timburgess / rollup-plugin-import-map

Create an import map from Rollup entry points

Rollup Import Map Plugin

This Rollup plugin generates an import map for all your entry points to their hashed filename. It's designed to work with filenames in the format of [name]-[hash].js.

If you're serving html via a traditional backend, the backend will likely use html templates that have script elements that reference the .js bundle(s).

Rollup can build assets with a hash suffix e.g. base-4KxXYrTd.js to prevent cache issues when new JS bundles are served. As browsers now support import maps, this plugin can generate an import-map.json file. The backend can then incorporate the import map into the html template. On page load, the browser will use the import map to load base-4KxXYrTd.js for the base.js file.

See https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script/type/importmap for the MDN Import Map reference.

Installation

Using npm:

npm install --save-dev TODO

Usage

Add the plugin to your rollup.config.js:

import importMap from 'rollup-plugin-import-map'

export default {
  input: {
    // your entry points here
  },
  output: {
    dir: 'dist',
    format: 'esm',
    entryFileNames: '[name]-[hash].js',
  },
  plugins: [importMap()]
}

With the import-map.json now being created, add a <script type="importmap" src="import-map.json"></script> to the html template.