babel-plugin-resolve-barrel-files

babel-plugin-resolve-barrel-files

This plugin parses and resolves a barrel file

What is a barrel file?

Usually, index files with a lot of export statements, more info here

But really, what it does?

Given a module that export its dependencies using a barrel file like this:

// my-lib/index.js
export { map } from './dist/map';
export { chain } from './dist/chain';
export { filter } from './dist/filter';
export { groupBy } from './dist/groupBy';

And that you import it like this:

import { map, chain } from 'my-lib';

it will transform your code to:

import { map } from 'my-lib/dist/map';
import { chain } from 'my-lib/dist/chain';

Since a barrel file exports all files from a lib, babel/bundlers usually will import and parse all of those files because they can have side effects.

This plugin will drop unused imports from barrel files at lib roots, which will also remove import side effects.

This probably can help you to reduce the bundle size and help your bundler to be faster.

Why? babel isn't a bundler, why resolve in babel?

Because React Native sucks (or I suck because I don't know how to do this in metro).

Not supported

Full imports

Right now, this plugin doesn't support full imports like:

import all from 'my-lib'

We could ignore this, in the future and just warn that this kind of import make this plugin useless.

Barrel effects and local exports

Since this plugin is meant to make the barrel file 'invisible' to the bundler, it will not resolve local exports.

a barrel file like this:

export default "foo";

if (!x) {
  throw Error("foo")
}

Will do nothing

CommonJS dynamic stuff

CommonJS is supported, although a lot of corner cases are not supported because I wrote myself the code to find and track exports. (PR welcome, would love to improve the CJS support)

Usually, a babel generated CommonJS will work fine.

Installation

npm install --save babel-plugin-resolve-barrel-files
# or
yarn add -D babel-plugin-resolve-barrel-files

Usage

Declare it in your babel config file:

const path = require('path');

module.exports = {
  // ...,
  plugins: [
    [
      'resolve-barrel-files',
      {
        'my-lib': {
          moduleType: 'commonjs', // or 'esm'
          barrelFilePath: require.resolve('my-lib')
          // if you want to debug this plugin
          // logLevel: "debug" | "info" 
        },
      },
    ]
  ]
}

Note: if you make changes to the babel config be sure to restart your bundler with a clear babel cache

I have a problem, what should I do?

Feel free to open a PR or an issue and I'll try to help you :D

Mentions

Heavily inspired by babel-plugin-transform-imports