webcomponents.js is a set of polyfills built on top of the Web Components specifications. It makes it possible for developers to use these standards today across all modern browsers.

As these technologies are implemented in browsers, the polyfills will shrink and you'll gain the benefits of native implementations. webcomponents.js automatically detects native support and switches to the fast path when available. Your elements seamlessly start relying on the native stuff--and get faster in the process.

Although most developers will want to use everything in webcomponents.js, the polyfills are designed to be used separately, as well. They're available independently as part of the default release download and can also be built standalone. For example, Mozilla's x-tags and Brick projects use a subset of the webcomponents.js polyfills.

Note: The webcomponents.js polyfill layer is no longer needed for browsers that fully implement the Web Components APIs, such as Chrome 36+.

What's in webcomponents.js?

The polyfills are a bundle that includes the following libraries:

Note: A lighter webcomponents-lite.js build is included with the default download package including support for just Custom Elements and HTML Imports. This is useful if you don't require Shadow DOM in your application. You can generate custom builds supporting any combination of Web Component features too.

Installation & usage

To start using these features today, first download webcomponents.js using Bower:

bower install --save webcomponentsjs

Then, include webcomponents.js as you would any other script:

<script src="bower_components/webcomponentsjs/webcomponents.js"></script>

Alternatively, you can install the Web Component polyfills using npm:

npm install --save webcomponents.js

Then, include webcomponents.js as you would any other script:

<script src="node_modules/webcomponents.js/webcomponents.js"></script>

Note: Due to the nature of some of the polyfills, to maximize compatibility with other libraries, make sure that webcomponents.js is the first script tag in your document's <head>.

Once included, you can use HTML Imports, Custom Elements, Shadow DOM, and other emerging standards within your app. For example, to use a webcomponents.js element, just import it using an HTML Import:

<link rel="import"

Then use <paper-tabs> just like any built-in tag.

While each polyfill can be built as a standalone, the recommended approach is to include the entire webcomponents.js file. This ensures all dependencies are present and the largest portion of the future web platform is available. Since this is the most-used configuration, it is also the most tested.

Building each polyfill

For information on how to build each polyfill library independently, see Manually Building.

Next steps

webcomponents.js is a wonderful foundation for working with Web Components in a cross-browser fashion. If you're ready to start building your own elements, and would like to learn about the additional features webcomponents.js, read our guide on Custom Elements.