title: On what factor ng-repeat identify the duplicates in the array of objects?
body: <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
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  <pre class="snippet-code-js lang-js prettyprint-override"><code>angular.module("myApp",[])
         .controller("myCtrl",function($scope) {
           $scope.persons = [{name:"teja",age:11},
                             {name:"Ash",age:12},
                             {name:"teja",age:11}];
                             });</code></pre>
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  <p>Angular doesn't allow duplicate elements in an array declared in <code>ng-repeat</code>.
  But there is solution "<code>track by $index</code>" which can allow duplicate elements in array.
  Here my question is how <code>ng-repeat</code> identify there are duplicate elements in the array that is on what factor it identifies.
  Whenever a new object is created new reference for that object is created  but in the above code how ng-repeat identifies the duplicates.</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
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  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div ng-repeat="person in  persons"&gt;
  {{ person.name }}
  &lt;/div&gt;</code></pre>
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