Edit

.babelrc

Lookup behavior

Babel will look for a .babelrc in the current directory (which defaults to cwd). For example if you are using a monorepo and you run Babel from the packageA:

project
├── .babelrc // ignored
└── monorepo
    └── packageA
        ├── package.json
        └── ...

Use "babelrc": false in options to stop lookup behavior, or provide the --no-babelrc CLI flag.

Merging behavior

If Babel finds other .babelrc files while transpiling files in subfolder, it will merge the configuration together.

Note that it can lead to undefined behaviors, and we recommend to use babel.config.js documentation instead.

"overrides"

Babel takes this idea from ESLint. This gives you the ability to apply a configuration to specific files.

Every config object can specify a test/include/exclude (like Webpack). Each item allows an item, or array of items that can be a string, RegExp, or function.

"overrides" is an array of sub-configs that apply on top of the base configs that will apply based on their test/include/exclude values.

Example of compiling client code against browsers while the rest of the server code is compiled against node.

{
  "presets": [
    ["env", { 
      "targets": { "node": "current" },
    }],
  ],
  "overrides": [{
    "test": "./client",
    "presets": [
      ["env", { 
        "targets": { "browsers": ["last 2 versions"] },
      }],
    ],
  }],
}

env (environment) option

You can use the env option to set specific options when in a certain environment:

{
  "env": {
    "production": {
      "plugins": ["@babel/plugin-transform-classes"]
    }
  }
}

Options specific to a certain environment are merged into and overwrite non-env specific options.

The env key will be taken from process.env.BABEL_ENV, when this is not available then it uses process.env.NODE_ENV if even that is not available then it defaults to "development".

envName

Instead of setting an environment variable, one can pass envName or --env-name explicitly.

Setting an environment variable

Or you can set this environment variable implicitly with the following:

Unix

At the start of a command:

BABEL_ENV=production YOUR_COMMAND_HERE

Or as a separate command:

export BABEL_ENV=production

YOUR_COMMAND_HERE

Windows

SET BABEL_ENV=production

YOUR_COMMAND_HERE

If you want your command to work across platforms, you can use cross-env