rollup-plugin-esm-import-to-url

Rollup plugin to transform "bare" import specifiers to absolute URLs in ES modules

Installation

$ npm install rollup-plugin-esm-import-to-url

Usage

import esmImportToUrl from 'rollup-plugin-esm-import-to-url';
 
export default {
    input: 'source/main.js',
    plugins: [esmImportToUrl({
        imports: {
            'some-library': 'http://cdn.com/some-library/v1',
        },
    })],
    output: {
        file: 'build.js',
        format: 'esm'
    }
};

Description

This plugin transforms "bare" import specifiers to absolute URL specifiers in ES modules. The module refered to by the "bare" import specifier will be treated as an external and its source will not be included in the bundle but refered to by the URL.

In our source:

import { LitElement, html, css } from 'lit-element';

In our Rollup config, we map lit-element to a bundle on a CDN:

export default {
    input: 'source/main.js',
    plugins: [esmImportToUrl({
        imports: {
            'lit-element': 'https://cdn.pika.dev/lit-element/v2',
        },
    })],
    output: {
        file: 'build.js',
        format: 'esm'
    }
};

Our output bundle will then be:

import { LitElement, html, css } from 'https://cdn.pika.dev/lit-element/v2';

Options

This plugin takes an import map as options:

option	default	type	required	details
imports	{}	object	false	Mapping between "bare" import specifiers and absolute URLs.

This module will only care about "bare" import specifiers which maps to absolute URLs in the import map. Any other import specifiers defined in the import map will be ignored.

Note on externals

The imports defined for imports to this module must not occure in the Rollup external option. If so, this module will throw.

In other words, this will not work:

export default {
    input: 'source/main.js',
    external: ['lit-element'],
    plugins: [esmImportToUrl({
        imports: {
            'lit-element': 'https://cdn.pika.dev/lit-element/v2',
        },
    })],
    output: {
        file: 'build.js',
        format: 'esm'
    }
};

ESM only

This module will only work when the output are ES modules.

License

Copyright (c) 2019 Trygve Lie

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.