puppeteer/website/versioned_docs/version-18.2.1/faq.md

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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 our [contributing guide](https://pptr.dev/contributing).

## Q: What is the status of cross-browser support?

Official Firefox support is currently experimental. The ongoing collaboration with Mozilla aims to support common end-to-end testing use cases, for which developers expect cross-browser coverage. The Puppeteer team needs input from users to stabilize Firefox support and to bring missing APIs to our attention.

From Puppeteer v2.1.0 onwards you can specify [`puppeteer.launch({product: 'firefox'})`](https://pptr.dev/api/puppeteer.puppeteernode.launch) to run your Puppeteer scripts in Firefox Nightly, without any additional custom patches. While [an older experiment](https://www.npmjs.com/package/puppeteer-firefox) required a patched version of Firefox, [the current approach](https://wiki.mozilla.org/Remote) works with “stock” Firefox.

We will continue to collaborate with other browser vendors to bring Puppeteer support to browsers such as Safari.
This effort includes exploration of a standard for executing cross-browser commands (instead of relying on the non-standard DevTools Protocol used by Chrome).

## 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/puppeteer/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/puppeteer/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/puppeteer/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?

Find the version using one of the following ways:

- Look for the `chromium` entry in [revisions.ts](https://github.com/puppeteer/puppeteer/blob/main/src/revisions.ts). To find the corresponding Chromium commit and version number, search for the revision prefixed by an `r` in [OmahaProxy](https://omahaproxy.appspot.com/)'s "Find Releases" section.
- Look for the `versionsPerRelease` map in [versions.js](https://github.com/puppeteer/puppeteer/blob/main/versions.js) which contains mapping between Chromium and the smallest Puppeteer version that supports it.

## Q: Which Firefox version does Puppeteer use?

Since Firefox support is experimental, Puppeteer downloads the latest [Firefox Nightly](https://wiki.mozilla.org/Nightly) when the `PUPPETEER_PRODUCT` environment variable is set to `firefox`. That's also why the value of `firefox` in [revisions.ts](https://github.com/puppeteer/puppeteer/blob/main/src/revisions.ts) is `latest` -- Puppeteer isn't tied to a particular Firefox version.

To fetch Firefox Nightly as part of Puppeteer installation:

```bash
PUPPETEER_PRODUCT=firefox npm i puppeteer
# or "yarn add puppeteer"
```

#### 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:

```ts
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/puppeteer/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://pptr.dev/api/puppeteer.launchoptions.executablepath). 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. Where should I look for help?

We have a [troubleshooting](https://github.com/puppeteer/puppeteer/blob/main/docs/troubleshooting.md) guide for various operating systems that lists the required dependencies.

#### Q: Chromium gets downloaded on every `npm ci` run. How can I cache the download?

The default download path is `node_modules/puppeteer/.local-chromium`. However, you can change that path with the `PUPPETEER_DOWNLOAD_PATH` environment variable.

Puppeteer uses that variable to resolve the Chromium executable location during launch, so you don’t need to specify `PUPPETEER_EXECUTABLE_PATH` as well.

For example, if you wish to keep the Chromium download in `~/.npm/chromium`:

```sh
export PUPPETEER_DOWNLOAD_PATH=~/.npm/chromium
npm ci

# by default the Chromium executable path is inferred
# from the download path
npm test

# a new run of npm ci will check for the existence of
# Chromium in ~/.npm/chromium
npm ci
```

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

There are many ways to get help on Puppeteer:

- [bugtracker](https://github.com/puppeteer/puppeteer/issues)
- [Stack Overflow](https://stackoverflow.com/questions/tagged/puppeteer)

Make sure to search these channels before posting your question.