Puppeteer in Dart

A Dart library to automate the Chrome browser over the DevTools Protocol.

This is a port of the Puppeteer Node.JS library in the Dart language.

What can I do?

Most things that you can do manually in the browser can be done using Puppeteer! Here are a few examples to get you started:

• Generate screenshots and PDFs of pages.
• Crawl a SPA (Single-Page Application) and generate pre-rendered content (i.e. "SSR" (Server-Side Rendering)).
• Automate form submission, UI testing, keyboard input, etc.
• Create an up-to-date, automated testing environment. Run your tests directly in the latest version of Chrome using the latest JavaScript and browser features.

API

• See the full API in a single-page document: doc/api.md
• See the Dart Doc for this package: API reference
• The Dart version of Puppeteer is very similar to the original Javascript code. Every sample available for Puppeteer Node.JS could be converted in Dart very easily.

Examples

• Launch chrome
• Generate a PDF from an HTML page
• Take a screenshot of a page
• Take a screenshot of an element in a page
• Create a static version of a Single Page Application
• Capture a screencast of the page
• Execute JavaScript code

Launch Chrome

Download the last revision of chrome and launch it.

import 'package:puppeteer/puppeteer.dart';

void main() async {
  // Download the Chromium binaries, launch it and connect to the "DevTools"
  var browser = await puppeteer.launch();

  // Open a new tab
  var myPage = await browser.newPage();

  // Go to a page and wait to be fully loaded
  await myPage.goto('https://dart.dev', wait: Until.networkIdle);

  // Do something... See other examples
  await myPage.screenshot();
  await myPage.pdf();
  await myPage.evaluate('() => document.title');

  // Gracefully close the browser's process
  await browser.close();
}

Generate a PDF from a page

import 'dart:io';
import 'package:puppeteer/puppeteer.dart';

void main() async {
  // Start the browser and go to a web page
  var browser = await puppeteer.launch();
  var page = await browser.newPage();
  await page.goto('https://dart.dev', wait: Until.networkIdle);

  // For this example, we force the "screen" media-type because sometime
  // CSS rules with "@media print" can change the look of the page.
  await page.emulateMediaType(MediaType.screen);

  // Capture the PDF and save it to a file.
  await page.pdf(
      format: PaperFormat.a4,
      printBackground: true,
      pageRanges: '1',
      output: File('example/_dart.pdf').openWrite());
  await browser.close();
}

Take a screenshot of a complete HTML page

import 'dart:io';
import 'package:puppeteer/puppeteer.dart';

void main() async {
  // Start the browser and go to a web page
  var browser = await puppeteer.launch();
  var page = await browser.newPage();

  // Setup the dimensions and user-agent of a particular phone
  await page.emulate(puppeteer.devices.pixel2XL);

  await page.goto('https://dart.dev', wait: Until.networkIdle);

  // Take a screenshot of the page
  var screenshot = await page.screenshot();

  // Save it to a file
  await File('example/_github.png').writeAsBytes(screenshot);

  await browser.close();
}

Take a screenshot of a specific node in the page

import 'dart:io';
import 'package:puppeteer/puppeteer.dart';

void main() async {
  // Start the browser and go to a web page
  var browser = await puppeteer.launch();
  var page = await browser.newPage();
  await page.goto('https://stackoverflow.com/', wait: Until.networkIdle);

  // Select an element on the page
  var form = await page.$('input[name="q"]');

  // Take a screenshot of the element
  var screenshot = await form.screenshot();

  // Save it to a file
  await File('example/_element.png').writeAsBytes(screenshot);

  await browser.close();
}

Interact with the page and scrap content

import 'package:puppeteer/puppeteer.dart';

void main() async {
  var browser = await puppeteer.launch();
  var page = await browser.newPage();

  await page.goto('https://developers.google.com/web/',
      wait: Until.networkIdle);

  // Type into search box.
  await page.type('.devsite-search-field', 'Headless Chrome');

  // Wait for suggest overlay to appear and click "show all results".
  var allResultsSelector = '.devsite-suggest-all-results';
  await page.waitForSelector(allResultsSelector);
  await page.click(allResultsSelector);

  // Wait for the results page to load and display the results.
  const resultsSelector = '.gsc-results .gsc-thumbnail-inside a.gs-title';
  await page.waitForSelector(resultsSelector);

  // Extract the results from the page.
  var links = await page.evaluate(r'''resultsSelector => {
  const anchors = Array.from(document.querySelectorAll(resultsSelector));
  return anchors.map(anchor => {
    const title = anchor.textContent.split('|')[0].trim();
    return `${title} - ${anchor.href}`;
  });
}''', args: [resultsSelector]);
  print(links.join('\n'));

  await browser.close();
}

Create a static version of a Single Page Application

import 'package:puppeteer/puppeteer.dart';

void main() async {
  var browser = await puppeteer.launch();
  var page = await browser.newPage();
  await page.goto('https://w3c.github.io/');

  // Either use the helper to get the content
  var pageContent = await page.content;
  print(pageContent);

  // Or get the content directly by executing some Javascript
  var pageContent2 = await page.evaluate('document.documentElement.outerHTML');
  print(pageContent2);

  await browser.close();
}

Capture a screencast of the page

The screencast feature is not part of the Puppeteer API. This example uses the low-level protocol API to send the commands to the browser.

import 'dart:convert';
import 'dart:io';
import 'package:image/image.dart' as image;
import 'package:puppeteer/puppeteer.dart';
import 'package:shelf/shelf_io.dart' as io;
import 'package:shelf_static/shelf_static.dart';

void main() async {
  // Start a local web server and open the page
  var server =
      await io.serve(createStaticHandler('example/html'), 'localhost', 0);
  var browser = await puppeteer.launch();
  var page = await browser.newPage();
  await page.goto('http://localhost:${server.port}/rubiks_cube/index.html');

  // On each frame, decode the image and use the "image" package to create an
  // animated gif.
  var animation = image.Animation();
  page.devTools.page.onScreencastFrame.listen((event) {
    var frame = image.decodePng(base64.decode(event.data));
    if (frame != null) {
      animation.addFrame(frame);
    }
  });

  // For this example, we change the CSS animations speed.
  await page.devTools.animation.setPlaybackRate(240);

  // Start the screencast
  await page.devTools.page.startScreencast(maxWidth: 150, maxHeight: 150);

  // Wait a few seconds and stop the screencast.
  await Future.delayed(Duration(seconds: 3));
  await page.devTools.page.stopScreencast();

  // Encode all the frames in an animated Gif file.
  File('example/_rubkis_cube.gif')
      .writeAsBytesSync(image.GifEncoder().encodeAnimation(animation)!);

  // Alternatively, we can save all the frames on disk and use ffmpeg to convert
  // it to a video file. (for example: ffmpeg -i frames/%3d.png -r 10 output.mp4)

  await browser.close();
  await server.close(force: true);
}

Low-level DevTools protocol

This package contains a fully typed API of the Chrome DevTools protocol. The code is generated from the JSON Schema provided by Chrome.

With this API you have access to the entire capabilities of Chrome DevTools.

The code is in lib/protocol

import 'package:puppeteer/puppeteer.dart';

void main() async {
  var browser = await puppeteer.launch();
  // Create a chrome's tab
  var page = await browser.newPage();

  // You can access the entire Chrome DevTools protocol.
  // This is useful to access information not exposed by the Puppeteer API
  // Be aware that this is a low-level, complex API.
  // Documentation of the protocol: https://chromedevtools.github.io/devtools-protocol/

  // Examples:

  // Start a screencast
  await page.devTools.page.startScreencast();

  // Change the animation speed for the document
  await page.devTools.animation.setPlaybackRate(10);

  // Access the memory information for the page
  await page.devTools.memory.getDOMCounters();

  // Go to https://chromedevtools.github.io/devtools-protocol/ to read more about
  // the protocol and use the code in `lib/protocol`.

  await browser.close();
}

Execute JavaScript code

The Puppeteer API exposes several functions to run some Javascript code in the browser.

Like in this example from the official Node.JS library:

test(async () => {
  const result = await page.evaluate(x => {
    return Promise.resolve(8 * x);
  }, 7);
});

In the Dart port, you have to pass the JavaScript code as a string. The example above will be written as:

main() async {
  var result = await page.evaluate('''x => {
    return Promise.resolve(8 * x);
  }''', args: [7]);
}

The javascript code can be:

• A function declaration (in the classical form with the function keyword or with the shorthand format (() =>))
• An expression. In which case you cannot pass any arguments to the evaluate method.

import 'package:puppeteer/puppeteer.dart';

void main() async {
  var browser = await puppeteer.launch();
  var page = await browser.newPage();

  // function declaration syntax
  await page.evaluate('function(x) { return x > 0; }', args: [7]);

  // shorthand syntax
  await page.evaluate('(x) => x > 0', args: [7]);

  // Multi line shorthand syntax
  await page.evaluate('''(x) => {  
    return x > 0;
  }''', args: [7]);

  // shorthand syntax with async
  await page.evaluate('''async (x) => {
    return await x;
  }''', args: [7]);

  // An expression.
  await page.evaluate('document.body');

  await browser.close();
}

If you are using IntellJ (or Webstorm), you can enable the syntax highlighter and the code-analyzer for the Javascript snippet with a comment like // language=js before the string.

main() {
  page.evaluate(
  //language=js
  '''function _(x) {
    return x > 0;
  }''', args: [7]);
}

Note: In a future version, we can imagine writing the code in Dart and it would be compiled to javascript transparently (with ddc or dart2js).

Related work

• chrome-remote-interface
• puppeteer
• webkit_inspection_protocol
• dart webdriver