puppeteer/README.md

# Puppeteer

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###### [API](https://github.com/GoogleChrome/puppeteer/blob/v1.15.0/docs/api.md) | [FAQ](#faq) | [Contributing](https://github.com/GoogleChrome/puppeteer/blob/master/CONTRIBUTING.md) | [Troubleshooting](https://github.com/GoogleChrome/puppeteer/blob/master/docs/troubleshooting.md)

> Puppeteer is a Node library which provides a high-level API to control Chrome or Chromium over the [DevTools Protocol](https://chromedevtools.github.io/devtools-protocol/). Puppeteer runs [headless](https://developers.google.com/web/updates/2017/04/headless-chrome) by default, but can be configured to run full (non-headless) Chrome or Chromium.

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###### 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.
* Capture a [timeline trace](https://developers.google.com/web/tools/chrome-devtools/evaluate-performance/reference) of your site to help diagnose performance issues.
* Test Chrome Extensions.
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Give it a spin: https://try-puppeteer.appspot.com/

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## Getting Started

### Installation

To use Puppeteer in your project, run:

```bash
npm i puppeteer
# or "yarn add puppeteer"
```

Note: When you install Puppeteer, it downloads a recent version of Chromium (~170MB Mac, ~282MB Linux, ~280MB Win) that is guaranteed to work with the API. To skip the download, see [Environment variables](https://github.com/GoogleChrome/puppeteer/blob/v1.15.0/docs/api.md#environment-variables).


### puppeteer-core

Since version 1.7.0 we publish the [`puppeteer-core`](https://www.npmjs.com/package/puppeteer-core) package,
a version of Puppeteer that doesn't download Chromium by default.

```bash
npm i puppeteer-core
# or "yarn add puppeteer-core"
```

`puppeteer-core` is intended to be a lightweight version of Puppeteer for launching an existing browser installation or for connecting to a remote one. Be sure that the version of puppeteer-core you install is compatible with the
browser you intend to connect to.

See [puppeteer vs puppeteer-core](https://github.com/GoogleChrome/puppeteer/blob/master/docs/api.md#puppeteer-vs-puppeteer-core).

### Usage

Note: Puppeteer requires at least Node v6.4.0, but the examples below use async/await which is only supported in Node v7.6.0 or greater.

Puppeteer will be familiar to people using other browser testing frameworks. You create an instance
of `Browser`, open pages, and then manipulate them with [Puppeteer's API](https://github.com/GoogleChrome/puppeteer/blob/v1.15.0/docs/api.md#).

**Example** - navigating to https://example.com and saving a screenshot as *example.png*:

Save file as **example.js**

```js
const puppeteer = require('puppeteer');

(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  await page.goto('https://example.com');
  await page.screenshot({path: 'example.png'});

  await browser.close();
})();
```

Execute script on the command line

```bash
node example.js
```

Puppeteer sets an initial page size to 800px x 600px, which defines the screenshot size. The page size can be customized  with [`Page.setViewport()`](https://github.com/GoogleChrome/puppeteer/blob/v1.15.0/docs/api.md#pagesetviewportviewport).

**Example** - create a PDF.

Save file as **hn.js**

```js
const puppeteer = require('puppeteer');

(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  await page.goto('https://news.ycombinator.com', {waitUntil: 'networkidle2'});
  await page.pdf({path: 'hn.pdf', format: 'A4'});

  await browser.close();
})();
```

Execute script on the command line

```bash
node hn.js
```

See [`Page.pdf()`](https://github.com/GoogleChrome/puppeteer/blob/v1.15.0/docs/api.md#pagepdfoptions) for more information about creating pdfs.

**Example** - evaluate script in the context of the page

Save file as **get-dimensions.js**

```js
const puppeteer = require('puppeteer');

(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  await page.goto('https://example.com');

  // Get the "viewport" of the page, as reported by the page.
  const dimensions = await page.evaluate(() => {
    return {
      width: document.documentElement.clientWidth,
      height: document.documentElement.clientHeight,
      deviceScaleFactor: window.devicePixelRatio
    };
  });

  console.log('Dimensions:', dimensions);

  await browser.close();
})();
```

Execute script on the command line

```bash
node get-dimensions.js
```

See [`Page.evaluate()`](https://github.com/GoogleChrome/puppeteer/blob/v1.15.0/docs/api.md#pageevaluatepagefunction-args) for more information on `evaluate` and related methods like `evaluateOnNewDocument` and `exposeFunction`.

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## Default runtime settings

**1. Uses Headless mode**

Puppeteer launches Chromium in [headless mode](https://developers.google.com/web/updates/2017/04/headless-chrome). To launch a full version of Chromium, set the ['headless' option](https://github.com/GoogleChrome/puppeteer/blob/v1.15.0/docs/api.md#puppeteerlaunchoptions) when launching a browser:

```js
const browser = await puppeteer.launch({headless: false}); // default is true
```

**2. Runs a bundled version of Chromium**

By default, Puppeteer downloads and uses a specific version of Chromium so its API
is guaranteed to work out of the box. To use Puppeteer with a different version of Chrome or Chromium,
pass in the executable's path when creating a `Browser` instance:

```js
const browser = await puppeteer.launch({executablePath: '/path/to/Chrome'});
```

See [`Puppeteer.launch()`](https://github.com/GoogleChrome/puppeteer/blob/v1.15.0/docs/api.md#puppeteerlaunchoptions) for more information.

See [`this article`](https://www.howtogeek.com/202825/what%E2%80%99s-the-difference-between-chromium-and-chrome/) for a description of the differences between Chromium and Chrome. [`This article`](https://chromium.googlesource.com/chromium/src/+/master/docs/chromium_browser_vs_google_chrome.md) describes some differences for Linux users.

**3. Creates a fresh user profile**

Puppeteer creates its own Chromium user profile which it **cleans up on every run**.

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## Resources

- [API Documentation](https://github.com/GoogleChrome/puppeteer/blob/v1.15.0/docs/api.md)
- [Examples](https://github.com/GoogleChrome/puppeteer/tree/master/examples/)
- [Community list of Puppeteer resources](https://github.com/transitive-bullshit/awesome-puppeteer)


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## Debugging tips

1. Turn off headless mode - sometimes it's useful to see what the browser is
   displaying. Instead of launching in headless mode, launch a full version of
   the browser using  `headless: false`:

        const browser = await puppeteer.launch({headless: false});

2. Slow it down - the `slowMo` option slows down Puppeteer operations by the
   specified amount of milliseconds. It's another way to help see what's going on.

        const browser = await puppeteer.launch({
          headless: false,
          slowMo: 250 // slow down by 250ms
        });

3. Capture console output - You can listen for the `console` event.
   This is also handy when debugging code in `page.evaluate()`:

        page.on('console', msg => console.log('PAGE LOG:', msg.text()));

        await page.evaluate(() => console.log(`url is ${location.href}`));

4. Stop test execution and use a debugger in browser

  - Use `{devtools: true}` when launching Puppeteer:

      `const browser = await puppeteer.launch({devtools: true});`

  - Change default test timeout:

      jest: `jest.setTimeout(100000);`

      jasmine: `jasmine.DEFAULT_TIMEOUT_INTERVAL = 100000;`

      mocha: `this.timeout(100000);` (don't forget to change test to use [function and not '=>'](https://stackoverflow.com/a/23492442))

  - Add an evaluate statement with `debugger` inside / add  `debugger` to an existing evaluate statement:

    `await page.evaluate(() => {debugger;});`

     The test will now stop executing in the above evaluate statement, and chromium will stop in debug mode.

5. Enable verbose logging - internal DevTools protocol traffic
   will be logged via the [`debug`](https://github.com/visionmedia/debug) module under the `puppeteer` namespace.

        # Basic verbose logging
        env DEBUG="puppeteer:*" node script.js

        # Protocol traffic can be rather noisy. This example filters out all Network domain messages
        env DEBUG="puppeteer:*" env DEBUG_COLORS=true node script.js 2>&1 | grep -v '"Network'

6. Debug your Puppeteer (node) code easily, using [ndb](https://github.com/GoogleChromeLabs/ndb)

  - `npm install -g ndb` (or even better, use [npx](https://github.com/zkat/npx)!)

  - add a `debugger` to your Puppeteer (node) code

  - add `ndb` (or `npx ndb`) before your test command. For example:

    `ndb jest` or `ndb mocha` (or `npx ndb jest` / `npx ndb mocha`)

  - debug your test inside chromium like a boss!


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## Contributing to Puppeteer

Check out [contributing guide](https://github.com/GoogleChrome/puppeteer/blob/master/CONTRIBUTING.md) to get an overview of Puppeteer development.

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# FAQ

#### Q: Who maintains Puppeteer?

The Chrome DevTools team maintains the library, but we'd love your help and expertise on the project!
See [Contributing](https://github.com/GoogleChrome/puppeteer/blob/master/CONTRIBUTING.md).

#### Q: What are Puppeteer’s goals and principles?

The goals of the project are:

- Provide a slim, canonical library that highlights the capabilities of the [DevTools Protocol](https://chromedevtools.github.io/devtools-protocol/).
- Provide a reference implementation for similar testing libraries. Eventually, these other frameworks could adopt Puppeteer as their foundational layer.
- Grow the adoption of headless/automated browser testing.
- Help dogfood new DevTools Protocol features...and catch bugs!
- Learn more about the pain points of automated browser testing and help fill those gaps.

We adapt [Chromium principles](https://www.chromium.org/developers/core-principles) to help us drive product decisions:
- **Speed**: Puppeteer has almost zero performance overhead over an automated page.
- **Security**: Puppeteer operates off-process with respect to Chromium, making it safe to automate potentially malicious pages.
- **Stability**: Puppeteer should not be flaky and should not leak memory.
- **Simplicity**: Puppeteer provides a high-level API that’s easy to use, understand, and debug.

#### Q: Is Puppeteer replacing Selenium/WebDriver?

**No**. Both projects are valuable for very different reasons:
- Selenium/WebDriver focuses on cross-browser automation; its value proposition is a single standard API that works across all major browsers.
- Puppeteer focuses on Chromium; its value proposition is richer functionality and higher reliability.

That said, you **can** use Puppeteer to run tests against Chromium, e.g. using the community-driven [jest-puppeteer](https://github.com/smooth-code/jest-puppeteer). While this probably shouldn’t be your only testing solution, it does have a few good points compared to WebDriver:

- Puppeteer requires zero setup and comes bundled with the Chromium version it works best with, making it [very easy to start with](https://github.com/GoogleChrome/puppeteer/#getting-started). At the end of the day, it’s better to have a few tests running chromium-only, than no tests at all.
- Puppeteer has event-driven architecture, which removes a lot of potential flakiness. There’s no need for evil “sleep(1000)” calls in puppeteer scripts.
- Puppeteer runs headless by default, which makes it fast to run. Puppeteer v1.5.0 also exposes browser contexts, making it possible to efficiently parallelize test execution.
- Puppeteer shines when it comes to debugging: flip the “headless” bit to false, add “slowMo”, and you’ll see what the browser is doing. You can even open Chrome DevTools to inspect the test environment.

#### Q: Why doesn’t Puppeteer v.XXX work with Chromium v.YYY?

We see Puppeteer as an **indivisible entity** with Chromium. Each version of Puppeteer bundles a specific version of Chromium – **the only** version it is guaranteed to work with.

This is not an artificial constraint: A lot of work on Puppeteer is actually taking place in the Chromium repository. Here’s a typical story:
- A Puppeteer bug is reported: https://github.com/GoogleChrome/puppeteer/issues/2709
- It turned out this is an issue with the DevTools protocol, so we’re fixing it in Chromium: https://chromium-review.googlesource.com/c/chromium/src/+/1102154
- Once the upstream fix is landed, we roll updated Chromium into Puppeteer: https://github.com/GoogleChrome/puppeteer/pull/2769

However, oftentimes it is desirable to use Puppeteer with the official Google Chrome rather than Chromium. For this to work, you should install a `puppeteer-core` version that corresponds to the Chrome version.

For example, in order to drive Chrome 71 with puppeteer-core, use `chrome-71` npm tag:
```bash
npm install puppeteer-core@chrome-71
```

#### Q: Which Chromium version does Puppeteer use?

Look for `chromium_revision` in [package.json](https://github.com/GoogleChrome/puppeteer/blob/master/package.json).

#### Q: What’s considered a “Navigation”?

From Puppeteer’s standpoint, **“navigation” is anything that changes a page’s URL**.
Aside from regular navigation where the browser hits the network to fetch a new document from the web server, this includes [anchor navigations](https://www.w3.org/TR/html5/single-page.html#scroll-to-fragid) and [History API](https://developer.mozilla.org/en-US/docs/Web/API/History_API) usage.

With this definition of “navigation,” **Puppeteer works seamlessly with single-page applications.**

#### Q: What’s the difference between a “trusted" and "untrusted" input event?

In browsers, input events could be divided into two big groups: trusted vs. untrusted.

- **Trusted events**: events generated by users interacting with the page, e.g. using a mouse or keyboard.
- **Untrusted event**: events generated by Web APIs, e.g. `document.createEvent` or `element.click()` methods.

Websites can distinguish between these two groups:
- using an [`Event.isTrusted`](https://developer.mozilla.org/en-US/docs/Web/API/Event/isTrusted) event flag
- sniffing for accompanying events. For example, every trusted `'click'` event is preceded by `'mousedown'` and `'mouseup'` events.

For automation purposes it’s important to generate trusted events. **All input events generated with Puppeteer are trusted and fire proper accompanying events.** If, for some reason, one needs an untrusted event, it’s always possible to hop into a page context with `page.evaluate` and generate a fake event:

```js
await page.evaluate(() => {
  document.querySelector('button[type=submit]').click();
});
```

#### Q: What features does Puppeteer not support?

You may find that Puppeteer does not behave as expected when controlling pages that incorporate audio and video. (For example, [video playback/screenshots is likely to fail](https://github.com/GoogleChrome/puppeteer/issues/291).) There are two reasons for this:

* Puppeteer is bundled with Chromium--not Chrome--and so by default, it inherits all of [Chromium's media-related limitations](https://www.chromium.org/audio-video). This means that Puppeteer does not support licensed formats such as AAC or H.264. (However, it is possible to force Puppeteer to use a separately-installed version Chrome instead of Chromium via the [`executablePath` option to `puppeteer.launch`](https://github.com/GoogleChrome/puppeteer/blob/v1.15.0/docs/api.md#puppeteerlaunchoptions). You should only use this configuration if you need an official release of Chrome that supports these media formats.)
* Since Puppeteer (in all configurations) controls a desktop version of Chromium/Chrome, features that are only supported by the mobile version of Chrome are not supported. This means that Puppeteer [does not support HTTP Live Streaming (HLS)](https://caniuse.com/#feat=http-live-streaming).

#### Q: I am having trouble installing / running Puppeteer in my test environment?
We have a [troubleshooting](https://github.com/GoogleChrome/puppeteer/blob/master/docs/troubleshooting.md) guide for various operating systems that lists the required dependencies.

#### Q: How do I try/test a prerelease version of Puppeteer?

You can check out this repo or install the latest prerelease from npm:

```bash
npm i --save puppeteer@next
```

Please note that prerelease may be unstable and contain bugs.

#### Q: I have more questions! Where do I ask?

There are many ways to get help on Puppeteer:
- [bugtracker](https://github.com/GoogleChrome/puppeteer/issues)
- [stackoverflow](https://stackoverflow.com/questions/tagged/puppeteer)
- [slack channel](https://join.slack.com/t/puppeteer/shared_invite/enQtMzU4MjIyMDA5NTM4LTM1OTdkNDhlM2Y4ZGUzZDdjYjM5ZWZlZGFiZjc4MTkyYTVlYzIzYjU5NDIyNzgyMmFiNDFjN2UzNWU0N2ZhZDc)

Make sure to search these channels before posting your question.


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