const path = require('path');
const parse5 = require('parse5');
const nwmatcher = require('nwmatcher');
const css = require('css');
const prettyBytes = require('pretty-bytes');
const treeAdapter = parse5.treeAdapters.htmlparser2;
const PLUGIN_NAME = 'critters-webpack-plugin';
const PARSE5_OPTS = {
treeAdapter
};
/** Critters: Webpack Plugin Edition!
* @class
* @param {Object} options
* @param {Boolean} [options.external=true] Fetch and inline critical styles from external stylesheets
* @param {Boolean} [options.async=false] Convert critical-inlined external stylesheets to load asynchronously (via link rel="preload" - see https://filamentgroup.com/lab/async-css.html)
* @param {Boolean} [options.preload=false] (requires `async` option) Append a new into instead of swapping the preload's rel attribute
* @param {Boolean} [options.fonts] If `true`, keeps critical `@font-face` rules and preloads them. If `false`, removes the rules and does not preload the fonts
* @param {Boolean} [options.preloadFonts=false] Preloads critical fonts (even those removed by `{fonts:false}`)
* @param {Boolean} [options.removeFonts=false] Remove all fonts (even critical ones)
* @param {Boolean} [options.compress=true] Compress resulting critical CSS
*/
module.exports = class CrittersWebpackPlugin {
constructor (options) {
this.options = options || {};
this.urlFilter = this.options.filter;
if (this.urlFilter instanceof RegExp) {
this.urlFilter = this.urlFilter.test.bind(this.urlFilter);
}
}
/** Invoked by Webpack during plugin initialization */
apply (compiler) {
// hook into the compiler to get a Compilation instance...
compiler.hooks.compilation.tap(PLUGIN_NAME, compilation => {
// ... which is how we get an "after" hook into html-webpack-plugin's HTML generation.
compilation.hooks.htmlWebpackPluginAfterHtmlProcessing.tapAsync(PLUGIN_NAME, (htmlPluginData, callback) => {
this.process(compiler, compilation, htmlPluginData)
.then(result => { callback(null, result); })
.catch(callback);
});
});
}
readFile (filename, encoding) {
return new Promise((resolve, reject) => {
this.fs.readFile(filename, encoding, (err, data) => {
if (err) reject(err);
else resolve(data);
});
});
}
async process (compiler, compilation, htmlPluginData) {
const outputPath = compiler.options.output.path;
// Parse the generated HTML in a DOM we can mutate
const document = parse5.parse(htmlPluginData.html, PARSE5_OPTS);
makeDomInteractive(document);
// `external:false` skips processing of external sheets
if (this.options.external !== false) {
const externalSheets = document.querySelectorAll('link[rel="stylesheet"]');
await Promise.all(externalSheets.map(
link => this.embedLinkedStylesheet(link, compilation, outputPath)
));
}
// go through all the style tags in the document and reduce them to only critical CSS
const styles = document.querySelectorAll('style');
await Promise.all(styles.map(
style => this.processStyle(style, document)
));
// serialize the document back to HTML and we're done
const html = parse5.serialize(document, PARSE5_OPTS);
return { html };
}
/** Inline the target stylesheet referred to by a (assuming it passes `options.filter`) */
async embedLinkedStylesheet (link, compilation, outputPath) {
const href = link.getAttribute('href');
const document = link.ownerDocument;
// skip filtered resources, or network resources if no filter is provided
if (this.urlFilter ? this.urlFilter(href) : href.match(/^(https?:)?\/\//)) return Promise.resolve();
// path on disk
const filename = path.resolve(outputPath, href.replace(/^\//, ''));
// try to find a matching asset by filename in webpack's output (not yet written to disk)
const asset = compilation.assets[path.relative(outputPath, filename).replace(/^\.\//, '')];
// CSS loader is only injected for the first sheet, then this becomes an empty string
let cssLoaderPreamble = `function $loadcss(u,l){(l=document.createElement('link')).rel='stylesheet';l.href=u;document.head.appendChild(l)}`;
const media = typeof this.options.media === 'string' ? this.options.media : 'all';
// { preload:'js', media:true }
// { preload:'js', media:'print' }
if (this.options.media) {
cssLoaderPreamble = cssLoaderPreamble.replace('l.href', "l.media='only x';l.onload=function(){l.media='" + media + "'};l.href");
}
// Attempt to read from assets, falling back to a disk read
const sheet = asset ? asset.source() : await this.readFile(filename, 'utf8');
// the reduced critical CSS gets injected into a new