diff --git a/lib/Browser.js b/lib/Browser.js
index 1c516b81..98f4505d 100644
--- a/lib/Browser.js
+++ b/lib/Browser.js
@@ -20,9 +20,9 @@ const EventEmitter = require('events');
 
 class Browser extends EventEmitter {
   /**
-   * @param {!Connection} connection
+   * @param {!Puppeteer.Connection} connection
    * @param {!Object=} options
-   * @param {function():Promise=} closeCallback
+   * @param {(function():Promise)=} closeCallback
    */
   constructor(connection, options = {}, closeCallback) {
     super();
@@ -63,7 +63,6 @@ class Browser extends EventEmitter {
   }
 }
 
-module.exports = Browser;
 helper.tracePublicAPI(Browser);
 
 class TaskQueue {
@@ -81,3 +80,4 @@ class TaskQueue {
     return result;
   }
 }
+module.exports = { Browser, TaskQueue };
diff --git a/lib/Connection.js b/lib/Connection.js
index c99584c3..fa4501b0 100644
--- a/lib/Connection.js
+++ b/lib/Connection.js
@@ -173,7 +173,7 @@ class Session extends EventEmitter {
       if (!this._callbacks.has(id))
         return;
       const callback = this._callbacks.get(id);
-      this._callbacks.delete(object.id);
+      this._callbacks.delete(id);
       callback.reject(e);
     });
     return new Promise((resolve, reject) => {
@@ -212,4 +212,4 @@ class Session extends EventEmitter {
   }
 }
 
-module.exports = Connection;
+module.exports = {Connection, Session};
diff --git a/lib/Dialog.js b/lib/Dialog.js
index ebac447c..55ff5e11 100644
--- a/lib/Dialog.js
+++ b/lib/Dialog.js
@@ -18,8 +18,8 @@ const {helper} = require('./helper');
 
 class Dialog {
   /**
-   * @param {!Session} client
-   * @param {!Dialog.Type} type
+   * @param {!Puppeteer.Session} client
+   * @param {string} type
    * @param {string} message
    * @param {(string|undefined)} defaultValue
    */
diff --git a/lib/ElementHandle.js b/lib/ElementHandle.js
index d04ebf24..dace1b04 100644
--- a/lib/ElementHandle.js
+++ b/lib/ElementHandle.js
@@ -19,10 +19,10 @@ const {helper} = require('./helper');
 
 class ElementHandle extends JSHandle {
   /**
-   * @param {!ExecutionContext} context
-   * @param {!Session} client
+   * @param {!Puppeteer.ExecutionContext} context
+   * @param {!Puppeteer.Session} client
    * @param {!Object} remoteObject
-   * @param {!Page} page
+   * @param {!Puppeteer.Page} page
    */
   constructor(context, client, remoteObject, page) {
     super(context, client, remoteObject);
@@ -47,7 +47,7 @@ class ElementHandle extends JSHandle {
     const error = await this.executionContext().evaluate(element => {
       if (!element.ownerDocument.contains(element))
         return 'Node is detached from document';
-      if (element.nodeType !== HTMLElement.ELEMENT_NODE)
+      if (element.nodeType !== Node.ELEMENT_NODE)
         return 'Node is not of type HTMLElement';
       element.scrollIntoViewIfNeeded();
     }, this);
diff --git a/lib/EmulationManager.js b/lib/EmulationManager.js
index 23b1e80a..a1c2c598 100644
--- a/lib/EmulationManager.js
+++ b/lib/EmulationManager.js
@@ -16,7 +16,7 @@
 
 class EmulationManager {
   /**
-   * @param {!Session} client
+   * @param {!Puppeteer.Session} client
    */
   constructor(client) {
     this._client = client;
@@ -25,7 +25,7 @@ class EmulationManager {
   }
 
   /**
-   * @param {!Page.Viewport} viewport
+   * @param {!EmulationManager.Viewport} viewport
    * @return {Promise<boolean>}
    */
   async emulateViewport(client, viewport) {
@@ -61,6 +61,7 @@ class EmulationManager {
 
     function injectedTouchEventsFunction() {
       const touchEvents = ['ontouchstart', 'ontouchend', 'ontouchmove', 'ontouchcancel'];
+      // @ts-ignore
       const recepients = [window.__proto__, document.__proto__];
       for (let i = 0; i < touchEvents.length; ++i) {
         for (let j = 0; j < recepients.length; ++j) {
@@ -75,4 +76,14 @@ class EmulationManager {
   }
 }
 
+/**
+ * @typedef {Object} EmulationManager.Viewport
+ * @property {number} width
+ * @property {number} height
+ * @property {number=} deviceScaleFactor
+ * @property {boolean=} isMobile
+ * @property {boolean=} isLandscape
+ * @property {boolean=} hasTouch
+ */
+
 module.exports = EmulationManager;
diff --git a/lib/ExecutionContext.js b/lib/ExecutionContext.js
index 7f10eb0b..7753d153 100644
--- a/lib/ExecutionContext.js
+++ b/lib/ExecutionContext.js
@@ -18,7 +18,7 @@ const {helper} = require('./helper');
 
 class ExecutionContext {
   /**
-   * @param {!Session} client
+   * @param {!Puppeteer.Session} client
    * @param {string} contextId
    * @param {function(*):!JSHandle} objectHandleFactory
    */
@@ -100,7 +100,7 @@ class ExecutionContext {
 class JSHandle {
   /**
    * @param {!ExecutionContext} context
-   * @param {!Session} client
+   * @param {!Puppeteer.Session} client
    * @param {!Object} remoteObject
    */
   constructor(context, client, remoteObject) {
@@ -134,7 +134,7 @@ class JSHandle {
   }
 
   /**
-   * @return {!Property<Map<string, !ObjectHandle>>}
+   * @return {!Promise<Map<string, !JSHandle>>}
    */
   async getProperties() {
     const response = await this._client.send('Runtime.getProperties', {
@@ -162,7 +162,7 @@ class JSHandle {
   }
 
   /**
-   * @return {?ElementHandle}
+   * @return {?Puppeteer.ElementHandle}
    */
   asElement() {
     return null;
diff --git a/lib/FrameManager.js b/lib/FrameManager.js
index 8e6cf6c8..0b03e54c 100644
--- a/lib/FrameManager.js
+++ b/lib/FrameManager.js
@@ -22,8 +22,8 @@ const ElementHandle = require('./ElementHandle');
 
 class FrameManager extends EventEmitter {
   /**
-   * @param {!Session} client
-   * @param {!Page} page
+   * @param {!Puppeteer.Session} client
+   * @param {!Puppeteer.Page} page
    */
   constructor(client, page) {
     super();
@@ -87,7 +87,7 @@ class FrameManager extends EventEmitter {
     if (isMainFrame) {
       if (frame) {
         // Update frame id to retain frame identity on cross-process navigation.
-        this._frames.delete(frame._id, frame);
+        this._frames.delete(frame._id);
         frame._id = framePayload.id;
       } else {
         // Initial main frame navigation.
@@ -154,7 +154,6 @@ class FrameManager extends EventEmitter {
   }
 
   /**
-   * @param {!Frame} frame
    * @return {boolean}
    */
   isMainFrameLoadingFailed() {
@@ -174,7 +173,7 @@ FrameManager.Events = {
  */
 class Frame {
   /**
-   * @param {!Session} client
+   * @param {!Puppeteer.Session} client
    * @param {?Frame} parentFrame
    * @param {string} frameId
    */
@@ -202,9 +201,9 @@ class Frame {
   }
 
   /**
-   * @param {function()|string} pageFunction
+   * @param {Function|string} pageFunction
    * @param {!Array<*>} args
-   * @return {!Promise<(!Object|undefined)>}
+   * @return {!Promise<*>}
    */
   async evaluate(pageFunction, ...args) {
     return this._context.evaluate(pageFunction, ...args);
@@ -225,7 +224,7 @@ class Frame {
 
   /**
    * @param {string} selector
-   * @param {function()|string} pageFunction
+   * @param {Function|string} pageFunction
    * @param {!Array<*>} args
    * @return {!Promise<(!Object|undefined)>}
    */
@@ -344,14 +343,14 @@ class Frame {
   }
 
   /**
-   * @param {(string|number|function())} selectorOrTimeout
+   * @param {(string|number|Function)} selectorOrFunctionOrTimeout
    * @param {!Object=} options
    * @param {!Array<*>} args
    * @return {!Promise}
    */
   waitFor(selectorOrFunctionOrTimeout, options = {}, ...args) {
     if (helper.isString(selectorOrFunctionOrTimeout))
-      return this.waitForSelector(selectorOrFunctionOrTimeout, options);
+      return this.waitForSelector(/** @type {string} */(selectorOrFunctionOrTimeout), options);
     if (helper.isNumber(selectorOrFunctionOrTimeout))
       return new Promise(fulfill => setTimeout(fulfill, selectorOrFunctionOrTimeout));
     if (typeof selectorOrFunctionOrTimeout === 'function')
@@ -387,7 +386,7 @@ class Frame {
   }
 
   /**
-   * @param {function()} pageFunction
+   * @param {Function} pageFunction
    * @param {!Object=} options
    * @return {!Promise}
    */
@@ -429,7 +428,7 @@ class WaitTask {
   /**
    * @param {!Frame} frame
    * @param {string} predicateBody
-   * @param {string} polling
+   * @param {string|number} polling
    * @param {number} timeout
    */
   constructor(frame, predicateBody, polling, timeout) {
@@ -524,7 +523,7 @@ async function waitForPredicatePageFunction(predicateBody, polling, timeout) {
   return !timedOut;
 
   /**
-   * @return {!Promise<!Element>}
+   * @return {!Promise}
    */
   function pollMutation() {
     if (predicate())
@@ -582,4 +581,4 @@ async function waitForPredicatePageFunction(predicateBody, polling, timeout) {
   }
 }
 
-module.exports = FrameManager;
+module.exports = {FrameManager, Frame};
diff --git a/lib/Input.js b/lib/Input.js
index a6968167..b14992bf 100644
--- a/lib/Input.js
+++ b/lib/Input.js
@@ -18,7 +18,7 @@ const {helper} = require('./helper');
 
 class Keyboard {
   /**
-   * @param {!Session} client
+   * @param {!Puppeteer.Session} client
    */
   constructor(client) {
     this._client = client;
@@ -28,10 +28,10 @@ class Keyboard {
 
   /**
    * @param {string} key
-   * @param {{text: (string|undefined)}} options
+   * @param {{text: string}=} options
    */
-  async down(key, options = {}) {
-    const text = options.text;
+  async down(key, options = {text: ''}) {
+    const {text} = options;
     const autoRepeat = this._pressedKeys.has(key);
     this._pressedKeys.add(key);
     this._modifiers |= this._modifierBit(key);
@@ -118,7 +118,7 @@ class Keyboard {
 
 class Mouse {
   /**
-   * @param {!Session} client
+   * @param {Puppeteer.Session} client
    * @param {!Keyboard} keyboard
    */
   constructor(client, keyboard) {
@@ -197,7 +197,7 @@ class Mouse {
 
 class Touchscreen {
   /**
-   * @param {Session} client
+   * @param {Puppeteer.Session} client
    * @param {Keyboard} keyboard
    */
   constructor(client, keyboard) {
diff --git a/lib/Launcher.js b/lib/Launcher.js
index a6e8cd9d..152afdf8 100644
--- a/lib/Launcher.js
+++ b/lib/Launcher.js
@@ -18,11 +18,12 @@ const path = require('path');
 const removeSync = require('rimraf').sync;
 const childProcess = require('child_process');
 const Downloader = require('../utils/ChromiumDownloader');
-const Connection = require('./Connection');
-const Browser = require('./Browser');
+const {Connection} = require('./Connection');
+const {Browser} = require('./Browser');
 const readline = require('readline');
 const fs = require('fs');
 const {helper} = require('./helper');
+// @ts-ignore
 const ChromiumRevision = require('../package.json').puppeteer.chromium_revision;
 
 const CHROME_PROFILE_PATH = path.join(os.tmpdir(), 'puppeteer_dev_profile-');
@@ -178,7 +179,7 @@ class Launcher {
 }
 
 /**
- * @param {!ChildProcess} chromeProcess
+ * @param {!Puppeteer.ChildProcess} chromeProcess
  * @param {number} timeout
  * @return {!Promise<string>}
  */
diff --git a/lib/Multimap.js b/lib/Multimap.js
index 213a782c..6e9c0769 100644
--- a/lib/Multimap.js
+++ b/lib/Multimap.js
@@ -14,19 +14,11 @@
  * limitations under the License.
  */
 
-/**
- * @template K, V
- */
 class Multimap {
   constructor() {
-    /** @type {!Map<K, !Set<!V>>} */
     this._map = new Map();
   }
 
-  /**
-   * @param {K} key
-   * @param {V} value
-   */
   set(key, value) {
     let set = this._map.get(key);
     if (!set) {
@@ -36,10 +28,6 @@ class Multimap {
     set.add(value);
   }
 
-  /**
-   * @param {K} key
-   * @return {!Set<!V>}
-   */
   get(key) {
     let result = this._map.get(key);
     if (!result)
@@ -47,19 +35,10 @@ class Multimap {
     return result;
   }
 
-  /**
-   * @param {K} key
-   * @return {boolean}
-   */
   has(key) {
     return this._map.has(key);
   }
 
-  /**
-   * @param {K} key
-   * @param {V} value
-   * @return {boolean}
-   */
   hasValue(key, value) {
     const set = this._map.get(key);
     if (!set)
@@ -74,11 +53,6 @@ class Multimap {
     return this._map.size;
   }
 
-  /**
-   * @param {K} key
-   * @param {V} value
-   * @return {boolean}
-   */
   delete(key, value) {
     const values = this.get(key);
     const result = values.delete(value);
@@ -87,17 +61,10 @@ class Multimap {
     return result;
   }
 
-  /**
-   * @param {K} key
-   */
   deleteAll(key) {
     this._map.delete(key);
   }
 
-  /**
-   * @param {K} key
-   * @return {?V} value
-   */
   firstValue(key) {
     const set = this._map.get(key);
     if (!set)
@@ -105,16 +72,10 @@ class Multimap {
     return set.values().next().value;
   }
 
-  /**
-   * @return {K}
-   */
   firstKey() {
     return this._map.keys().next().value;
   }
 
-  /**
-   * @return {!Array<!V>}
-   */
   valuesArray() {
     const result = [];
     for (const key of this._map.keys())
@@ -122,9 +83,6 @@ class Multimap {
     return result;
   }
 
-  /**
-   * @return {!Array<!K>}
-   */
   keysArray() {
     return Array.from(this._map.keys());
   }
diff --git a/lib/NavigatorWatcher.js b/lib/NavigatorWatcher.js
index 808e9bce..5f8b6580 100644
--- a/lib/NavigatorWatcher.js
+++ b/lib/NavigatorWatcher.js
@@ -18,7 +18,7 @@ const {helper} = require('./helper');
 
 class NavigatorWatcher {
   /**
-   * @param {!Session} client
+   * @param {!Puppeteer.Session} client
    * @param {boolean} ignoreHTTPSErrors
    * @param {!Object=} options
    */
diff --git a/lib/NetworkManager.js b/lib/NetworkManager.js
index a37fe777..1b790c86 100644
--- a/lib/NetworkManager.js
+++ b/lib/NetworkManager.js
@@ -20,7 +20,7 @@ const url = require('url');
 
 class NetworkManager extends EventEmitter {
   /**
-   * @param {!Session} client
+   * @param {Puppeteer.Session} client
    */
   constructor(client) {
     super();
@@ -38,9 +38,9 @@ class NetworkManager extends EventEmitter {
     this._attemptedAuthentications = new Set();
     this._userRequestInterceptionEnabled = false;
     this._protocolRequestInterceptionEnabled = false;
-    /** @type {!Multimap<string, string>} */
+    /** @type {!Multimap} */
     this._requestHashToRequestIds = new Multimap();
-    /** @type {!Multimap<string, !Object>} */
+    /** @type {!Multimap} */
     this._requestHashToInterceptions = new Multimap();
 
     this._client.on('Network.requestWillBeSent', this._onRequestWillBeSent.bind(this));
@@ -116,7 +116,7 @@ class NetworkManager extends EventEmitter {
         response = 'ProvideCredentials';
         this._attemptedAuthentications.add(event.interceptionId);
       }
-      const {username, password} = this._credentials || {};
+      const {username, password} = this._credentials || {username: undefined, password: undefined};
       this._client.send('Network.continueInterceptedRequest', {
         interceptionId: event.interceptionId,
         authChallengeResponse: { response, username, password }
@@ -192,7 +192,6 @@ class NetworkManager extends EventEmitter {
 
   /**
    * @param {string} requestHash
-   * @param {!{requestEvent: ?Object, interceptionEvent: ?Object}} interception
    */
   _maybeResolveInterception(requestHash) {
     const requestId = this._requestHashToRequestIds.firstValue(requestHash);
@@ -252,10 +251,10 @@ class NetworkManager extends EventEmitter {
 
 class Request {
   /**
-   * @param {!Connection} client
+   * @param {!Puppeteer.Session} client
    * @param {string} requestId
    * @param {string} interceptionId
-   * @param {string} allowInterception
+   * @param {boolean} allowInterception
    * @param {string} url
    * @param {string} resourceType
    * @param {!Object} payload
@@ -331,9 +330,9 @@ helper.tracePublicAPI(Request);
 
 class Response {
   /**
-   * @param {!Session} client
+   * @param {!Puppeteer.Session} client
    * @param {!Request} request
-   * @param {integer} status
+   * @param {number} status
    * @param {!Object} headers
    */
   constructor(client, request, status, headers) {
@@ -381,7 +380,7 @@ class Response {
   }
 
   /**
-   * @return {!Response}
+   * @return {!Request}
    */
   request() {
     return this._request;
diff --git a/lib/Page.js b/lib/Page.js
index f369dc3d..6df0fd1f 100644
--- a/lib/Page.js
+++ b/lib/Page.js
@@ -21,18 +21,17 @@ const NetworkManager = require('./NetworkManager');
 const NavigatorWatcher = require('./NavigatorWatcher');
 const Dialog = require('./Dialog');
 const EmulationManager = require('./EmulationManager');
-const FrameManager = require('./FrameManager');
+const {FrameManager} = require('./FrameManager');
 const {Keyboard, Mouse, Touchscreen} = require('./Input');
 const Tracing = require('./Tracing');
 const {helper, debugError} = require('./helper');
 
 class Page extends EventEmitter {
   /**
-   * @param {!Session} client
-   * @param {string} sessionId
+   * @param {!Puppeteer.Session} client
    * @param {boolean} ignoreHTTPSErrors
    * @param {boolean} appMode
-   * @param {!TaskQueue} screenshotTaskQueue
+   * @param {!Puppeteer.TaskQueue} screenshotTaskQueue
    * @return {!Promise<!Page>}
    */
   static async create(client, ignoreHTTPSErrors, appMode, screenshotTaskQueue) {
@@ -53,9 +52,9 @@ class Page extends EventEmitter {
   }
 
   /**
-   * @param {!Session} client
+   * @param {!Puppeteer.Session} client
    * @param {boolean} ignoreHTTPSErrors
-   * @param {!TaskQueue} screenshotTaskQueue
+   * @param {!Puppeteer.TaskQueue} screenshotTaskQueue
    */
   constructor(client, ignoreHTTPSErrors, screenshotTaskQueue) {
     super();
@@ -67,7 +66,7 @@ class Page extends EventEmitter {
     this._networkManager = new NetworkManager(client);
     this._emulationManager = new EmulationManager(client);
     this._tracing = new Tracing(client);
-    /** @type {!Map<string, function>} */
+    /** @type {!Map<string, Function>} */
     this._pageBindings = new Map();
     this._ignoreHTTPSErrors = ignoreHTTPSErrors;
 
@@ -95,7 +94,7 @@ class Page extends EventEmitter {
   }
 
   /**
-   * @return {!Frame}
+   * @return {!Puppeteer.Frame}
    */
   mainFrame() {
     return this._frameManager.mainFrame();
@@ -133,7 +132,7 @@ class Page extends EventEmitter {
   }
 
   /**
-   * @return {!Array<!Frame>}
+   * @return {!Array<Puppeteer.Frame>}
    */
   frames() {
     return this._frameManager.frames();
@@ -160,17 +159,16 @@ class Page extends EventEmitter {
 
   /**
    * @param {string} selector
-   * @return {!Promise<?ElementHandle>}
+   * @return {!Promise<?Puppeteer.ElementHandle>}
    */
   async $(selector) {
     return this.mainFrame().$(selector);
   }
 
   /**
-   * @param {string} selector
    * @param {function()|string} pageFunction
    * @param {!Array<*>} args
-   * @return {!Promise<!JSHandle>}
+   * @return {!Promise<!Puppeteer.JSHandle>}
    */
   async evaluateHandle(pageFunction, ...args) {
     return this.mainFrame().executionContext().evaluateHandle(pageFunction, ...args);
@@ -188,7 +186,7 @@ class Page extends EventEmitter {
 
   /**
    * @param {string} selector
-   * @return {!Promise<!Array<!ElementHandle>>}
+   * @return {!Promise<!Array<!Puppeteer.ElementHandle>>}
    */
   async $$(selector) {
     return this.mainFrame().$$(selector);
@@ -385,7 +383,7 @@ class Page extends EventEmitter {
   }
 
   /**
-   * @param {string} html
+   * @param {string} url
    * @param {!Object=} options
    * @return {!Promise<?Response>}
    */
@@ -518,7 +516,7 @@ class Page extends EventEmitter {
   /**
    * @param {function()} pageFunction
    * @param {!Array<*>} args
-   * @return {!Promise<(!Object|undefined)>}
+   * @return {!Promise<*>}
    */
   async evaluate(pageFunction, ...args) {
     return this._frameManager.mainFrame().evaluate(pageFunction, ...args);
@@ -749,7 +747,7 @@ class Page extends EventEmitter {
   }
 
   /**
-   * @param {(string|number|function())} selectorOrTimeout
+   * @param {(string|number|Function)} selectorOrFunctionOrTimeout
    * @param {!Object=} options
    * @param {!Array<*>} args
    * @return {!Promise}
@@ -811,7 +809,7 @@ function convertPrintParameterToInches(parameter) {
     // Treat numbers as pixel values to be aligned with phantom's paperSize.
     pixels = /** @type {number} */ (parameter);
   } else if (helper.isString(parameter)) {
-    const text = parameter;
+    const text = /** @type {string} */ (parameter);
     let unit = text.substring(text.length - 2).toLowerCase();
     let valueText = '';
     if (unitToPixels.hasOwnProperty(unit)) {
@@ -848,8 +846,15 @@ Page.Events = {
   Load: 'load',
 };
 
-/** @typedef {{width: number, height: number, deviceScaleFactor: number|undefined, isMobile: boolean|undefined, isLandscape: boolean, hasTouch: boolean|undefined}} */
-Page.Viewport;
+/**
+ * @typedef {Object} Page.Viewport
+ * @property {number} width
+ * @property {number} height
+ * @property {number=} deviceScaleFactor
+ * @property {boolean=} isMobile
+ * @property {boolean=} isLandscape
+ * @property {boolean=} hasTouch
+ */
 
 /**
  * @typedef {Object} Network.Cookie
diff --git a/lib/Puppeteer.js b/lib/Puppeteer.js
index 2caa58be..0a44db1d 100644
--- a/lib/Puppeteer.js
+++ b/lib/Puppeteer.js
@@ -19,15 +19,15 @@ const Launcher = require('./Launcher');
 class Puppeteer {
   /**
    * @param {!Object=} options
-   * @return {!Promise<!Browser>}
+   * @return {!Promise<!Puppeteer.Browser>}
    */
   static launch(options) {
     return Launcher.launch(options);
   }
 
   /**
-   * @param {string} options
-   * @return {!Promise<!Browser>}
+   * @param {{browserWSEndpoint: string, ignoreHTTPSErrors: boolean}} options
+   * @return {!Promise<!Puppeteer.Browser>}
    */
   static connect(options) {
     return Launcher.connect(options);
diff --git a/lib/Tracing.js b/lib/Tracing.js
index 583fe48b..1732164a 100644
--- a/lib/Tracing.js
+++ b/lib/Tracing.js
@@ -18,7 +18,7 @@ const {helper} = require('./helper');
 
 class Tracing {
   /**
-   * @param {!Session} client
+   * @param {!Puppeteer.Session} client
    */
   constructor(client) {
     this._client = client;
diff --git a/lib/externs.d.ts b/lib/externs.d.ts
new file mode 100644
index 00000000..dcadfdb2
--- /dev/null
+++ b/lib/externs.d.ts
@@ -0,0 +1,28 @@
+import { Connection as RealConnection, Session as RealSession } from './Connection.js';
+import {Browser as RealBrowser, TaskQueue as RealTaskQueue} from './Browser.js';
+import * as RealPage from './Page.js';
+import {Mouse as RealMouse, Keyboard as RealKeyboard, Touchscreen as RealTouchscreen}  from './Input.js';
+import {Frame as RealFrame, FrameManager as RealFrameManager}  from './FrameManager.js';
+import {JSHandle as RealJSHandle, ExecutionContext as RealExecutionContext}  from './ExecutionContext.js';
+import * as RealElementHandle  from './ElementHandle.js';
+import * as RealNetworkManager from './NetworkManager.js';
+import * as child_process from 'child_process';
+export as namespace Puppeteer;
+
+export class Connection extends RealConnection {}
+export class Session extends RealSession {}
+export class Mouse extends RealMouse {}
+export class Keyboard extends RealKeyboard {}
+export class Touchscreen extends RealTouchscreen {}
+export class TaskQueue extends RealTaskQueue {}
+export class Browser extends RealBrowser {}
+export class Frame extends RealFrame {}
+export class FrameManager extends RealFrameManager {}
+export class NetworkManager extends RealNetworkManager {}
+export class ElementHandle extends RealElementHandle {}
+export class JSHandle extends RealJSHandle {}
+export class ExecutionContext extends RealExecutionContext {}
+export class Page extends RealPage {}
+
+
+export interface ChildProcess extends child_process.ChildProcess {}
diff --git a/lib/helper.js b/lib/helper.js
index 4245fad4..ad14533c 100644
--- a/lib/helper.js
+++ b/lib/helper.js
@@ -19,14 +19,14 @@ const debugError = require('debug')(`puppeteer:error`);
 let apiCoverage = null;
 class Helper {
   /**
-   * @param {function()|string} fun
+   * @param {Function|string} fun
    * @param {!Array<*>} args
    * @return {string}
    */
   static evaluationString(fun, ...args) {
     if (Helper.isString(fun)) {
       console.assert(args.length === 0, 'Cannot evaluate a string with arguments');
-      return fun;
+      return /** @type {string} */ (fun);
     }
     return `(${fun})(${args.map(serializeArgument).join(',')})`;
 
@@ -60,9 +60,8 @@ class Helper {
   }
 
   /**
-   * @param {!Session} client
    * @param {!Object} remoteObject
-   * @return {!Promise<!Object>}
+   * @return {*}
    */
   static valueFromRemoteObject(remoteObject) {
     console.assert(!remoteObject.objectId, 'Cannot extract value when objectId is given');
@@ -84,7 +83,7 @@ class Helper {
   }
 
   /**
-   * @param {!Session} client
+   * @param {!Puppeteer.Session} client
    * @param {!Object} remoteObject
    */
   static async releaseObject(client, remoteObject) {
@@ -165,10 +164,10 @@ class Helper {
   }
 
   /**
-   * @param {!EventEmitter} emitter
+   * @param {!NodeJS.EventEmitter} emitter
    * @param {string} eventName
    * @param {function(?)} handler
-   * @return {{emitter: !EventEmitter, eventName: string, handler: function(?)}}
+   * @return {{emitter: !NodeJS.EventEmitter, eventName: string, handler: function(?)}}
    */
   static addEventListener(emitter, eventName, handler) {
     emitter.on(eventName, handler);
@@ -176,7 +175,7 @@ class Helper {
   }
 
   /**
-   * @param {!Array<{emitter: !EventEmitter, eventName: string, handler: function(?)}>}
+   * @param {!Array<{emitter: !NodeJS.EventEmitter, eventName: string, handler: function(?)}>} listeners
    */
   static removeEventListeners(listeners) {
     for (const listener of listeners)
diff --git a/package.json b/package.json
index 77be8a1f..23811393 100644
--- a/package.json
+++ b/package.json
@@ -13,12 +13,13 @@
     "test-doclint": "jasmine utils/doclint/check_public_api/test/test.js && jasmine utils/doclint/preprocessor/test.js",
     "test": "npm run lint --silent && npm run coverage && npm run test-doclint && npm run test-node6-transformer",
     "install": "node install.js",
-    "lint": "([ \"$CI\" = true ] && eslint --quiet -f codeframe . || eslint .) && npm run doc",
+    "lint": "([ \"$CI\" = true ] && eslint --quiet -f codeframe . || eslint .) && npm run tsc && npm run doc",
     "doc": "node utils/doclint/cli.js",
     "coverage": "COVERAGE=true npm run unit",
     "test-node6-transformer": "jasmine utils/node6-transform/test/test.js",
     "build": "node utils/node6-transform/index.js",
-    "unit-node6": "jasmine node6-test/test.js"
+    "unit-node6": "jasmine node6-test/test.js",
+    "tsc": "tsc -p ."
   },
   "author": "The Chromium Authors",
   "license": "Apache-2.0",
@@ -36,6 +37,12 @@
     "chromium_revision": "503964"
   },
   "devDependencies": {
+    "@types/debug": "0.0.30",
+    "@types/extract-zip": "^1.6.2",
+    "@types/mime": "^1.3.1",
+    "@types/node": "^8.0.26",
+    "@types/rimraf": "^2.0.2",
+    "@types/ws": "^3.0.2",
     "commonmark": "^0.27.0",
     "eslint": "^4.0.0",
     "esprima": "^4.0.0",
@@ -46,6 +53,7 @@
     "pdfjs-dist": "^1.8.595",
     "pixelmatch": "^4.0.2",
     "pngjs": "^3.2.0",
-    "text-diff": "^1.0.1"
+    "text-diff": "^1.0.1",
+    "typescript": "next"
   }
 }
diff --git a/tsconfig.json b/tsconfig.json
new file mode 100644
index 00000000..b5b9516c
--- /dev/null
+++ b/tsconfig.json
@@ -0,0 +1,11 @@
+{
+  "compilerOptions": {
+    "noEmit": true,
+    "allowJs": true,
+    "checkJs": true,
+    "target": "es2017"
+  },
+  "include": [
+    "lib"
+  ]
+}
diff --git a/utils/ChromiumDownloader.js b/utils/ChromiumDownloader.js
index 6992d991..a0e6237a 100644
--- a/utils/ChromiumDownloader.js
+++ b/utils/ChromiumDownloader.js
@@ -22,7 +22,9 @@ const extract = require('extract-zip');
 const util = require('util');
 const URL = require('url');
 const removeRecursive = require('rimraf');
+// @ts-ignore
 const ProxyAgent = require('https-proxy-agent');
+// @ts-ignore
 const getProxyForUrl = require('proxy-from-env').getProxyForUrl;
 
 const DOWNLOADS_FOLDER = path.join(__dirname, '..', '.local-chromium');
@@ -144,7 +146,7 @@ module.exports = {
     else if (platform === 'win32' || platform === 'win64')
       executablePath = path.join(folderPath, 'chrome-win32', 'chrome.exe');
     else
-      throw 'Unsupported platfrom: ' + platfrom;
+      throw 'Unsupported platfrom: ' + platform;
     return {
       executablePath,
       folderPath,
@@ -202,7 +204,7 @@ function downloadFile(url, destinationPath, progressCallback) {
     file.on('finish', () => fulfill());
     file.on('error', error => reject(error));
     response.pipe(file);
-    const totalBytes = parseInt(response.headers['content-length'], 10);
+    const totalBytes = parseInt(/** @type {string} */ (response.headers['content-length']), 10);
     if (progressCallback)
       response.on('data', onData.bind(null, totalBytes));
   });
@@ -224,11 +226,13 @@ function extractZip(zipPath, folderPath) {
 }
 
 function requestOptions(url, method = 'GET') {
+  /** @type {Object} */
   const result = URL.parse(url);
   result.method = method;
 
   const proxyURL = getProxyForUrl(url);
   if (proxyURL) {
+    /** @type {Object} */
     const parsedProxyURL = URL.parse(proxyURL);
     parsedProxyURL.secureProxy = parsedProxyURL.protocol === 'https:';
 
diff --git a/utils/doclint/check_public_api/JSBuilder.js b/utils/doclint/check_public_api/JSBuilder.js
index 26c77a79..8bec50b3 100644
--- a/utils/doclint/check_public_api/JSBuilder.js
+++ b/utils/doclint/check_public_api/JSBuilder.js
@@ -86,13 +86,13 @@ class JSOutline {
     }
     const args = [];
     for (const param of node.value.params) {
-      if (param.type === 'AssignmentPattern')
+      if (param.type === 'AssignmentPattern' && param.left.name)
         args.push(new Documentation.Argument(param.left.name));
       else if (param.type === 'RestElement')
         args.push(new Documentation.Argument('...' + param.argument.name));
       else if (param.type === 'Identifier')
         args.push(new Documentation.Argument(param.name));
-      else if (param.type === 'ObjectPattern')
+      else if (param.type === 'ObjectPattern' || param.type === 'AssignmentPattern')
         args.push(new Documentation.Argument('options'));
       else
         this.errors.push(`JS Parsing issue: unsupported syntax to define parameter in ${this._currentClassName}.${methodName}(): ${this._extractText(param)}`);
diff --git a/yarn.lock b/yarn.lock
index 507e65c5..fde13bed 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2,6 +2,46 @@
 # yarn lockfile v1
 
 
+"@types/debug@0.0.30":
+  version "0.0.30"
+  resolved "https://registry.yarnpkg.com/@types/debug/-/debug-0.0.30.tgz#dc1e40f7af3b9c815013a7860e6252f6352a84df"
+
+"@types/extract-zip@^1.6.2":
+  version "1.6.2"
+  resolved "https://registry.yarnpkg.com/@types/extract-zip/-/extract-zip-1.6.2.tgz#5c7eb441c41136167a42b88b64051e6260c29e86"
+
+"@types/glob@*":
+  version "5.0.32"
+  resolved "https://registry.yarnpkg.com/@types/glob/-/glob-5.0.32.tgz#aec5cfe987c72f099fdb1184452986aa506d5e8f"
+  dependencies:
+    "@types/minimatch" "*"
+    "@types/node" "*"
+
+"@types/mime@^1.3.1":
+  version "1.3.1"
+  resolved "https://registry.yarnpkg.com/@types/mime/-/mime-1.3.1.tgz#2cf42972d0931c1060c7d5fa6627fce6bd876f2f"
+
+"@types/minimatch@*":
+  version "3.0.1"
+  resolved "https://registry.yarnpkg.com/@types/minimatch/-/minimatch-3.0.1.tgz#b683eb60be358304ef146f5775db4c0e3696a550"
+
+"@types/node@*", "@types/node@^8.0.26":
+  version "8.0.26"
+  resolved "https://registry.yarnpkg.com/@types/node/-/node-8.0.26.tgz#4d58be925306fd22b1141085535a0268b8beb189"
+
+"@types/rimraf@^2.0.2":
+  version "2.0.2"
+  resolved "https://registry.yarnpkg.com/@types/rimraf/-/rimraf-2.0.2.tgz#7f0fc3cf0ff0ad2a99bb723ae1764f30acaf8b6e"
+  dependencies:
+    "@types/glob" "*"
+    "@types/node" "*"
+
+"@types/ws@^3.0.2":
+  version "3.0.2"
+  resolved "https://registry.yarnpkg.com/@types/ws/-/ws-3.0.2.tgz#b538b6a16daee454ac04054991271f3da38772de"
+  dependencies:
+    "@types/node" "*"
+
 acorn-jsx@^3.0.0:
   version "3.0.1"
   resolved "https://registry.yarnpkg.com/acorn-jsx/-/acorn-jsx-3.0.1.tgz#afdf9488fb1ecefc8348f6fb22f464e32a58b36b"
@@ -1070,6 +1110,10 @@ typedarray@^0.0.6:
   version "0.0.6"
   resolved "https://registry.yarnpkg.com/typedarray/-/typedarray-0.0.6.tgz#867ac74e3864187b1d3d47d996a78ec5c8830777"
 
+typescript@next:
+  version "2.6.0-dev.20171007"
+  resolved "https://registry.yarnpkg.com/typescript/-/typescript-2.6.0-dev.20171007.tgz#feead6b2bd906771c95fb8ae27e146d5b5ff6cd6"
+
 ultron@~1.1.0:
   version "1.1.0"
   resolved "https://registry.yarnpkg.com/ultron/-/ultron-1.1.0.tgz#b07a2e6a541a815fc6a34ccd4533baec307ca864"