@eik/postcss-plugin

PostCSS Eik plugin to support the use of import maps to map "bare" import specifiers in CSS @import rules.

Installation

$ npm install @eik/postcss-plugin

Usage

const postcss = require('postcss');
const plugin = require('@eik/postcss-plugin');
const fs = require('fs');

// CSS to be processed
const css = fs.readFileSync('css/input.css', 'utf8');

postcss()
    .use(
        plugin()
    )
    .process(css, {
        // `from` option is needed here
        from: 'css/input.css',
    })
    .then(function (result) {
        console.log(result.css);
    });

Description

This plugin transforms "bare" import specifiers to absolute URL specifiers in CSS modules by applying an Import Map ahead of time.

For a more detailed description of Import Maps, please see our Import Maps section.

The main target for Import Maps is to map import statements in EcmaScript Modules but it can be applied to CSS import statements too.

Given the following CSS:

@import 'normalize.css';

body {
    background: black;
}

when applaying the following Import Map:

{
    "imports": {
        "normalize.css": "https://cdn.eik.dev/normalize.css@8/normalize.css",
    },
}

one will get a transformed CSS like so:

@import 'https://cdn.eik.dev/normalize.css@8/normalize.css';

body {
    background: black;
}

Options

This plugin takes the following as options:

option	default	type	required	details
path	process.cwd()	string	false	Path to directory containing a eik.json file or package.json with eik config.
urls	[]	array	false	Array of import map URLs to fetch from.
maps	[]	array	false	Array of import map as objects.

The plugin will attempt to read import map URLs from eik.json or package.json files in the root of the current working directory if present.

postcss()
    .use(
        plugin()
    )
    .process(css, {...})
    .then(...);

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

postcss()
    .use(
        plugin({ path: '/path/to/eik-json-folder' })
    )
    .process(css, {...})
    .then(...);

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

postcss()
    .use(
        plugin({ urls: 'http://myserver/import-map' })
    )
    .process(css, {...})
    .then(...);

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

postcss()
    .use(
        plugin({
            maps: [{
                "imports": {
                    "normalize.css": "https://cdn.eik.dev/normalize.css@8/normalize.css",
                },
            }],
        })
    )
    .process(css, {...})
    .then(...);

Precedence

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

ie. in the following example

postcss()
    .use(
        plugin({
            path: '/path/to/eik-json-folder',
            urls: ['http://myserver/import-map'],
            maps: [{
                "imports": {
                    "normalize.css": "https://cdn.eik.dev/normalize.css@8/normalize.css",
                },
            }],
        })
    )
    .process(css, {...})
    .then(...);

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.

PostCSS Import Usage

If you're using postcss-import make sure you update the plugins option. postcss.config.js

module.exports = (ctx) => ({
    plugins: [
        require('@eik/postcss-plugin')(),
        require('postcss-import')({
            // It needs to be added here as well to ensure everything is mapped
            plugins: [require('@eik/postcss-plugin')],
        }),
    ],
});

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.