AngularJS track by $index

HTML

This will work
<div ng-repeat="value in [4, 4] track by $index">{{value}}</div>

This won't
<!-- <div ng-repeat="value in [4, 4]">{{value}}</div> -->

<div ng-repeat="value in [{id:1}, {id:2}] track by value.id">{{value.id}}</div>