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>