rollup-plugin-import-map

Plugin to rewrite bare imports to URLs as defined in import maps

Rollup Eik plugin to support the use of import maps to map "bare" import specifiers in ES modules.

Installation

$ npm install @eik/rollup-plugin-import-map

Usage

import eikImportMapPlugin from "@eik/rollup-plugin-import-map";

export default {
  input: "source/main.js",
  plugins: [eikImportMapPlugin()],
  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 external and its source will not be included in the bundle but refered to by URL.

The plugin will attempt to read import map URLs from eik.json if present.

export default {
  input: "source/main.js",
  plugins: [eikImportMapPlugin()],
  output: {
    file: "build.js",
    format: "esm",
  },
};

The path to the location of an eik.json file can be specified with the path option.

export default {
  input: "source/main.js",
  plugins: [eikImportMapPlugin({ path: "/path/to/eik-json-folder" })],
  output: {
    file: "build.js",
    format: "esm",
  },
};

The plugin can also be told which URLs to load import maps from directly using the urls option.

export default {
  input: "source/main.js",
  plugins: [eikImportMapPlugin({ urls: `http://myserver/import-map` })],
  output: {
    file: "build.js",
    format: "esm",
  },
};

Additionally, individual mappings can be specified using the maps option.

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

If several of these options are used, maps takes precedence over urls which takes precedence over values loaded from an eik.json file.

ie. in the following example

export default {
    input: 'source/main.js',
    plugins: [eikImportMapPlugin({
        path: '/path/to/eik-json-folder',
        urls: ['http://myserver/import-map'],
        maps: [{
          imports: {
            "lit-element": "https://cdn.eik.dev/lit-element/v2",
          }
        }],
    })],
    output: {
        file: 'build.js',
        format: 'esm'
    }
};

Any import map URLs in eik.json will be loaded first, then merged with (and overridden if necessary by) the result of fetching from http://myserver/import-map before finally being merged with (and overriden if necessary by) specific mappings defined in maps. (In this case lit-element)

Plugin result

Bundles will have bare imports mapped to absolute URLs.

Ie. Something like this...

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

Will be mapped to something like this...

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

Options

This plugin takes an import map as options:

option	default	type	required	details
path	cwd/eik.json	string	false	Path to eik.json file.
urls	[]	array	false	Array of import map URLs to fetch from.
maps	[]	array	false	Array of import map as objects.

Note on the rollup external option

Any mappings defined by any of the means described above must not occur 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: [
    eikImportMapPlugin({
      maps: [{
        imports: {
          "lit-element": "https://cdn.eik.dev/lit-element/v2",
        }
      }],
    }),
  ],
  output: {
    file: "build.js",
    format: "esm",
  },
};

License

Copyright (c) 2020 Finn.no

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.