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- # Contributing
- ## Adding a new plugin to support (when approved in the next ECMAScript version)
- ### Update [`plugin-features.js`](https://github.com/babel/babel-preset-env/blob/master/data/plugin-features.js)
- *Example:*
- If you were going to add `**` which is in ES2016:
- Find the relevant entries on [compat-table](https://kangax.github.io/compat-table/es2016plus/#test-exponentiation_(**)_operator):
- `exponentiation (**) operator`
- Find the corresponding babel plugin:
- `transform-exponentiation-operator`
- And add them in this structure:
- ```js
- // es2016
- "transform-exponentiation-operator": {
- features: [
- "exponentiation (**) operator",
- ],
- },
- ```
- ### Update [`built-in-features.js`](https://github.com/babel/babel-preset-env/blob/master/data/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](https://kangax.github.io/compat-table/es2016plus/#test-Object_static_methods_Object.values)
- and split it with `/`:
- `Object static methods / Object.values`
- Find the corresponding module on [core-js](https://github.com/zloirock/core-js/tree/master/modules):
- `es7.object.values.js`
- Find required ES version in [`built-in-features.js`](https://github.com/babel/babel-preset-env/blob/master/data/built-in-features.js) and add the new feature:
- ```js
- const es2017 = {
- //...
- "es7.object.values": "Object static methods / Object.values"
- }
- ```
- ### Update [`plugins.json`](https://github.com/babel/babel-preset-env/blob/master/data/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
- ```bash
- npm test
- ```
- ### Checking code coverage locally
- ```bash
- 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](https://github.com/babel/babel/blob/master/CONTRIBUTING.md#babel-plugin-x).
- #### 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.
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