puppeteer/docs/contributing.md

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Contributing

First of all, thank you for your interest in Puppeteer! We'd love to accept your patches and contributions!

Contributor License Agreement

Contributions to this project must be accompanied by a Contributor License Agreement. You (or your employer) retain the copyright to your contribution, this simply gives us permission to use and redistribute your contributions as part of the project. Head over to https://cla.developers.google.com/ to see your current agreements on file or to sign a new one.

You generally only need to submit a CLA once, so if you've already submitted one (even if it was for a different project), you probably don't need to do it again.

Getting Code

1. Clone this repository

git clone https://github.com/puppeteer/puppeteer
cd puppeteer

2. Install dependencies

npm install

3. Build and run Puppeteer tests locally. For more information about tests, read Running & Writing Tests.

npm run build && npm run test:chrome

Code reviews

All submissions, including submissions by project members, require review. We use GitHub pull requests for this purpose. Consult GitHub Help for more information on using pull requests.

Code Style

• Coding style is fully defined in .eslintrc and we automatically format our code with Prettier.
• It's recommended to set-up Prettier into your editor, or you can run npm run lint:eslint:fix to automatically format any files.
• If you're working in a JS file, code should be annotated with closure annotations.
• If you're working in a TS file, you should explicitly type all variables and return types. You'll get ESLint warnings if you don't so if you're not sure use them as guidelines, and feel free to ask us for help!

To run ESLint, use:

npm run lint:eslint

You can check your code by running:

npm run build

TypeScript guidelines

• Try to avoid the use of any when possible. Consider unknown as a better alternative. You are able to use any if needbe, but it will generate an ESLint warning.

Project structure and TypeScript compilation

The code in Puppeteer is split primarily into two folders:

• src contains all source code
• vendor contains all dependencies that we've vendored into the codebase. See the vendor/README.md for details.

We structure these using TypeScript's project references, which lets us treat each folder like a standalone TypeScript project.

Shipping CJS and ESM bundles

Currently Puppeteer ships both CommonJS and ESM, therefore we maintain two tsconfig files for each project: tsconfig.esm.json and tsconfig.cjs.json. At build time we compile twice, once outputting to CJS and another time to output to ESM.

We compile into the lib directory which is what we publish on the npm repository and it's structured like so:

lib
- cjs
  - puppeteer <== the output of compiling `src/tsconfig.cjs.json`
  - vendor <== the output of compiling `vendor/tsconfig.cjs.json`
- esm
  - puppeteer <== the output of compiling `src/tsconfig.esm.json`
  - vendor <== the output of compiling `vendor/tsconfig.esm.json`

tsconfig.ts for the tests

We also maintain test/tsconfig.json. This is only used to compile the unit test *.spec.ts files. When the tests are run, we first compile Puppeteer as normal before running the unit tests against the compiled output. Doing this lets the test run against the compiled code we ship to users so it gives us more confidence in our compiled output being correct.

Root tsconfig.json

The root tsconfig.json exists for the API Extractor; it has to find a tsconfig.json in the project's root directory. It is not used for anything else.

API guidelines

When authoring new API methods, consider the following:

• Expose as little information as needed. When in doubt, don’t expose new information.
• Methods are used in favor of getters/setters.
  • The only exception is namespaces, e.g. page.keyboard and page.coverage
• All string literals must be small case. This includes event names and option values.
• Avoid adding "sugar" API (API that is trivially implementable in user-space) unless they're very demanded.

Commit messages

Commit messages should follow the Conventional Commits format. This is enforced via npm run lint.

In particular, breaking changes should clearly be noted as “BREAKING CHANGE:” in the commit message footer. Example:

fix(page): fix page.pizza method

This patch fixes page.pizza so that it works with iframes.

Issues: #123, #234

BREAKING CHANGE: page.pizza now delivers pizza at home by default.
To deliver to a different location, use the "deliver" option:
  `page.pizza({deliver: 'work'})`.

Writing documentation

Documentation is generated via npm run docs. It is automatically published to our documentation site on merge and gets versioned on release.

Writing TSDoc comments

Each change to Puppeteer should be thoroughly documented using TSDoc comments. Refer to the API Extractor documentation for information on the exact syntax.

• Every new method needs to have either @public or @internal added as a tag depending on if it is part of the public API.
• Keep each line in a comment to no more than 90 characters (ESLint will warn you if you go over this). If you're a VSCode user the Rewrap plugin is highly recommended!

Running the documentation site locally

• In the Puppeteer's folder, install all dependencies with npm i.
• run npm run docs which will generate all the .md files on puppeteer/docs/api.
• run npm i on puppeteer/website.
• run npm start on puppeteer/website.

Adding new dependencies

For all dependencies (both installation and development):

• Do not add a dependency if the desired functionality is easily implementable.
• If adding a dependency, it should be well-maintained and trustworthy.

A barrier for introducing new installation dependencies is especially high:

• Do not add installation dependency unless it's critical to project success.

There are additional considerations for dependencies that are environment agonistic. See the vendor/README.md for details.

Running & Writing Tests

• Every feature should be accompanied by a test.
• Every public api event/method should be accompanied by a test.
• Tests should not depend on external services.
• Tests should work on all three platforms: Mac, Linux and Win. This is especially important for screenshot tests.

Puppeteer tests are located in the test directory and are written using Mocha. See test/README.md for more details.

Despite being named 'unit', these are integration tests, making sure public API methods and events work as expected.

• To run all tests:

npm run test:unit

• To run a specific test, substitute the it with it.only:

  ...
  it.only('should work', async function({server, page}) {
    const response = await page.goto(server.EMPTY_PAGE);
    expect(response.ok).toBe(true);
  });

• To disable a specific test, substitute the it with xit (mnemonic rule: 'cross it'):

  ...
  // Using "xit" to skip specific test
  xit('should work', async function({server, page}) {
    const response = await page.goto(server.EMPTY_PAGE);
    expect(response.ok).toBe(true);
  });

• To run tests in non-headless mode:

HEADLESS=false npm run test:unit

• To run Firefox tests, firstly ensure you have Firefox installed locally (you only need to do this once, not on every test run) and then you can run the tests:

PUPPETEER_PRODUCT=firefox node install.js
PUPPETEER_PRODUCT=firefox npm run test:unit

• To run experimental Chromium MacOS ARM tests, firstly ensure you have correct Chromium version installed locally (you only need to do this once, not on every test run) and then you can run the tests:

PUPPETEER_EXPERIMENTAL_CHROMIUM_MAC_ARM=1 node install.js
PUPPETEER_EXPERIMENTAL_CHROMIUM_MAC_ARM=1 npm run test:unit

• To run tests with custom browser executable:

BINARY=<path-to-executable> npm run test:unit

Public API Coverage

Every public API method or event should be called at least once in tests. To ensure this, there's a coverage command which tracks calls to public API and reports back if some methods/events were not called.

Run coverage:

npm run coverage

Debugging Puppeteer

See Debugging Tips in the readme.

For Project Maintainers

Rolling new Chromium version

The following steps are needed to update the Chromium version.

1. Find a suitable Chromium revision Not all revisions have builds for all platforms, so we need to find one that does. To do so, run utils/check_availability.js -rd to find the latest suitable dev Chromium revision (see utils/check_availability.js -help for more options).
2. Update src/revisions.ts with the found revision number.
3. Update versions.js with the new Chromium-to-Puppeteer version mapping and update lastMaintainedChromiumVersion with the latest stable Chrome version.
4. Run npm run check:protocol-revision. If it fails, update package.json with the expected devtools-protocol version.
5. Run npm run build and npm install.
6. Run npm run test and ensure that all tests pass. If a test fails, bisect the upstream cause of the failure, and either update the test expectations accordingly (if it was an intended change) or work around the changes in Puppeteer (if it’s not desirable to change Puppeteer’s observable behavior).
7. Commit and push your changes and open a pull request. The commit message must contain the version in Chromium <version> (<revision>) format to ensure that pptr.dev can parse it correctly, e.g. 'feat(chromium): roll to Chromium 90.0.4427.0 (r856583)'.

Bisecting upstream changes

Sometimes, performing a Chromium roll causes tests to fail. To figure out the cause, you need to bisect Chromium revisions to figure out the earliest possible revision that changed the behavior. The script in utils/bisect.js can be helpful here. Given a pattern for one or more unit tests, it will automatically bisect the current range:

node utils/bisect.js --good 686378 --bad 706915 script.js

node utils/bisect.js --unit-test Response.fromCache

By default, it will use the Chromium revision in src/revisions.ts from the main branch and from the working tree to determine the range to bisect.

Releasing to npm

We use release-please to automate releases. When a release should be done, check for the release PR in our pull requests and merge it.