Firestore Mixin Does Not Work With Internet Explorer 11

[halloweenman]

Description

I've added the Firestore Mixin to latest version of Polymer Starter Kit and it does not work in IE 11. IE 11 just shows a blank screen.

Expected outcome

I would have expected the Polymer Starter Kit to work as normal.

Actual outcome

Blank screen, nothing.

Steps to reproduce

Add/amend the following to starter kit my-app.html:

<link rel="import" href="../bower_components/polymerfire/firebase-app.html">
<link rel="import" href="../bower_components/polymerfire/firebase-firestore-mixin.html">

<firebase-app auth-domain="..." database-url="..." api-key="..." project-id="..."> </firebase-app>

class MyApp extends Polymer.FirestoreMixin(Polymer.Element) {
...
}
window.customElements.define(MyApp.is, MyApp);

When building use build --js-compile so that build is compiled to ES5 for IE 11 compatibility.

Browsers Affected

• [x ] IE 11

[halloweenman]

One problem may be the mixin is using Object.assign which is not supported in IE.

Polymer officially currently supports IE11, as does Firestore.