babel-loader

This package allows transpiling JavaScript files using Babel and webpack.

Notes: Issues with the output should be reported on the babel issue tracker.

Install

webpack 3.x | babel-loader 8.x | babel 7.x

npm install "babel-loader@^8.0.0-beta" @babel/core @babel/preset-env webpack

webpack 3.x babel-loader 7.x | babel 6.x

npm install babel-loader babel-core babel-preset-env webpack

Usage

Documentation: Using loaders

Within your webpack configuration object, you'll need to add the babel-loader to the list of modules, like so:

module: {
  rules: [
    {
      test: /\.js$/,
      exclude: /(node_modules|bower_components)/,
      use: {
        loader: 'babel-loader',
        options: {
          presets: ['@babel/preset-env']
        }
      }
    }
  ]
}

##

See the babel options.

You can pass options to the loader by using the options property:

module: {
  rules: [
    {
      test: /\.js$/,
      exclude: /(node_modules|bower_components)/,
      use: {
        loader: 'babel-loader',
        options: {
          presets: ['@babel/preset-env'],
          plugins: [require('@babel/plugin-proposal-object-rest-spread')]
        }
      }
    }
  ]
}

This loader also supports the following loader-specific option:

• cacheDirectory: Default false. When set, the given directory will be used to cache the results of the loader. Future webpack builds will attempt to read from the cache to avoid needing to run the potentially expensive Babel recompilation process on each run. If the value is blank (loader: 'babel-loader?cacheDirectory') or true (loader: babel-loader?cacheDirectory=true) the loader will use the default cache directory in node_modules/.cache/babel-loader or fallback to the default OS temporary file directory if no node_modules folder could be found in any root directory.

• cacheIdentifier: Default is a string composed by the babel-core's version, the babel-loader's version, the contents of .babelrc file if it exists and the value of the environment variable BABEL_ENV with a fallback to the NODE_ENV environment variable. This can be set to a custom value to force cache busting if the identifier changes.

• babelrc: Default true. When false, no options from .babelrc files will be used; only the options passed to babel-loader will be used.

Note: The sourceMap option is ignored, instead sourceMaps are automatically enabled when webpack is configured to use them (via the devtool config option).

Troubleshooting

babel-loader is slow!

Make sure you are transforming as few files as possible. Because you are probably matching /\.js$/, you might be transforming the node_modules folder or other unwanted source.

To exclude node_modules, see the exclude option in the loaders config as documented above.

You can also speed up babel-loader by as much as 2x by using the cacheDirectory option. This will cache transformations to the filesystem.

babel is injecting helpers into each file and bloating my code!

babel uses very small helpers for common functions such as _extend. By default this will be added to every file that requires it.

You can instead require the babel runtime as a separate module to avoid the duplication.

The following configuration disables automatic per-file runtime injection in babel, instead requiring babel-plugin-transform-runtime and making all helper references use it.

See the docs for more information.

NOTE: You must run npm install @babel/plugin-transform-runtime --save-dev to include this in your project and babel-runtime itself as a dependency with npm install @babel/runtime --save.

rules: [
  // the 'transform-runtime' plugin tells babel to require the runtime
  // instead of inlining it.
  {
    test: /\.js$/,
    exclude: /(node_modules|bower_components)/,
    use: {
      loader: 'babel-loader',
      options: {
        presets: ['@babel/preset-env'],
        plugins: ['@babel/plugin-transform-runtime']
      }
    }
  }
]

NOTE: transform-runtime & custom polyfills (e.g. Promise library)

Since babel-plugin-transform-runtime includes a polyfill that includes a custom regenerator runtime and core.js, the following usual shimming method using webpack.ProvidePlugin will not work:

// ...
        new webpack.ProvidePlugin({
            'Promise': 'bluebird'
        }),
// ...

The following approach will not work either:

require('@babel/runtime/core-js/promise').default = require('bluebird');

var promise = new Promise;

which outputs to (using runtime):

'use strict';

var _Promise = require('@babel/runtime/core-js/promise')['default'];

require('@babel/runtime/core-js/promise')['default'] = require('bluebird');

var promise = new _Promise();

The previous Promise library is referenced and used before it is overridden.

One approach is to have a "bootstrap" step in your application that would first override the default globals before your application:

// bootstrap.js

require('@babel/runtime/core-js/promise').default = require('bluebird');

// ...

require('./app');

The node API for babel has been moved to babel-core.

If you receive this message it means that you have the npm package babel installed and use the short notation of the loader in the webpack config (which is not valid anymore as of webpack 2.x):

  {
    test: /\.js$/,
    loader: 'babel',
  }

Webpack then tries to load the babel package instead of the babel-loader.

To fix this you should uninstall the npm package babel as it is deprecated in babel v6. (instead install babel-cli or babel-core) In the case one of your dependencies is installing babel and you cannot uninstall it yourself, use the complete name of the loader in the webpack config:

  {
    test: /\.js$/,
    loader: 'babel-loader',
  }

Customized Loader

babel-loader exposes a loader-builder utility that allows users to add custom handling of Babel's configuration for each file that it processes.

.custom accepts a callback that will be called with the loader's instance of babel so that tooling can ensure that it using exactly the same @babel/core instance as the loader itself.

Example

module.exports = require("babel-loader").custom(babel => {
  function myPlugin() {
    return {
      visitor: {},
    };
  }

  return {
    // Passed the loader options.
    customOptions({ opt1, opt2, ...loader }) {
      return {
        // Pull out any custom options that the loader might have.
        custom: { opt1, opt2 },

        // Pass the options back with the two custom options removed.
        loader,
      };
    },

    // Passed Babel's 'PartialConfig' object. 
    config(cfg) {
      if (cfg.hasFilesystemConfig()) {
        // Use the normal config
        return cfg.options;
      }

      return {
        ...cfg.options,
        plugins: [
          ...(cfg.options.plugins || []),

          // Include a custom plugin in the options.
          myPlugin,
        ],
      };
    },

    result(result) {
      return {
        ...result,
        code: result.code + "\n// Generated by some custom loader",
      };
    },
  };
});

customOptions(options: Object): { custom: Object, loader: Object }

Given the loader's options, split custom options out of babel-loader's options.

config(cfg: PartialConfig): Object

Given Babel's PartialConfig object, return the options object that should be passed to babel.transform.

result(result: Result): Result

Given Babel's result object, allow loaders to make additional tweaks to it.

License License" class="icon-link" href="#license">