Polyfills

Aurelia comes with a minimal set of polyfills that it requires to work, inside aurelia-polyfills. You don't need to import this package explicitely as aurelia-bootstrapper imports it for you.

Removing polyfills

Maybe you are lucky to target modern browsers only or maybe you import your own set of more complete polyfills.

In those situations, you might want to remove Aurelia's own polyfills from your build. This can reduce the size of your bundle and avoid conflicts between different polyfills.

The plugin features option enables you to remove polyfills from the build output, with varying levels of compliance: ES2015, ES2016, ESnext (for Reflect.metadata and co).

Internet Explorer

To reduce the size of aurelia-polyfills Aurelia does not include commonly implemented features that are missing from Internet Explorer.

If you want to support Internet Explorer, you have to include your own polyfills for the following features:

• Promise is missing from IE9-11.
• MutationObserver is missing from IE9-10.
• requestAnimationFrame is missing from IE9.

Including custom polyfills

If you include your own polyfills instead of -- or in addition to (IE) -- Aurelia's, you need to make sure that they are loaded before any Aurelia module is imported. You should also make sure that they are installed globally as a native implementation would, or maybe try to use Webpack ProvidePlugin.

Good ways to load your polyfills before anything else include:

• Putting them in a separate <script> tag before your bundle script.
• Starting with 2.0 RC3 Putting them in your Webpack entry configuration, before aurelia-bootstrapper.

Example

Let's say we target IE11, so we need to add a Promise polyfill to run properly.

There are many Promise polyfills available, we'll use es6-promise. First step is to add it to our dependencies, e.g. yarn add es6-promise, with npm or manually.

Second step is to add it to webpack.config.js:

module.exports = {
  entry: ["es6-promise/auto", "aurelia-bootstrapper"],
  // ...
};

And voilà it works!

Notice how we imported es6-promise/auto, because according to its documentation this is how we define a global Promise. Importing es6-promise doesn't change the global scope, it only returns a Promise implementation for local usage (see Ponyfills).