rollup-plugin-babel

Seamless integration between Rollup and Babel.

Why?

If you're using Babel to transpile your ES6/7 code and Rollup to generate a standalone bundle, you have a couple of options:

• run the code through Babel first, being careful to exclude the module transformer, or
• run the code through Rollup first, and then pass it to Babel.

Both approaches have disadvantages – in the first case, on top of the additional configuration complexity, you may end up with Babel's helpers (like classCallCheck) repeated throughout your code (once for each module where the helpers are used). In the second case, transpiling is likely to be slower, because transpiling a large bundle is much more work for Babel than transpiling a set of small files.

Either way, you have to worry about a place to put the intermediate files, and getting sourcemaps to behave becomes a royal pain.

Using Rollup with rollup-plugin-babel makes the process far easier.

Installation

npm install --save-dev rollup-plugin-babel

Usage

import { rollup } from 'rollup';
import babel from 'rollup-plugin-babel';

rollup({
  entry: 'main.js',
  plugins: [
    babel({
      exclude: 'node_modules/**'
    })
  ]
}).then(...)

All options are as per the Babel documentation, except options.include and options.exclude (each a minimatch pattern, or array of minimatch patterns), which determine which files are transpiled by Babel (by default, all files are transpiled).

Babel will respect .babelrc files – this is generally the best place to put your configuration.

Configuring Babel

The following applies to Babel 6 only. If you're using Babel 5, do npm i -D rollup-plugin-babel@1, as version 2 and above no longer supports Babel 5

tl;dr: use the es2015-rollup preset instead of es2015.

npm install --save-dev babel-preset-es2015-rollup

// .babelrc
{
  "presets": [ "es2015-rollup" ]
}

Modules

The es2015 preset includes the transform-es2015-modules-commonjs plugin, which converts ES6 modules to CommonJS – preventing Rollup from working. Instead, you should either use the es2015-rollup preset, which excludes that plugin, or otherwise ensure that the modules-commonjs plugin is excluded. Rollup will throw an error if this is incorrectly configured.

Helpers

In some cases Babel uses helpers to avoid repeating chunks of code – for example, if you use the class keyword, it will use a classCallCheck function to ensure that the class is instantiated correctly.

By default, those helpers will be inserted at the top of the file being transformed, which can lead to duplication. It's therefore recommended that you use the external-helpers plugin, which is automatically included in the es2015-rollup preset. Rollup will combine the helpers in a single block at the top of your bundle.

Alternatively, if you know what you're doing, you can use the transform-runtime plugin. If you do this, use runtimeHelpers: true:

rollup.rollup({
  ...,
  plugins: [
    babel({ runtimeHelpers: true })
  ]
}).then(...)

License

MIT