Web Components Polyfills
Getting Started | Usage | Packages | Roadmap
If you use Custom Elements, Shadow DOM, or the
<template> element, either
directly or through a library like
LitElement, then you can use these
polyfills to make your app work in older browsers like IE11.
We're also working on polyfills for cutting edge new APIs for Web Components that aren't built into all modern browsers yet, like Shadow Parts and Adopted Stylesheets.
webcomponentsjs package to get all of the Web Components
polyfills and a loader that automatically downloads only the polyfills each
npm install --save @webcomponents/webcomponentsjs
Load the polyfills loader before any of your application code:
<html> <head> <!-- If your application is compiled to ES5, then load this script first. --> <script src="./node_modules/@webcomponents/webcomponentsjs/custom-elements-es5-adapter.js"></script> <!-- Add support for Web Components to older browsers. --> <script src="./node_modules/@webcomponents/webcomponentsjs/webcomponents-loader.js"></script> <!-- Load your application code anytime after loader.js --> </head> <body> <!-- Your custom elements will work in older browsers like IE11. --> <my-custom-element></my-custom-element> </body> </html>
For more ways to load the Web Components polyfills, see the webcomponentsjs package.
The Web Components polyfills handle many usage patterns automatically, but there are certain patterns that require direct interaction with the library:
Setting Custom Properties
To set a CSS custom property value imperatively, pass the value to
To re-compute CSS custom properties after a DOM mutuation that affects the matching condition of a CSS rule containing a custom property (e.g. changing a
To use a style in the main document that sets or consumes a CSS Custom Property, register it with
To use a style in a Custom Element, pass the element's template to
prepareTemplatebefore first cloning it. (Note that LitElement and the Polymer Library perform this registration step automatically.)
This repo is a monorepo. Each package lives under
Loader and pre-minimized bundles for the full suite of Web Components polyfills.
Most users only need to install this package, but it is also possible to separately install any of the individual polyfills listed below.
Polyfill for Scoped CSS (Spec)
Polyfill for HTML Imports (Spec)
Note that HTML Imports are
As of Chrome 81, HTML Imports are no longer natively supported by any browser.
The current version of the Web Components loader does not automatically
polyfill HTML Imports. Applications that still depend on HTML Imports are
recommended to install
@webcomponents/html-imports and load it separately.
The following APIs are on the roadmap for 2020: