Using Puppeteer for Easy Control Over Headless Chrome

November 07, 2017 0 Comments

Using Puppeteer for Easy Control Over Headless Chrome

 

 

How about an easy way to programmatically navigate to different pages, take screenshots, scrape website content, produce PDFs and run tests? It’s now quite easy to do using a new library by the Chrome team, Puppeteer, a Node.js library that abstracts the Chrome DevTools protocol.

Getting Started

The fastest way to get started is to use Try Puppeteer, a tool that allows to play with Puppeteer right in your browser.

If you want to explore Puppeteer for anything more serious than just playing around, you’ll want to actually add the library to your Node project using Yarn or npm:

$ yarn add puppeteer # or, using npm:
$ npm install puppeteer

Then, all you have to do is require puppeteer and you’ll be ready to get down to business:

index.js

'use strict'; const puppeteer = require('puppeteer');

Usage

Evaluating Elements

Here’s a simple Hello World example using Puppeteer to go to the Wikipedia article about Hello World, extract the first paragraph of the article and output the result to the console:

'use strict'; const puppeteer = require('puppeteer'); async function helloWorld() { const browser = await puppeteer.launch(); const page = await browser.newPage(); await page.goto('https://en.wikipedia.org/wiki/%22Hello,World!%22program'); const firstPar = await page.$eval('#mw-content-text p', el => el.innerText); console.log(firstPar); // A "Hello, World!" program is a computer program that outputs ... await browser.close();
} helloWorld();

Given that Puppeteer exposes a promise-based API, it’s easy to use async functions to define series of steps to follow.

In the above we used $eval on the page instance to get the first element that matches our selector and then extract its inner text. Pages also have the $$eval method to select all the elements that match the selector.

There’s also the $ and $$ methods, which are analogous, but return an elementHandle instead. Element handles can be clicked or tapped.

Taking Screenshots

Using Puppeteer to take a screenshot of a page or an element is just as easy. Here’s a simple example that takes a screenshot of Alligator.io’s home page and saves it to disk:

async function takeScreenshot() { const browser = await puppeteer.launch(); const page = await browser.newPage(); await page.goto('https://alligator.io/'); await page.screenshot({ path: 'hello-alligator.png' }); await browser.close();
} takeScreenshot();

🎩 Pretty magical if you ask me! Now say that you’re not happy with that screenshot. You want a lower quality Jpeg image instead and you want to also control the exact sizing of the viewport. That’s easily done with just a few more options:

async function takeScreenshot() { const browser = await puppeteer.launch(); const page = await browser.newPage(); await page.goto('https://alligator.io/'); await page.setViewport({ width: 1440, height: 900 }); await page.screenshot({ path: 'hello-alligator.jpg', type: 'jpeg', quality: 20 }); await browser.close();
} takeScreenshot();

Generating PDFs is also just as easy:

async function pdf() { const browser = await puppeteer.launch(); const page = await browser.newPage(); await page.goto('https://alligator.io/'); await page.pdf({ path: 'hello-alligator.pdf' }); await browser.close();
} pdf();

Interacting With the Page

Given that we’re effectively controlling a real Chrome browser instance under the hood, we can also interact with a page by, for example, filling form fields and clicking on elements.

Here’s an example that performs the following steps:

  • Go the Alligator.io’s homepage
  • Place the focus into the search input
  • Wait for 1 second
  • Type-in the word Fancy width a delay of 150ms between keystrokes
  • Wait for the page to have an element with a class of algolia__results
  • Take a screenshot

'use strict'; const puppeteer = require('puppeteer'); async function performSearch() { const browser = await puppeteer.launch(); const page = await browser.newPage(); await page.goto('https://alligator.io/'); await page.focus('.algoliainput'); await page.waitFor(1000); await page.type('.algoliainput', 'Fancy', { delay: 150 }); await page.waitForSelector('.algolia__results'); await page.screenshot({ path: 'search.png' }); await browser.close();
} performSearch();

Here's the resulting screenshot...

Screenshot taking using Puppeteer

🤖 This post barely scratched the surface with what's possible with headless Chrome and Puppeteer. Refer to the extensive API docs to dig deeper.


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