readme.md

Awesome Webpack Perf

A curated list of webpack tools and plugins that help make the web faster

Contents

• Built-in stuff
• JS minifiers
• CSS
  • Minifiers
  • Other optimizers
  • Extraction plugins
  • Critical CSS plugins
• CSS-in-JS
  • Minification
  • Zero-runtime libraries
• Images
  • Image compression tools: universal
  • Image compression tools: for a single format
  • Other tools
• Fonts
• Gzip/Brotli
• Service workers
• <link rel> and <script async>
• Prerendering
• Progressive web apps (PWA)
• Analysis tools
  • Bundle contents
  • Code duplicates
  • Various tools
• Webpack build performance
• Other web performance lists

Built-in stuff

• mode: 'production' in the webpack config enables the common production optimizations
• optimization.splitChunks in the webpack config enables splitting one bundle into smaller chunks. This helps to load less JS for each page and cache better
• optimization.runtimeChunk in the webpack config enables splitting webpack’s runtime code into a separate chunk. This improves long-term caching

JS minifiers

JS minifiers are tools that make JS payloads smaller.

• uglifyjs-webpack-plugin – Uglify is an ES5 minifier
• terser-webpack-plugin – Terser is a fork of Uglify that has support for ES2015+. Ships with webpack
• babel-minify-webpack-plugin – Babel Minify is a minifier built in the Babel pipeline. It supports all syntax Babel supports
• closure-webpack-plugin – Closure Compiler is a minifier developed by Google. It has several advanced optimizations that are unsafe for some apps but compress better
• esbuild-webpack-plugin – ESBuild is a JS&TS compiler/minifier written in Go. It’s ~50-100× faster compared to native JavaScript tools.

CSS

Minifiers

CSS minifiers are tools that make the volume of CSS smaller.

There’re three popular competing CSS minifiers: CSSO, CSS Nano and Clean CSS. They’re mostly similar in the compression quality and supported features, so if you’re picking one, just choose the one you prefer more.

• CSSO :

  • csso-loader
  • postcss-csso is a PostCSS plugin that can be used with postcss-loader
  • csso-webpack-plugin only works when you use a CSS extraction plugin. However, it compresses CSS better than the loader – e.g., it can merge rules from multiple source files

• CSS Nano :

  • cssnano is a PostCSS plugin that can be used with postcss-loader
  • optimize-css-assets-webpack-plugin, technically, works with any minifier, but ships (and works best) with cssnano.
    This plugin only works when you use a CSS extraction plugin. However, it compresses CSS better than the loader – e.g., it can merge rules from multiple source files

• Clean CSS :

  • clean-css-loader
  • postcss-clean is a PostCSS plugin that can be used with postcss-loader

Other optimizers

• purgecss-webpack-plugin analyzes the app code and styles and removes CSS rules that aren’t used anywhere. Works great with CSS frameworks like Bootstrap

Extraction plugins

By default (with a simple style-loader), all styles imported in the app are added into the JS bundle. CSS extraction plugins help to move these styles into a separate .css file – which helps with faster rendering and better caching.

• mini-css-extract-plugin is the de-facto default solution for extracting styles in modern webpack
• extract-text-webpack-plugin was the most popular plugin for extracting styles in webpack 1-3
• extract-css-chunks-webpack-plugin has the same API as mini-css-extract-plugin but offers better hot module replacement support

Critical CSS plugins

Critical CSS is an approach for rendering the site faster. With Critical CSS, for each page, you extract the rules needed for the initial render and inline them. Then, you load the remaining styles asynchronously. More details

• html-critical-webpack-plugin runs the critical tool on every webpack build. Uses a headless browser, returns styles only for the above-the-fold content
• critters-webpack-plugin renders HTML in a JSDom environment on every webpack build. Doesn’t use a headless browser (= less heavy); returns all styles needed by the page, not only the above-the-fold ones (= may fix some html-critical-webpack-plugin glitches)
• isomorphic-style-loader helps to extract critical styles during server-side rendering

CSS-in-JS

Minification

CSS-in-JS libraries typically provide Critical CSS support out of the box and need fewer manual optimizations. However, they still need minification.

• minify-cssinjs-loader works with all CSS-in-JS libraries thanks to regex-based matching. Does basic compression of style strings
• Library-specific Babel plugins. Many popular CSS-in-JS libraries have Babel plugins specifically created for them. They typically do a better job at optimization:
  • babel-plugin-styled-components
  • babel-plugin-emotion

Zero-runtime libraries

Most CSS-in-JS libraries ship with a runtime – a chunk of JavaScript that runs in the browser and makes the library work. That makes them easy to use but brings noticeable performance costs.

However, there’re also several CSS-in-JS libraries that don’t use a runtime and don’t suffer from worse performance. They rely on build-time transformations instead:

• linaria: works with linaria/loader and mini-css-extract-plugin (instructions)
• astroturf: works with astroturf/loader and mini-css-extract-plugin (instructions)

Images

Image compression tools: universal

All the tools below optimize .png, .jpg, .gif and .svg images. They’re based on imagemin and imagemin plugins, so they typically result in a similar level of compression.

Pick plugins over loaders. Plugins will optimize images that were produced by other loaders or plugins, whereas loaders will only trigger for files from your source code.

• image-webpack-loader
• img-loader
• imagemin-webpack
• imagemin-webpack-plugin

Image compression tools: for a single format

The below tools focus on a specific format of images.

• svgo-loader optimizes .svg images by passing them through svgo
• svg-sprite-loader combines multiple .svg images into a single sprite
• webp-loader converts images to the webp format

Other tools

• lqip-loader generates low-quality image placeholders which you can use for lazy-loading images. Just like in Medium:

  

• responsive-loader resizes one image to multiple various sizes. Works great with <img srcset> or <picture>

• svg-url-loader generates 20-30% smaller data-urls for inline SVG images

Fonts

• google-fonts-webpack-plugin downloads Google Fonts to the build directory for self-hosting
• fontmin-webpack minifies icon fonts to just what’s used

Gzip/Brotli

Gzip/Brotli compressors compress text so it’s smaller when served over the network.

Normally, this is done by a server like Apache or Nginx on runtime; but you might want to pre-build compressed assets to save the runtime cost.

• compression-webpack-plugin works for Gzip and Brotli
• brotli-webpack-plugin works for Brotli

Service workers

• service-worker-loader takes a file, emits it separately from the bundle, and exports a function to register the file as a service worker:

  import registerServiceWorker from 'service-worker-loader!./sw.js';
  
  registerServiceWorker({ scope: '/' });

• workbox-webpack-plugin prefetches all webpack assets in the background and makes the app ready for working offline. It is based on Google’s workbox library that simplifies common usages of service workers

• offline-plugin also prefetches all webpack assets in the background and makes the app ready for working offline. It falls back to AppCache in browsers that don’t support service workers

<link rel> and <script async>

• preload-webpack-plugin preloads asynchronous chunks¹ with <link rel="preload"> or <link rel="prefetch">
• html-webpack-preconnect-plugin adds <link rel="preconnect"> for a separate domain (e.g., an API server)
• script-ext-html-webpack-plugin adds async or defer attributes to bundle scripts

¹ Asynchronous chunks are chunks that are created when you use import().

Prerendering

Prerendering tools run an app during the build and return the HTML the app generates. This is an alternative to server-side rendering and helps to deliver the content to the user immediately – instead of making them wait until the bundle is loaded.

• prerender-spa-plugin
• prerender-loader

Progressive web apps (PWA)

• webpack-pwa-manifest generates a manifest.json and resizes app icons for a PWA

Analysis tools

Bundle contents

The following tools show relative sizes of all bundled modules. Use them to figure out what takes so much size and can be removed:

• webpack-bundle-analyzer is a webpack plugin. During the build, it generates an interactive HTML page with all bundle modules:

  

  ^{(Animation credits: webpack-bundle-analyzer)}

• Webpack Visualizer is a website that operates on webpack stats (webpack --json > stats.json). It lets you upload the stats.json file and see the bundle contents:

  

• source-map-explorer is a CLI tool that generates bundle stats based on source maps. It’s less detailed than webpack-bundle-analyzer – but you don’t need to reconfigure webpack to run it:

  

  ^{(Image credits: source-map-explorer)}

• bundle-wizard is a CLI tool that also generates bundle stats based on source maps. But, unlike source-map-explorer, it does that for a full page and includes all bundles:

  

Code duplicates

These tools help to find and remove duplicated code inside the bundles:

• Bundle Buddy shows which bundles include which module. Use it to find duplicated code and fine-tune code splitting:

  

• duplicate-package-checker-webpack-plugin prints a warning if a bundle includes multiple versions of the same library:

  

  ^{(Image credits: duplicate-package-checker-webpack-plugin)}

Various tools

• Webpack Analyse shows all modules in the bundle – and why they are bundled. Use it to understand why you are loading that specific huge library:

  

• Statoscope also shows all modules present in the bundle – and why they are bundled. It’s like the Webpack Analyse (the previous tool) but modern and more convenient:

  

  Also, it provides a stats validator that helps you to validate your stats on CI.

• Bundlephobia reports bundle sizes of JS libraries:

  

• webpack-dashboard reports sizes of modules and warnings like duplicated files during development:

  

  ^{(Image credits: webpack-dashboard)}

Webpack build performance

The following tools show how to optimize your webpack build speed.

• speed-measure-webpack-plugin is a webpack plugin. During the build, the plugin measures your webpack build speed, giving an output like this:

  

^{(Animation credits: speed-measure-webpack-plugin)}

Other web performance lists

• Awesome WPO – A curated list of Web Performance Optimization
• Webpack Libs Optimizations – A collection of Babel and webpack plugins to optimize the size of various popular libraries

Contribute

Contributions welcome! Read the contribution guidelines first.

License

To the extent possible under law, Ivan Akulov has waived all copyright and related or neighboring rights to this work.