puppeteer/CONTRIBUTING.md

# 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.

## Code reviews

All submissions, including submissions by project members, require review. We
use GitHub pull requests for this purpose. Consult
[GitHub Help](https://help.github.com/articles/about-pull-requests/) for more
information on using pull requests.

## Code Style

- coding style is fully defined in [.eslintrc](https://github.com/GoogleChrome/puppeteer/blob/master/.eslintrc.js). Please make sure to run `npm run lint` before submitting PR
- code should be annotated with [closure annotations](https://github.com/google/closure-compiler/wiki/Annotating-JavaScript-for-the-Closure-Compiler)
- comments should be generally avoided. If the code would not be understood without comments, consider re-writing the code to make it self-explanatory

## Documentation

All public API should have a descriptive entry in the [docs/api.md](https://github.com/GoogleChrome/puppeteer/blob/master/docs/api.md). There's a [documentation linter](https://github.com/GoogleChrome/puppeteer/tree/master/utils/doclint) that:
- makes sure documentation is aligned with the codebase
- generates up-to-date table-of-contents

To run the linter, use
```
npm run doc
```

## Dependencies

For all dependencies (both installation and development):
- **Do not add** a dependency if the desired functionality is easily implementable in scope of the project
- if adding a dependency, it should be well-maintained and trustworthy

For installation dependencies:
- **do not add** installation dependency unless it's critical to project success

## Tests

- every feature should be accompanied by a test
- every public api event/method should be accompanied by a test
- tests should be *hermetic*. They should not require internet connection or 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 [test/test.js](https://github.com/GoogleChrome/puppeteer/blob/master/test/test.js)
and are written using [Jasmine](https://jasmine.github.io/) testing framework.

- To run all tests:
```
npm run unit
```
- To filter tests by name:
```
npm run unit -- --filter=waitFor
```
- To run a specific test, substitute the `it` with `fit` (mnemonic rule: '*focus it*'):
```js
  ...
  // Using "fit" to run specific test
  fit('should work', SX(function() {
    await response = page.navigate(EMPTY_PAGE);
    expect(response.ok).toBe(true);
  }))
```
- To run tests in non-headless mode:
```
HEADLESS=false npm run unit
```
- To debug a test, "focus" a test first and then run
```
npm run debug-unit
```

There are also phantomjs tests located under [third_party/phantomjs/test](https://github.com/GoogleChrome/puppeteer/tree/master/third_party/phantomjs). These
are used to test `phantom_shim`.

## Public API Coverage

Every public API method should be called at least once during `npm run unit` command.
To ensure this, there's a `npm run coverage` command which tracks public API usage and reports back if some methods were not called.

## Debugging
Puppeteer uses [DEBUG](https://github.com/visionmedia/debug) module to expose some of it's inner guts under the `puppeteer` namespace.
Try putting the following script in the `script.js` and running it via `DEBUG=* node script.js`:

```js
const {Browser} = require('puppeteer');
const browser = new Browser();
browser.newPage().then(async page => {
  await page.navigate('https://example.com');
  browser.close();
});
```

Tips-n-tricks:
- `DEBUG=*,-*:protocol node script.js` - dump everything BUT protocol messages
- `DEBUG=*:page node script.js` - dump only Page's API calls
- `DEBUG=*:mouse,*:keyboard node script.js` - dump only Mouse and Keyboard API calls