rollup-plugin-hot-css

A generic CSS loader for Rollup. Supports Hot Module Replacement when used with Nollup. If the CSS imports any assets such as images or fonts, those URLs are resolved with assets emitted.

How to use

npm install rollup-plugin-hot-css

let hotcss = require('rollup-plugin-hot-css');

module.exports = {
    ...
    plugins: [
        hotcss({
            file: 'styles.css',
            extensions: ['.css', '.scss'],
            loaders: ['scss'],
            hot: true
        })
    ]
}

Options

• String file - Output file name. Default is styles.css. The final name of this file will be based on assetsFileName Rollup output option.

• Array extensions - Extensions to run the plugin for. Default is .css, .scss, .less

• Function loaders - Array of preprocessors to run. Can accept either a string or a function. The only supported strings are scss and less (note: they must be installed). Passing a custom loader can be done using a function. The function will receive input and id. input will contain code and map with the code and sourcemap so far.

• Boolean hot - Enable hot module replacement using <link> tag. This should be disabled if building for production. Default is false.

• Boolean url - Enable resolving URLs found in CSS file and export those assets. This will resolve after all other loaders. Sourcemaps must be emitted by the previous loader for this to work. Default is true.

• String publicPath - Used by HMR. If the app is not being hosted on the root of the domain but instead in a subdirectory, use this option to provide the path prefix. Default is /.

Loaders

There are two built in loaders: scss and less. Custom loaders can be specified, as described below:

function MyCustomLoader (input, id) {
    // input.code
    // input.map
    // input.watchFiles

    return {
        code: /* transformed code as a string */,
        map: /* source map */,
        watchFiles: /* optional extra files to watch for changes */
    }
}

hotcss({
    loaders: ['scss', MyCustomLoader]
})

Loaders can also be asynchronous by returning a Promise:

function MyCustomLoader (input, id) {
    return new Promise(resolve => ({
        code: /* transformed code as a string */,
        map: /* source map */,
        watchFiles: /* optional extra files to watch for changes */
    }));
}

An example using postcss:

let autoprefixer = require('autoprefixer')
let postcss = require('postcss')

function PostCSSLoader (input, id) {
    return postcss([autoprefixer]).process(input.code).then(res => {
        return {
            code: res.css
        };
    });
}

hotcss({
    loaders: ['scss', PostCSSLoader]
})

Hot Module Replacement

The HMR API expects there to be a link tag inside the index.html file.

<link rel="stylesheet" type="text/css" href="/styles.css">

When file changes are made, the link tag is replaced by appending a timestamp to the end of the href. This forces the browser to download the file again.

Note that the href is based on the assetsFileName option. If using Nollup for example, if your assetsFileName option is set to [name].[hash][extname] then href should be set to /styles.[hash].css.