@rollup/plugin-legacy

@rollup/plugin-legacy

🍣 A Rollup plugin which adds export declarations to legacy non-module scripts.

Requirements

This plugin requires an LTS Node version (v14.0.0+) and Rollup v1.20.0+.

Install

Using npm:

npm install @rollup/plugin-legacy --save-dev

Usage

Create a rollup.config.js configuration file and import the plugin:

import legacy from '@rollup/plugin-legacy';

export default {
  entry: 'src/main.js',
  output: {
    dir: 'output',
    format: 'cjs'
  },
  plugins: [legacy({ 'vendor/some-library.js': 'someLibrary' })]
};

Then call rollup either via the CLI or the API.

Options

Type: Object
Default: null

Specifies an Object which defines exports used when importing corresponding scripts. The Object allows specifying script paths as a key, and the corresponding value as the exports for that script. For example:

Object Format

The Object format allows specifying aliases as a key, and the corresponding value as the actual import value. For example:

legacy({
  'vendor/some-library.js': 'someLibrary',

  'vendor/another-library.js': {
    foo: 'anotherLib.foo',
    bar: 'anotherLib.bar',
    baz: 'anotherLib.baz'
  }
});

The configuration above will create a default export when importing 'vendor/some-library.js' that corresponds with the someLibrary variable that it creates. It will also create named exports when importing 'vendor/another-library.js'.

Motivation

Occasionally you'll find a useful snippet of code from the Old Days, before newfangled technology like npm. These scripts will typically expose themselves as var someLibrary = ... or window.someLibrary = ..., the expectation being that other scripts will grab a reference to the library from the global namespace.

It's usually easy enough to convert these to modules. But why bother? You can just add the legacy plugin, configure it accordingly, and it will be turned into a module automatically. With the example config below, the following code...

// vendor/some-library.js
var someLibrary = {
  square: function (n) {
    return n * n;
  },
  cube: function (n) {
    return n * n * n;
  }
};

...will have a default export appended to it, allowing other modules to access it:

export default someLibrary;

It can also handle named exports. Using the same config, this...

// vendor/another-library.js
var anotherLibrary = {
  foo: ...,
  bar: ...,
  baz: ...
};

...will get the following appended:

var __export0 = anotherLibrary.foo;
export { __export0 as foo };
var __export0 = anotherLibrary.bar;
export { __export0 as bar };
var __export0 = anotherLibrary.baz;
export { __export0 as baz };

Meta

CONTRIBUTING

LICENSE (MIT)