AngularJS watch array length change.

angular_app.js

angular.module('myApp', []);

angular.module('myApp').controller('watcherCtrl', ['$scope', function($scope) {
    $scope.myArray = [];
    
    var index = 42;
    $scope.push = function () {
        $scope.myArray.push(index++);
    }
    
    $scope.$watch('myArray.length', function() {
        if ($scope.myArray.length > 0) {
            alert('Index pushed into myArray');
        }
    });
}]);

angular_html.html

<div ng-app='myApp'>
    <div ng-controller='watcherCtrl'>
        <input type='button' title='Push' ng-click='push()'/>
        <ul>
            <li ng-repeat='item in myArray'>{{item}}</li>
        </ul>
    </div>
</div>