@eik/webpack-plugin

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

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

Installation

$ npm install @eik/webpack-plugin

Usage

export default {
    experiments: {
        outputModule: true,
    },
    entry: '/src/input.js',
    mode: 'production',
    output: {
        environment: {
            module: true,
        },
        filename: 'bundle.js',
        path: '/out/',
    },
    module: {
        rules: [
            {
                test: /\.js$/,
                use: {
                    loader: '@eik/webpack-plugin',
                    options: {
                        path: '/path/to/eik-json-folder' 
                    },
                },
            },
        ],
    },
};

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.

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

export default {
    //...
    module: {
        rules: [
            {
                test: /\.js$/,
                use: {
                    loader: '@eik/webpack-plugin',
                    options: {
                        path: '/path/to/eik-json-folder' 
                    },
                },
            },
        ],
    },
};

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

export default {
    //...
    module: {
        rules: [
            {
                test: /\.js$/,
                use: {
                    loader: '@eik/webpack-plugin',
                    options: {
                        urls: ['http://myserver/import-map']
                    },
                },
            },
        ],
    },
};

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

export default {
    //...
    module: {
        rules: [
            {
                test: /\.js$/,
                use: {
                    loader: '@eik/webpack-plugin',
                    options: {
                        maps: [{
                            imports: {
                                "lit-element": "https://cdn.eik.dev/lit-element/v2",
                            }
                        }],
                    },
                },
            },
        ],
    },
};

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 {
    //...
    module: {
        rules: [
            {
                test: /\.js$/,
                use: {
                    loader: '@eik/webpack-plugin',
                    options: {
                        path: '/path/to/eik-json-folder',
                        urls: ['http://myserver/import-map'],
                        maps: [{
                            imports: {
                                "lit-element": "https://cdn.eik.dev/lit-element/v2",
                            }
                        }],
                    },
                },
            },
        ],
    },
};

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 the following 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 ESM with WebPack

This plugin will only apply import maps to ESM modules. Due to this its more or less given that the source of your build must be ESM and that your build output is ESM. WebPack does not by default output ESM so this needs to be configured.

You enable ESM output in WebPack as follows (reference):

export default {
  //...
  experiments: {
    outputModule: true,
  },
  output: {
    environment: {
        module: true,
    },
  },
};

License

See license file.