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🦸‍♂️ webp-hero

browser polyfill for the webp image format

  • 📦 npm install webp-hero
  • 🎉 webp images come alive, even in safari and ie11! (firefox and edge now support webp)
  • ⚙️ webp-hero actually runs google's libwebp decoder in the browser (converts webp images to png on-the-fly)
  • 🕹️ live demo
    • webp-hero/ — webp-hero polyfill operating normally (does nothing if your browser supports webp)
    • webp-hero/?force — webp conversion to png is forced (even if your browser supports webp)
    • webp-hero/?force&useCanvasElements — wholly replace webp image elements with canvas elements (added for icecat compatibility)
  • ♻️ freshness
  • 💯 browser support tested 2020-08-26
    • evergreen browsers (chrome, firefox, edge, desktop safari)
    • windows 7 ie11
    • iphone 7 mobile safari
    • galaxy s5 samsung internet
    • icecat 60.7 (requires option {useCanvasElements: true})
  • ⚖️ 98 KB
  • ⚠️ known issues and deficiencies
    • doesn't yet support css background images (pull requests welcome!)
    • doesn't yet support <picture> elements
    • doesn't yet support web workers (decodes images one-at-a-time, blocking, single-threaded)
    • no wasm (because older browsers)

webp-hero installation and usage

  • option A — html install, use webp-hero's bundle with the polyfills
    you just inject the html onto your page. this technique works nicely for older browsers like ie11

    1. load generic polyfills and the webp-hero global bundle via script tags

      <script src=""></script>
      <script src=""></script>
    2. run the webp-hero polyfill function on the document

      	var webpMachine = new webpHero.WebpMachine()
  • option B — commonjs install, use webp-hero's cjs modules in your application
    you'll be familiar with this if you're bundling a commonjs with browserify or webpack

    1. install the webp-hero npm package

      npm install webp-hero

    2. import and run the webp-hero polyfill function

      import {WebpMachine} from "webp-hero"
      const webpMachine = new WebpMachine()
    3. if you want to support old browsers like ie11,
      you might want to include your own polyfills or import webp-hero/dist-cjs/polyfills.js

  • option C — es-module install, like in the future
    es modules are available. but why would anybody use these for webp-hero? i guess it could be useful for.. mobile safari? anyways, this won't work in older browsers, which might defeat the purpose of using webp-hero in the first place? well.. it's here for you if you need it!

    1. use webp-hero on your page in one script tag

      <script type="module">
      	import {WebpMachine} from ""
      	const webpMachine = new WebpMachine()
  • option D — angular users should look at ngx-webp-polyfill

webp-hero advanced usage


  • webp-machine.ts has logic for polyfilling, caching, and enforcing sequential webp decoding
    • new WebpMachine({...options}) — all options have defaults, but you can override them
      • {webp} google module which contains the actual decoder
      • {webpSupport} function which detects whether the browser supports webp
      • {detectWebpImage} detect whether or not the provided <img> element is in webp format
      • {useCanvasElements: true} boolean which when true causes webp-hero to polyfill webp images by wholly replacing them with canvas elements (instead of using png data urls). this helps compatibility with icecat (default: false)
    • the webpMachine you create has the following methods
      • webpMachine.polyfillDocument() — run over the entire html document, sniffing out webp <img> elements to convert (only if the browser doesn't support webp)
      • webpMachine.polyfillImage(imageElement) — converts the given webp image (only if the browser doesn't support webp)
      • webpMachine.decode(webpData) — decode webp Uint8Array data, return a png data-url
      • webpMachine.clearCache() — manually wipe the cache to save memory
  • other modules like convert-binary-data.ts and etc may be unstable, you might not want to rely on those

manual-style with the google libwebp decoder

  • we compile from google's libwebp emscripten build in a docker container
  • this build contains minimal functionality for rendering webp data to a canvas:
    • google's emscripten output: webp-hero/libwebp/google/webp.js
  • we do little hacks to wrap this build into two modules:
    • common-js: webp-hero/libwebp/webp.cjs.js
    • es-module: webp-hero/libwebp/webp.js
  • we have a typescript declaration for it too: webp.d.ts

webp-hero dev and contributing

  • prerequisites

    • git and node
    • docker (only if you want to rebuild google's libwebp)
  • webp-hero development

    • npm install — install dependencies and run build
      • runs a typescript build, uses browserify to make the bundle
      • generates webp-hero/dist/ and webp-hero/dist-cjs/
      • generates the polyfills (cjs-only)
      • does not rebuild google's libwebp
    • npm start — start http server
  • rebuild google's libwebp

    • libwebp build artifacts in libwebp/dist are checked into git, because it takes so damn long to build
    • libwebp/build — run dockerized libwebp build, regenerates libwebp/dist
    • libwebp/debug — handy for debugging the dockerized build