CONTRIBUTING.md

Contributing

Contributions are always welcome. If you don't know how you can help, you can check issues or ask @zloirock.

How to add a new polyfill

• The polyfill implementation should be added to the packages/core-js/modules directory.
• Any shared helpers should be added to the packages/core-js/internals directory.
• If the implementation for the pure version differs from the global version, add it to packages/core-js-pure/override directory. The rest parts of core-js-pure will be copied from core-js package.
• For export the polyfill, in almost all cases use internals/export helper.
• Add feature detection of the polyfill to tests/compat/tests.js and compatibility data to packages/core-js-compat/src/data.mjs and packages/core-js-compat/src/modules-by-versions.mjs (this data also used for getting the default list of polyfills at bundling).
• Add it to entry points where it's required: directories packages/core-js/features, packages/core-js/es, packages/core-js/proposals, packages/core-js/stage and packages/core-js/web.
• Add unit tests to tests/tests and tests/pure.
• Add tests of entry points to tests/commonjs.js.
• Add documentation to README.md.

Style and standards

The coding style should follow our .eslintrc. You can test it by calling npm run lint. Different places have different syntax and standard library limitations:

• Polyfill implementations should use only ES3 syntax and standard library. Polyfills should not use another polyfill from the global namespace.
• In unit tests should be used modern syntax with our minimalistic Babel config. Unit tests for the pure version should not use any modern standard library features.
• In building tools and tests, performed in Node.js, should be used only available in Node.js 4 syntax and standard library.

File names should be in the kebab-case. Name of files with polyfills should follow naming convention namespace.subnamespase-where-required.feature-name, for example, esnext.promise.try. Top-level namespace could be es for stable ECMAScript features, esnext for ECMAScript proposals and web for other web standards.

Testing

Before testing, you should install dependencies:

$ npm i

You can run all tests by

$ npm run test

You can run parts of the test case separately:

• Linting:

$ npm run lint

• Global version unit tests:

$ npm run test-unit-global-standalone

• pure version unit tests:

$ npm run test-unit-pure-standalone

• Promises/A+ test case:

$ npm run test-promises-standalone

• ECMAScript Observable test case:

$ npm run test-observables-standalone

• CommonJS entry points tests:

$ npm run test-entries-standalone

If you want to run tests in a certain browser at first you should build packages and test bundles:

$ npm run build

• For running the global version of the unit test case use this file:

tests/tests.html

• For running the pure version of the unit test case use this file:

tests/pure.html

Updating core-js-compat data

For updating core-js-compat data:

• Clone core-js repo.
• If you wanna add new data for a browser, run in this browser tests/compat/index.html and you will see which core-js modules required for this browser.
• If you wanna add new data for Node.js, run tests/compat/node-runner.js in required Node.js version and you will see results in the console.
• After getting this data, add it to packages/core-js-compat/src/data.mjs.
• If you wanna add new mapping (for example, add a new iOS Safari version based on Safari or Node.js based on Chrome), add it to packages/core-js-compat/src/mapping.mjs.
• Add a pull request to core-js repo.