@ramitos/critters

Critters

Critters is a Webpack plugin that inlines your app's critical CSS and lazy-loads the rest.

critters-webpack-plugin

It's a little different from other options, because it doesn't use a headless browser to render content. This tradeoff allows Critters to be very fast and lightweight. It also means Critters inlines all CSS rules used by your document, rather than only those needed for above-the-fold content. For alternatives, see Similar Libraries.

Critters' design makes it a good fit when inlining critical CSS for prerendered/SSR'd Single Page Applications. It was developed to be an excellent compliment to prerender-loader, combining to dramatically improve first paint time for most Single Page Applications.

Features

• Fast - no browser, few dependencies
• Integrates with html-webpack-plugin
• Works with webpack-dev-server / webpack serve
• Supports preloading and/or inlining critical fonts
• Prunes unused CSS keyframes and media queries

Installation

First, install Critters as a development dependency:

npm i -D critters-webpack-plugin

Then, import Critters into your Webpack configuration and add it to your list of plugins:

// webpack.config.js
+const Critters = require('critters-webpack-plugin');

module.exports = {
  plugins: [
+    new Critters({
+      // optional configuration (see below)
+    })
  ]
}

That's it! Now when you run Webpack, the CSS used by your HTML will be inlined and the imports for your full CSS will be converted to load asynchronously.

Usage

Critters

Create a Critters plugin instance with the given options.

Parameters

• options Options Options to control how Critters inlines CSS.

Examples

// webpack.config.js
module.exports = {
  plugins: [
    new Critters({
      // Outputs: <link rel="preload" onload="this.rel='stylesheet'">
      preload: 'swap',

      // Don't inline critical font-face rules, but preload the font URLs:
      preloadFonts: true
    })
  ]
}

Options

All optional. Pass them to new Critters({ ... }).

Type: Object

Properties

• external Boolean Inline styles from external stylesheets (default: true)
• preload String Which preload strategy to use
• noscriptFallback Boolean Add <noscript> fallback to JS-based strategies
• inlineFonts Boolean Inline critical font-face rules (default: false)
• preloadFonts Boolean Preloads critical fonts (default: true)
• fonts Boolean Shorthand for setting inlineFonts+preloadFonts- values:
  • true to inline critical font-face rules and preload the fonts
  • false to don't inline any font-face rules and don't preload fonts
• compress Boolean Compress resulting critical CSS (default: true)

PreloadStrategy

The mechanism to use for lazy-loading stylesheets. [JS] indicates that a strategy requires JavaScript (falls back to <noscript>).

• default: Move stylesheet links to the end of the document and insert preload meta tags in their place.
• "body": Move all external stylesheet links to the end of the document.
• "media": Load stylesheets asynchronously by adding media="not x" and removing once loaded. [JS]
• "swap": Convert stylesheet links to preloads that swap to rel="stylesheet" once loaded. [JS]
• "js": Inject an asynchronous CSS loader similar to LoadCSS and use it to load stylesheets. [JS]
• "js-lazy": Like "js", but the stylesheet is disabled until fully loaded.

Type: (default | "body" | "media" | "swap" | "js" | "js-lazy")

Similar Libraries

There are a number of other libraries that can inline Critical CSS, each with a slightly different approach. Here are a few great options:

• Critical
• Penthouse
• webpack-critical
• webpack-plugin-critical
• html-critical-webpack-plugin
• react-snap

License

Apache 2.0

This is not an official Google product.