ngrepeat tracking

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.2.16/angular.js"></script>
<div ng-app ng-controller='ctrl'>
    <h3>Using $$hashKey</h3>
    <div ng-repeat="task in tasks1">
        <div>{{task}}</div>
        <button ng-click='checkMe(task)'>Check Me</button>
    </div>
    <br/>
    <h3>Using task.id</h3>
    <div ng-repeat="task in tasks2 track by task.id">
        <div>{{task}}</div>
        <button ng-click='checkMe(task)'>Check Me</button>
    </div>

</div>

JavaScript

function ctrl($scope) { 
    $scope.tasks1=[{id:1,text:"one"},{id:1,text:"two"},{id:3,text:"three"}];
    $scope.tasks2=[{id:1,text:"one"},{id:2,text:"two"},{id:3,text:"three"}];
    $scope.checkMe=function(item) {
        console.log(JSON.stringify(item));
    };
}