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95 lines
3.6 KiB
95 lines
3.6 KiB
1 month ago
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# Contributing
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## Adding a new plugin or polyfill to support (when approved in the next ECMAScript version)
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### Update [`plugin-features.js`](https://github.com/babel/babel/blob/main/packages/babel-compat-data/scripts/data/plugin-features.js)
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*Example:*
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If you were going to add `**` which is in ES2016:
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Find the relevant entries on [compat-table](https://kangax.github.io/compat-table/es2016plus/#test-exponentiation_(**)_operator):
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`exponentiation (**) operator`
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Find the corresponding babel plugin:
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`@babel/plugin-transform-exponentiation-operator`
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And add them in this structure:
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```js
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// es2016
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"@babel/plugin-transform-exponentiation-operator": {
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features: [
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"exponentiation (**) operator",
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],
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},
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```
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### Update data for `core-js@2` polyfilling
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*Example:*
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In case you want to add `Object.values` which is in ES2017:
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Find the relevant feature and subfeature on [compat-table](https://kangax.github.io/compat-table/es2016plus/#test-Object_static_methods_Object.values)
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and split it with `/`:
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`Object static methods / Object.values`
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Find the corresponding module on [`core-js@2`](https://github.com/zloirock/core-js/tree/v2/modules):
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`es7.object.values.js`
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Find required ES version in [`corejs2-built-in-features.js`](https://github.com/babel/babel/blob/main/packages/babel-preset-env/data/corejs2-built-in-features.js) and add the new feature:
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```js
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const es = {
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//...
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"es7.object.values": "Object static methods / Object.values"
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}
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```
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If you want to transform a new built-in by `useBuiltIns: 'usage'`, add mapping to related `core-js` modules to [this file](https://github.com/babel/babel/blob/main/packages/babel-preset-env/polyfills/corejs2/built-in-definitions.js).
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### Update data for `core-js@3` polyfilling
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Just update the version of [`core-js-compat`](https://github.com/zloirock/core-js/tree/main/packages/core-js-compat) in dependencies.
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If you want to transform a new built-in by `useBuiltIns: 'usage'`, add mapping to related [`core-js`](https://github.com/zloirock/core-js/tree/main/packages/core-js/modules) modules to [this file](https://github.com/babel/babel/blob/main/packages/babel-preset-env/polyfills/corejs3/built-in-definitions.js).
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If you want to mark a new proposal as shipped, add it to [this list](https://github.com/babel/babel/blob/main/packages/babel-preset-env/polyfills/corejs3/shipped-proposals.js).
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### Update [`plugins.json`](https://github.com/babel/babel/blob/main/packages/babel-preset-env/data/plugins.json)
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Until `compat-table` is a standalone npm module for data we are using the git commit in `packages/babel-compat-data/scripts/download-compat-table.sh`
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`COMPAT_TABLE_COMMIT=[latest-commit-hash]`,
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So we update and then run `npm run build-data`. If there are no changes, then `plugins.json` will be the same.
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## Tests
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### Running tests
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See general [CONTRIBUTING.md](https://github.com/babel/babel/blob/main/CONTRIBUTING.md#running-lintingtests).
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### Writing tests
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#### General
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All the tests for `@babel/preset-env` exist in the `test/fixtures` folder. The
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test setup and conventions are exactly the same as testing a Babel plugin, so
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please read our [documentation on writing tests](https://github.com/babel/babel/blob/main/CONTRIBUTING.md#babel-plugin-x).
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#### Testing the `debug` option
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Testing debug output to `stdout` is similar. Under the `test/debug-fixtures`,
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create a folder with a descriptive name of your test, and add the following:
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* Add a `options.json` file (just as the other tests, this is essentially a
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`.babelrc`) with the desired test configuration (required)
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* Add a `stdout.txt` file with the expected debug output. For added
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convenience, if there is no `stdout.txt` present, the test runner will
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generate one for you.
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