puppeteer/CONTRIBUTING.md

• How to Contribute
  • Contributor License Agreement
  • Getting Code
  • Code reviews
  • Code Style
  • TypeScript guidelines
  • API guidelines
  • Commit Messages
  • Writing Documentation
  • Adding New Dependencies
  • Running & Writing Tests
  • Public API Coverage
  • Debugging Puppeteer
• For Project Maintainers
  • Releasing to npm
  • Updating npm dist tags

How to Contribute

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. Run Puppeteer tests locally. For more information about tests, read Running & Writing Tests.

npm run unit

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.
• We are migrating the Puppeteer codebase to TypeScript which is why you'll find both JS and TS files in src/.
• 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 eslint

You can check your code (both JS & TS) type-checks by running:

npm run tsc

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.

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 Semantic Commit Messages format:

label(namespace): title

description

footer

1. label is one of the following:
   • fix - puppeteer bug fixes.
   • feat - puppeteer features.
   • docs - changes to docs, e.g. docs(api.md): .. to change documentation.
   • test - changes to puppeteer tests infrastructure.
   • style - puppeteer code style: spaces/alignment/wrapping etc.
   • chore - build-related work, e.g. doclint changes / travis / appveyor.
2. namespace is put in parenthesis after label and is optional. Must be lowercase.
3. title is a brief summary of changes.
4. description is optional, new-line separated from title and is in present tense.
5. footer is optional, new-line separated from description and contains "fixes" / "references" attribution to github issues.
6. footer should also include "BREAKING CHANGE" if current API clients will break due to this change. It should explain what changed and how to get the old behavior.

Example:

fix(page): fix page.pizza method

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

Fixes #123, Fixes #234

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

Writing Documentation

All public API should have a descriptive entry in docs/api.md. There's a documentation linter which makes sure documentation is aligned with the codebase.

To run the documentation linter, use:

npm run doc

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.

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 (test 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 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 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 unit

• To run tests with custom browser executable:

BINARY=<path-to-executable> npm run 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

Releasing to npm

Releasing to npm consists of the following phases:

1. Source Code: mark a release.
   1. Bump package.json version following the SEMVER rules.
   2. Run npm run doc to update the docs accordingly.
   3. Update the “Releases per Chromium Version” list in docs/api.md to include the new version.
   4. Send a PR titled 'chore: mark version vXXX.YYY.ZZZ' (example).
   5. Make sure the PR passes all checks.
      • WHY: there are linters in place that help to avoid unnecessary errors, e.g. like this
   6. Merge the PR.
   7. Once merged, publish the release notes using GitHub's “draft new release tag” option.
      • NOTE: tag names are prefixed with 'v', e.g. for version 1.4.0 the tag is v1.4.0.
      • For the “raw notes” section, use git log --pretty="%h - %s" v2.0.0..HEAD.
2. Publish puppeteer to npm.
   1. On your local machine, pull from upstream and make sure the last commit is the one just merged.
   2. Run git status and make sure there are no untracked files.
      • WHY: this is to avoid adding unnecessary files to the npm package.
   3. Run npx pkgfiles to make sure you don't publish anything unnecessary.
   4. Run npm publish. This publishes the puppeteer package.
3. Publish puppeteer-core to npm.
   1. Run ./utils/prepare_puppeteer_core.js. The script changes the name inside package.json to puppeteer-core.
   2. Run npm publish. This publishes the puppeteer-core package.
   3. Run git reset --hard to reset the changes to package.json.
4. Source Code: mark post-release.
   1. Bump package.json version to -post version, run npm run doc to update the “released APIs” section at the top of docs/api.md accordingly, and send a PR titled 'chore: bump version to vXXX.YYY.ZZZ-post' (example)
      • NOTE: no other commits should be landed in-between release commit and bump commit.

Updating npm dist tags

For both puppeteer and puppeteer-core we maintain chrome-* npm dist tags, e.g. chrome-75 and so on. These tags match the Puppeteer version that corresponds to the chrome-* release.

These tags are updated on every Puppeteer release.

Managing tags 101:

# List tags
$ npm dist-tag ls puppeteer
# Add tags
$ npm dist-tag add puppeteer@3.0.0 chrome-81
$ npm dist-tag add puppeteer-core@3.0.0 chrome-81