JSFiddle - React, Tailwind, and code Playground
HTML
<div ng-app="myApp" ng-controller="MyCtrl">
It works without "track by"
<ul>
<li ng-repeat="item in items|orderBy:'toString()'">{{item}}</li>
</ul>
It doesn't work witho "track by"
<ul>
<li ng-repeat="item in items track by $index|orderBy:'toString()'">{{item}}</li>
</ul>
</div>
JavaScript
var myApp = angular.module('myApp',[]);
function MyCtrl($scope) {
$scope.items = ['item 2', 'item 1'];
}