printableCharacters.length >= length ? text : spaceString(length - text.length) + text;
 }
 
@@ -187,10 +187,10 @@ function padLeft(text, length) {
  * @return {string}
  */
 function padCenter(text, length) {
-  let printableCharacters = filterOutColors(text);
+  const printableCharacters = filterOutColors(text);
   if (printableCharacters.length >= length)
     return text;
-  let left = Math.floor((length - printableCharacters.length) / 2);
+  const left = Math.floor((length - printableCharacters.length) / 2);
-  let right = Math.ceil((length - printableCharacters.length) / 2);
+  const right = Math.ceil((length - printableCharacters.length) / 2);
   return spaceString(left) + text + spaceString(right);
 }

utils/doclint/check_public_api/Documentation.js

@@ -21,7 +21,7 @@ class Documentation {
   constructor(classesArray) {
     this.classesArray = classesArray;
     this.classes = new Map();
-    for (let cls of classesArray)
+    for (const cls of classesArray)
       this.classes.set(cls.name, cls);
   }
 }
@@ -38,7 +38,7 @@ Documentation.Class = class {
     this.properties = new Map();
     this.methods = new Map();
     this.events = new Map();
-    for (let member of membersArray) {
+    for (const member of membersArray) {
       this.members.set(member.name, member);
       if (member.type === 'method')
         this.methods.set(member.name, member);
@@ -65,7 +65,7 @@ Documentation.Member = class {
     this.args = new Map();
     this.hasReturn = hasReturn;
     this.async = async;
-    for (let arg of argsArray)
+    for (const arg of argsArray)
       this.args.set(arg.name, arg);
   }
 

utils/doclint/check_public_api/ESTreeWalker.js

@@ -36,13 +36,13 @@ class ESTreeWalker {
       return;
     }
 
-    let walkOrder = ESTreeWalker._walkOrder[node.type];
+    const walkOrder = ESTreeWalker._walkOrder[node.type];
     if (!walkOrder)
       return;
 
     if (node.type === 'TemplateLiteral') {
-      let templateLiteral = /** @type {!ESTree.TemplateLiteralNode} */ (node);
+      const templateLiteral = /** @type {!ESTree.TemplateLiteralNode} */ (node);
-      let expressionsLength = templateLiteral.expressions.length;
+      const expressionsLength = templateLiteral.expressions.length;
       for (let i = 0; i < expressionsLength; ++i) {
         this._innerWalk(templateLiteral.quasis[i], templateLiteral);
         this._innerWalk(templateLiteral.expressions[i], templateLiteral);
@@ -50,7 +50,7 @@ class ESTreeWalker {
       this._innerWalk(templateLiteral.quasis[expressionsLength], templateLiteral);
     } else {
       for (let i = 0; i < walkOrder.length; ++i) {
-        let entity = node[walkOrder[i]];
+        const entity = node[walkOrder[i]];
         if (Array.isArray(entity))
           this._walkArray(entity, node);
         else

utils/doclint/check_public_api/JSBuilder.js

@@ -27,8 +27,8 @@ class JSOutline {
     this._currentClassMembers = [];
 
     this._text = text;
-    let ast = esprima.parseScript(this._text, {loc: true, range: true});
+    const ast = esprima.parseScript(this._text, {loc: true, range: true});
-    let walker = new ESTreeWalker(node => {
+    const walker = new ESTreeWalker(node => {
       if (node.type === 'ClassDeclaration')
         this._onClassDeclaration(node);
       else if (node.type === 'MethodDefinition')
@@ -49,9 +49,9 @@ class JSOutline {
   _onMethodDefinition(node) {
     console.assert(this._currentClassName !== null);
     console.assert(node.value.type === 'FunctionExpression');
-    let methodName = this._extractText(node.key);
+    const methodName = this._extractText(node.key);
     if (node.kind === 'get') {
-      let property = Documentation.Member.createProperty(methodName);
+      const property = Documentation.Member.createProperty(methodName);
       this._currentClassMembers.push(property);
       return;
     }
@@ -60,7 +60,7 @@ class JSOutline {
     // Extract properties from constructor.
     if (node.kind === 'constructor') {
       // Extract properties from constructor.
-      let walker = new ESTreeWalker(node => {
+      const walker = new ESTreeWalker(node => {
         if (node.type !== 'AssignmentExpression')
           return;
         node = node.left;
@@ -71,7 +71,7 @@ class JSOutline {
       });
       walker.walk(node);
     } else if (!hasReturn) {
-      let walker = new ESTreeWalker(node => {
+      const walker = new ESTreeWalker(node => {
         if (node.type === 'FunctionExpression' || node.type === 'FunctionDeclaration' || node.type === 'ArrowFunctionExpression')
           return ESTreeWalker.SkipSubtree;
         if (node.type === 'ReturnStatement')
@@ -80,7 +80,7 @@ class JSOutline {
       walker.walk(node.value.body);
     }
     const args = [];
-    for (let param of node.value.params) {
+    for (const param of node.value.params) {
       if (param.type === 'AssignmentPattern')
         args.push(new Documentation.Argument(param.left.name));
       else if (param.type === 'RestElement')
@@ -92,7 +92,7 @@ class JSOutline {
       else
         this.errors.push(`JS Parsing issue: unsupported syntax to define parameter in ${this._currentClassName}.${methodName}(): ${this._extractText(param)}`);
     }
-    let method = Documentation.Member.createMethod(methodName, args, hasReturn, node.value.async);
+    const method = Documentation.Member.createMethod(methodName, args, hasReturn, node.value.async);
     this._currentClassMembers.push(method);
     return ESTreeWalker.SkipSubtree;
   }
@@ -108,7 +108,7 @@ class JSOutline {
       events = [];
       this._eventsByClassName.set(className, events);
     }
-    for (let property of node.right.properties) {
+    for (const property of node.right.properties) {
       if (property.type !== 'Property' || property.key.type !== 'Identifier' || property.value.type !== 'Literal')
         continue;
       events.push(Documentation.Member.createEvent(property.value.value));
@@ -118,7 +118,7 @@ class JSOutline {
   _flushClassIfNeeded() {
     if (this._currentClassName === null)
       return;
-    let jsClass = new Documentation.Class(this._currentClassName, this._currentClassMembers);
+    const jsClass = new Documentation.Class(this._currentClassName, this._currentClassMembers);
     this.classes.push(jsClass);
     this._currentClassName = null;
     this._currentClassMembers = [];
@@ -126,8 +126,8 @@ class JSOutline {
 
   _recreateClassesWithEvents() {
     this.classes = this.classes.map(cls => {
-      let events = this._eventsByClassName.get(cls.name) || [];
+      const events = this._eventsByClassName.get(cls.name) || [];
-      let members = cls.membersArray.concat(events);
+      const members = cls.membersArray.concat(events);
       return new Documentation.Class(cls.name, members);
     });
   }
@@ -135,7 +135,7 @@ class JSOutline {
   _extractText(node) {
     if (!node)
       return null;
-    let text = this._text.substring(node.range[0], node.range[1]).trim();
+    const text = this._text.substring(node.range[0], node.range[1]).trim();
     return text;
   }
 }
@@ -145,10 +145,10 @@ class JSOutline {
  * @return {!Promise<{documentation: !Documentation, errors: !Array<string>}>}
  */
 module.exports = async function(sources) {
-  let classes = [];
+  const classes = [];
-  let errors = [];
+  const errors = [];
-  for (let source of sources) {
+  for (const source of sources) {
-    let outline = new JSOutline(source.text());
+    const outline = new JSOutline(source.text());
     classes.push(...outline.classes);
     errors.push(...outline.errors);
   }

utils/doclint/check_public_api/MDBuilder.js

@@ -33,11 +33,11 @@ class MDOutline {
     // Extract headings.
     await page.setContent(html);
     const {classes, errors} = await page.evaluate(() => {
-      let classes = [];
+      const classes = [];
       let currentClass = {};
       let member = {};
-      let errors = [];
+      const errors = [];
-      for (let element of document.body.querySelectorAll('h3, h4, h4 + ul > li')) {
+      for (const element of document.body.querySelectorAll('h3, h4, h4 + ul > li')) {
         if (element.matches('h3')) {
           currentClass = {
             name: element.textContent,
@@ -82,22 +82,22 @@ class MDOutline {
     let currentClassName = null;
     let currentClassMembers = [];
     for (const cls of classes) {
-      let match = cls.name.match(classHeading);
+      const match = cls.name.match(classHeading);
       if (!match)
         continue;
       currentClassName = match[1];
-      for (let member of cls.members) {
+      for (const member of cls.members) {
         if (constructorRegex.test(member.name)) {
-          let match = member.name.match(constructorRegex);
+          const match = member.name.match(constructorRegex);
           handleMethod.call(this, member, match[1], 'constructor', match[2]);
         } else if (methodRegex.test(member.name)) {
-          let match = member.name.match(methodRegex);
+          const match = member.name.match(methodRegex);
           handleMethod.call(this, member, match[1], match[2], match[3]);
         } else if (propertyRegex.test(member.name)) {
-          let match = member.name.match(propertyRegex);
+          const match = member.name.match(propertyRegex);
           handleProperty.call(this, member, match[1], match[2]);
         } else if (eventRegex.test(member.name)) {
-          let match = member.name.match(eventRegex);
+          const match = member.name.match(eventRegex);
           handleEvent.call(this, member, match[1]);
         }
       }
@@ -112,8 +112,8 @@ class MDOutline {
       parameters = parameters.trim().replace(/[\[\]]/g, '');
       if (parameters !== member.args.join(', '))
         this.errors.push(`Heading arguments for "${member.name}" do not match described ones, i.e. "${parameters}" != "${member.args.join(', ')}"`);
-      let args = member.args.map(arg => new Documentation.Argument(arg));
+      const args = member.args.map(arg => new Documentation.Argument(arg));
-      let method = Documentation.Member.createMethod(methodName, args, member.hasReturn, false);
+      const method = Documentation.Member.createMethod(methodName, args, member.hasReturn, false);
       currentClassMembers.push(method);
     }
 
@@ -149,10 +149,10 @@ class MDOutline {
  * @return {!Promise<{documentation: !Documentation, errors: !Array<string>}>}
  */
 module.exports = async function(page, sources) {
-  let classes = [];
+  const classes = [];
-  let errors = [];
+  const errors = [];
-  for (let source of sources) {
+  for (const source of sources) {
-    let outline = await MDOutline.create(page, source.text());
+    const outline = await MDOutline.create(page, source.text());
     classes.push(...outline.classes);
     errors.push(...outline.errors);
   }

utils/doclint/check_public_api/index.js

@@ -58,21 +58,21 @@ const EXCLUDE_METHODS = new Set([
  * @return {!Promise<!Array<!Message>>}
  */
 module.exports = async function lint(page, mdSources, jsSources) {
-  let mdResult = await mdBuilder(page, mdSources);
+  const mdResult = await mdBuilder(page, mdSources);
-  let jsResult = await jsBuilder(jsSources);
+  const jsResult = await jsBuilder(jsSources);
-  let jsDocumentation = filterJSDocumentation(jsResult.documentation);
+  const jsDocumentation = filterJSDocumentation(jsResult.documentation);
-  let mdDocumentation = mdResult.documentation;
+  const mdDocumentation = mdResult.documentation;
 
-  let jsErrors = jsResult.errors;
+  const jsErrors = jsResult.errors;
   jsErrors.push(...checkDuplicates(jsDocumentation));
 
-  let mdErrors = mdResult.errors;
+  const mdErrors = mdResult.errors;
   mdErrors.push(...compareDocumentations(mdDocumentation, jsDocumentation));
   mdErrors.push(...checkDuplicates(mdDocumentation));
   mdErrors.push(...checkSorting(mdDocumentation));
 
   // Push all errors with proper prefixes
-  let errors = jsErrors.map(error => '[JavaScript] ' + error);
+  const errors = jsErrors.map(error => '[JavaScript] ' + error);
   errors.push(...mdErrors.map(error => '[MarkDown] ' + error));
   return errors.map(error => Message.error(error));
 };
@@ -83,8 +83,8 @@ module.exports = async function lint(page, mdSources, jsSources) {
  */
 function checkSorting(doc) {
   const errors = [];
-  for (let cls of doc.classesArray) {
+  for (const cls of doc.classesArray) {
-    let members = cls.membersArray;
+    const members = cls.membersArray;
 
     // Events should go first.
     let eventIndex = 0;
@@ -94,14 +94,14 @@ function checkSorting(doc) {
       errors.push(`Events should go first. Event '${members[eventIndex].name}' in class ${cls.name} breaks order`);
 
     // Constructor should be right after events and before all other members.
-    let constructorIndex = members.findIndex(member => member.type === 'method' && member.name === 'constructor');
+    const constructorIndex = members.findIndex(member => member.type === 'method' && member.name === 'constructor');
     if (constructorIndex > 0 && members[constructorIndex - 1].type !== 'event')
       errors.push(`Constructor of ${cls.name} should go before other methods`);
 
     // Events should be sorted alphabetically.
     for (let i = 0; i < members.length - 1; ++i) {
-      let member1 = cls.membersArray[i];
+      const member1 = cls.membersArray[i];
-      let member2 = cls.membersArray[i + 1];
+      const member2 = cls.membersArray[i + 1];
       if (member1.type !== 'event' || member2.type !== 'event')
         continue;
       if (member1.name > member2.name)
@@ -110,8 +110,8 @@ function checkSorting(doc) {
 
     // All other members should be sorted alphabetically.
     for (let i = 0; i < members.length - 1; ++i) {
-      let member1 = cls.membersArray[i];
+      const member1 = cls.membersArray[i];
-      let member2 = cls.membersArray[i + 1];
+      const member2 = cls.membersArray[i + 1];
       if (member1.type === 'event' || member2.type === 'event')
         continue;
       if (member1.type === 'method' && member1.name === 'constructor')
@@ -136,11 +136,11 @@ function checkSorting(doc) {
  */
 function filterJSDocumentation(jsDocumentation) {
   // Filter classes and methods.
-  let classes = [];
+  const classes = [];
-  for (let cls of jsDocumentation.classesArray) {
+  for (const cls of jsDocumentation.classesArray) {
     if (EXCLUDE_CLASSES.has(cls.name))
       continue;
-    let members = cls.membersArray.filter(member => {
+    const members = cls.membersArray.filter(member => {
       if (member.name.startsWith('_'))
         return false;
       return !EXCLUDE_METHODS.has(`${cls.name}.${member.name}`);
@@ -156,19 +156,19 @@ function filterJSDocumentation(jsDocumentation) {
  */
 function checkDuplicates(doc) {
   const errors = [];
-  let classes = new Set();
+  const classes = new Set();
   // Report duplicates.
-  for (let cls of doc.classesArray) {
+  for (const cls of doc.classesArray) {
     if (classes.has(cls.name))
       errors.push(`Duplicate declaration of class ${cls.name}`);
     classes.add(cls.name);
-    let members = new Set();
+    const members = new Set();
-    for (let member of cls.membersArray) {
+    for (const member of cls.membersArray) {
       if (members.has(member.name))
         errors.push(`Duplicate declaration of method ${cls.name}.${member.name}()`);
       members.add(member.name);
-      let args = new Set();
+      const args = new Set();
-      for (let arg of member.argsArray) {
+      for (const arg of member.argsArray) {
         if (args.has(arg.name))
           errors.push(`Duplicate declaration of argument ${cls.name}.${member.name} "${arg.name}"`);
         args.add(arg.name);
@@ -188,24 +188,24 @@ function compareDocumentations(actual, expected) {
 
   const actualClasses = Array.from(actual.classes.keys()).sort();
   const expectedClasses = Array.from(expected.classes.keys()).sort();
-  let classesDiff = diff(actualClasses, expectedClasses);
+  const classesDiff = diff(actualClasses, expectedClasses);
-  for (let className of classesDiff.extra)
+  for (const className of classesDiff.extra)
     errors.push(`Non-existing class found: ${className}`);
-  for (let className of classesDiff.missing)
+  for (const className of classesDiff.missing)
     errors.push(`Class not found: ${className}`);
 
-  for (let className of classesDiff.equal) {
+  for (const className of classesDiff.equal) {
     const actualClass = actual.classes.get(className);
     const expectedClass = expected.classes.get(className);
     const actualMethods = Array.from(actualClass.methods.keys()).sort();
     const expectedMethods = Array.from(expectedClass.methods.keys()).sort();
     const methodDiff = diff(actualMethods, expectedMethods);
-    for (let methodName of methodDiff.extra)
+    for (const methodName of methodDiff.extra)
       errors.push(`Non-existing method found: ${className}.${methodName}()`);
-    for (let methodName of methodDiff.missing)
+    for (const methodName of methodDiff.missing)
       errors.push(`Method not found: ${className}.${methodName}()`);
 
-    for (let methodName of methodDiff.equal) {
+    for (const methodName of methodDiff.equal) {
       const actualMethod = actualClass.methods.get(methodName);
       const expectedMethod = expectedClass.methods.get(methodName);
       if (actualMethod.hasReturn !== expectedMethod.hasReturn) {
@@ -220,10 +220,10 @@ function compareDocumentations(actual, expected) {
       const expectedArgs = Array.from(expectedMethod.args.keys());
       const argDiff = diff(actualArgs, expectedArgs);
       if (argDiff.extra.length || argDiff.missing.length) {
-        let text = [`Method ${className}.${methodName}() fails to describe its parameters:`];
+        const text = [`Method ${className}.${methodName}() fails to describe its parameters:`];
-        for (let arg of argDiff.missing)
+        for (const arg of argDiff.missing)
           text.push(`- Argument not found: ${arg}`);
-        for (let arg of argDiff.extra)
+        for (const arg of argDiff.extra)
           text.push(`- Non-existing argument found: ${arg}`);
         errors.push(text.join('\n'));
       }
@@ -231,17 +231,17 @@ function compareDocumentations(actual, expected) {
     const actualProperties = Array.from(actualClass.properties.keys()).sort();
     const expectedProperties = Array.from(expectedClass.properties.keys()).sort();
     const propertyDiff = diff(actualProperties, expectedProperties);
-    for (let propertyName of propertyDiff.extra)
+    for (const propertyName of propertyDiff.extra)
       errors.push(`Non-existing property found: ${className}.${propertyName}`);
-    for (let propertyName of propertyDiff.missing)
+    for (const propertyName of propertyDiff.missing)
       errors.push(`Property not found: ${className}.${propertyName}`);
 
     const actualEvents = Array.from(actualClass.events.keys()).sort();
     const expectedEvents = Array.from(expectedClass.events.keys()).sort();
     const eventsDiff = diff(actualEvents, expectedEvents);
-    for (let eventName of eventsDiff.extra)
+    for (const eventName of eventsDiff.extra)
       errors.push(`Non-existing event found in class ${className}: '${eventName}'`);
-    for (let eventName of eventsDiff.missing)
+    for (const eventName of eventsDiff.missing)
       errors.push(`Event not found in class ${className}: '${eventName}'`);
   }
   return errors;
@@ -261,8 +261,8 @@ function diff(actual, expected) {
     return {extra: [], missing: expected.slice(), equal: []};
   if (M === 0)
     return {extra: actual.slice(), missing: [], equal: []};
-  let d = new Array(N);
+  const d = new Array(N);
-  let bt = new Array(N);
+  const bt = new Array(N);
   for (let i = 0; i < N; ++i) {
     d[i] = new Array(M);
     bt[i] = new Array(M);
@@ -276,7 +276,7 @@ function diff(actual, expected) {
         d[i][j] = left;
         bt[i][j] = 'missing';
       }
-      let diag = val(i - 1, j - 1);
+      const diag = val(i - 1, j - 1);
       if (actual[i] === expected[j] && d[i][j] < diag + 1) {
         d[i][j] = diag + 1;
         bt[i][j] = 'eq';
@@ -286,9 +286,9 @@ function diff(actual, expected) {
   // Backtrack results.
   let i = N - 1;
   let j = M - 1;
-  let missing = [];
+  const missing = [];
-  let extra = [];
+  const extra = [];
-  let equal = [];
+  const equal = [];
   while (i >= 0 && j >= 0) {
     switch (bt[i][j]) {
       case 'extra':

utils/doclint/preprocessor/index.js

@@ -19,9 +19,9 @@ const Message = require('../Message');
 const PUPPETEER_VERSION = require('../../../package.json').version;
 
 module.exports = function(sources) {
-  let messages = [];
+  const messages = [];
   let commands = [];
-  for (let source of sources) {
+  for (const source of sources) {
     const text = source.text();
     const commandStartRegex = /<!--\s*gen:([a-z]+)(?:\s*\(\s*([^)]*)\s*\))?\s*-->/ig;
     const commandEndRegex = /<!--\s*gen:stop\s*-->/ig;
@@ -45,10 +45,10 @@ module.exports = function(sources) {
 
   commands = validateCommands(commands, messages);
 
-  let changedSources = new Set();
+  const changedSources = new Set();
   // Iterate commands in reverse order so that edits don't conflict.
   commands.sort((a, b) => b.from - a.from);
-  for (let command of commands) {
+  for (const command of commands) {
     let newText = command.source.text();
     if (command.name === 'version')
       newText = replaceInText(newText, command.from, command.to, PUPPETEER_VERSION);
@@ -67,7 +67,7 @@ module.exports = function(sources) {
  */
 function validateCommands(commands, outMessages) {
   // Filter sane commands
-  let goodCommands = commands.filter(command => {
+  const goodCommands = commands.filter(command => {
     if (command.name === 'version')
       return check(command, !command.arg, `"gen:version" should not have argument`);
     check(command, false, `Unknown command: "gen:${command.name}"`);

utils/doclint/preprocessor/test.js

@@ -21,8 +21,8 @@ const VERSION = require('../../../package.json').version;
 
 describe('preprocessor', function() {
   it('should throw for unknown command', function() {
-    let source = factory.createForTest('doc.md', getCommand('unknownCommand()'));
+    const source = factory.createForTest('doc.md', getCommand('unknownCommand()'));
-    let messages = preprocessor([source]);
+    const messages = preprocessor([source]);
     expect(source.hasUpdatedText()).toBe(false);
     expect(messages.length).toBe(1);
     expect(messages[0].type).toBe('error');
@@ -30,22 +30,22 @@ describe('preprocessor', function() {
   });
   describe('gen:version', function() {
     it('should work', function() {
-      let source = factory.createForTest('doc.md', `Puppeteer v${getCommand('version')}`);
+      const source = factory.createForTest('doc.md', `Puppeteer v${getCommand('version')}`);
-      let messages = preprocessor([source]);
+      const messages = preprocessor([source]);
       expect(messages.length).toBe(1);
       expect(messages[0].type).toBe('warning');
       expect(messages[0].text).toContain('doc.md');
       expect(source.text()).toBe(`Puppeteer v${getCommand('version', VERSION)}`);
     });
     it('should tolerate different writing', function() {
-      let source = factory.createForTest('doc.md', `Puppeteer v<!--   gEn:version (  ) -->WHAT
+      const source = factory.createForTest('doc.md', `Puppeteer v<!--   gEn:version (  ) -->WHAT
 <!--     GEN:stop   -->`);
       preprocessor([source]);
       expect(source.text()).toBe(`Puppeteer v<!--   gEn:version (  ) -->${VERSION}<!--     GEN:stop   -->`);
     });
     it('should not tolerate missing gen:stop', function() {
-      let source = factory.createForTest('doc.md', `<!--GEN:version-->`);
+      const source = factory.createForTest('doc.md', `<!--GEN:version-->`);
-      let messages = preprocessor([source]);
+      const messages = preprocessor([source]);
       expect(source.hasUpdatedText()).toBe(false);
       expect(messages.length).toBe(1);
       expect(messages[0].type).toBe('error');

utils/doclint/toc.js

@@ -23,7 +23,7 @@ const Message = require('./Message');
  */
 module.exports = function(sources) {
   const warnings = [];
-  for (let source of sources) {
+  for (const source of sources) {
     const newText = markdownToc.insert(source.text());
     if (source.setText(newText))
       warnings.push('Regenerated table-of-contexts: ' + source.projectPath());

utils/fetch_devices.js

@@ -52,7 +52,7 @@ Fetch Chrome DevTools front-end emulation devices from given URL, convert them t
 devices and save to the <outputPath>.
 `;
 
-let argv = require('minimist')(process.argv.slice(2), {
+const argv = require('minimist')(process.argv.slice(2), {
   alias: { u: 'url', h: 'help' },
 });
 
@@ -61,8 +61,8 @@ if (argv.help) {
   return;
 }
 
-let url = argv.url || DEVICES_URL;
+const url = argv.url || DEVICES_URL;
-let outputPath = argv._[0];
+const outputPath = argv._[0];
 if (!outputPath) {
   console.log('ERROR: output file name is missing. Use --help for help.');
   return;
@@ -72,7 +72,7 @@ main(url);
 
 async function main(url) {
   console.log('GET ' + url);
-  let text = await httpGET(url);
+  const text = await httpGET(url);
   let json = null;
   try {
     json = JSON.parse(text);
@@ -80,11 +80,11 @@ async function main(url) {
     console.error(`FAILED: error parsing response - ${e.message}`);
     return;
   }
-  let devicePayloads = json.extensions.filter(extension => extension.type === 'emulated-device').map(extension => extension.device);
+  const devicePayloads = json.extensions.filter(extension => extension.type === 'emulated-device').map(extension => extension.device);
   let devices = [];
-  for (let payload of devicePayloads) {
+  for (const payload of devicePayloads) {
-    let device = createDevice(payload, false);
+    const device = createDevice(payload, false);
-    let landscape = createDevice(payload, true);
+    const landscape = createDevice(payload, true);
     devices.push(device);
     if (landscape.viewport.width !== device.viewport.width || landscape.viewport.height !== device.viewport.height)
       devices.push(landscape);
@@ -92,10 +92,10 @@ async function main(url) {
   devices = devices.filter(device => device.viewport.isMobile);
   devices.sort((a, b) => a.name.localeCompare(b.name));
   // Use single-quotes instead of double-quotes to conform with codestyle.
-  let serialized = JSON.stringify(devices, null, 2)
+  const serialized = JSON.stringify(devices, null, 2)
       .replace(/'/g, `\\'`)
       .replace(/"/g, `'`);
-  let result = util.format(template, serialized);
+  const result = util.format(template, serialized);
   fs.writeFileSync(outputPath, result, 'utf8');
 }