feat: add Page.Events.DOMContentLoaded (#1730)

Fixes #1580

docs/api.md

@@ -30,6 +30,7 @@
 - [class: Page](#class-page)
   * [event: 'console'](#event-console)
   * [event: 'dialog'](#event-dialog)
+  * [event: 'domcontentloaded'](#event-domcontentloaded)
   * [event: 'error'](#event-error)
   * [event: 'frameattached'](#event-frameattached)
   * [event: 'framedetached'](#event-framedetached)
@@ -434,6 +435,10 @@ page.evaluate(() => console.log('hello', 5, {foo: 'bar'}));
 
 Emitted when a JavaScript dialog appears, such as `alert`, `prompt`, `confirm` or `beforeunload`. Puppeteer can respond to the dialog via [Dialog]'s [accept](#dialogacceptprompttext) or [dismiss](#dialogdismiss) methods.
 
+#### event: 'domcontentloaded'
+
+Emitted when the JavaScript [`DOMContentLoaded`](https://developer.mozilla.org/en-US/docs/Web/Events/DOMContentLoaded) event is dispatched.
+
 #### event: 'error'
 - <[Error]>
 

lib/Page.js

@@ -95,6 +95,7 @@ class Page extends EventEmitter {
     this._networkManager.on(NetworkManager.Events.RequestFailed, event => this.emit(Page.Events.RequestFailed, event));
     this._networkManager.on(NetworkManager.Events.RequestFinished, event => this.emit(Page.Events.RequestFinished, event));
 
+    client.on('Page.domContentEventFired', event => this.emit(Page.Events.DOMContentLoaded));
     client.on('Page.loadEventFired', event => this.emit(Page.Events.Load));
     client.on('Runtime.consoleAPICalled', event => this._onConsoleAPI(event));
     client.on('Page.javascriptDialogOpening', event => this._onDialog(event));
@@ -965,6 +966,7 @@ function convertPrintParameterToInches(parameter) {
 Page.Events = {
   Console: 'console',
   Dialog: 'dialog',
+  DOMContentLoaded: 'domcontentloaded',
   Error: 'error',
   // Can't use just 'error' due to node.js special treatment of error events.
   // @see https://nodejs.org/api/events.html#events_error_events

test/test.js

@@ -969,6 +969,13 @@ describe('Page', function() {
     });
   });
 
+  describe('Page.Events.DOMContentLoaded', function() {
+    it('should fire when expected', async({page, server}) => {
+      page.goto('about:blank');
+      await waitForEvents(page, 'domcontentloaded', 1);
+    });
+  });
+
   describe('Page.metrics', function() {
     it('should get metrics from a page', async({page, server}) => {
       await page.goto('about:blank');