Contributing

Adding a new plugin to support (when approved in the next ECMAScript version)

Update plugin-features.js

Example:

If you were going to add ** which is in ES2016:

Find the relevant entries on compat-table:

exponentiation (**) operator

Find the corresponding babel plugin:

transform-exponentiation-operator

And add them in this structure:

// es2016
"transform-exponentiation-operator": {
  features: [
    "exponentiation (**) operator",
  ],
},

Update built-in-features.js

Example:

In case you want to add Object.values which is in ES2017:

Find the relevant feature and subfeature on compat-table and split it with /:

Object static methods / Object.values

Find the corresponding module on core-js:

es7.object.values.js

Find required ES version in built-in-features.js and add the new feature:

const es2017 = {
  //...
  "es7.object.values": "Object static methods / Object.values"
}

Update plugins.json

Until compat-table is a standalone npm module for data we are using the git url

"compat-table": "kangax/compat-table#[latest-commit-hash]",

So we update and then run npm run build-data. If there are no changes, then plugins.json will be the same.

Tests

Running tests locally

npm test

Checking code coverage locally

npm run coverage

Writing tests

General

All the tests for babel-preset-env exist in the test/fixtures folder. The test setup and conventions are exactly the same as testing a Babel plugin, so please read our documentation on writing tests.

Testing the debug option

Testing debug output to stdout is similar. Under the test/debug-fixtures, create a folder with a descriptive name of your test, and add the following:

• Add a options.json file (just as the other tests, this is essentially a .babelrc) with the desired test configuration (required)
• Add a stdout.txt file with the expected debug output. For added convenience, if there is no stdout.txt present, the test runner will generate one for you.