babel-jest/README.md

Jest plugin to use babel for transformation.

# babel-jest

[Babel](https://github.com/babel/babel) [jest](https://github.com/jestjs/jest) plugin

## Usage

If you are already using `jest-cli`, add `babel-jest` and it will automatically compile JavaScript code using Babel.

```bash
yarn add --dev babel-jest @babel/core
```

If you would like to write your own preprocessor, uninstall and delete babel-jest and set the [config.transform](https://jestjs.io/docs/configuration#transform-object-string-string) option to your preprocessor.

## Setup

_Note: this step is only required if you are using `babel-jest` with additional code preprocessors._

To explicitly define `babel-jest` as a transformer for your JavaScript code, map _.js_ files to the `babel-jest` module. Typescript files are also supported.

By default, it loads your existing Babel configuration (if any)

```json
"transform": {
  "\\.[jt]sx?$": "babel-jest"
},
```

You can also pass further [babel options](https://babeljs.io/docs/options)

```json
"transform": {
  "\\.[jt]sx?$": ["babel-jest", { "extends": "./babel.config.js", "plugins": ["babel-plugin-transform-import-meta"] }]
},
```

By default, `babel-jest` includes `babel-preset-jest`. In addition to the babel options, we introduce a new option, `excludeJestPreset`, which allows you to disable this behavior. Note that this will break `jest.mock` hoisting.

```json
"transform": {
  "\\.[jt]sx?$": ["babel-jest", { "excludeJestPreset": true }],
}
```