Example $parse in expression

HTML

<script src="https://code.angularjs.org/1.3.0/angular.js"></script>
<div ng-app="app" ng-controller="MainCtrl">
    <input ng-model="expr" type="text" placeholder="Enter an expression" />
     <h2>{{ parsedValue }}</h2>
</div>

JavaScript

angular.module("app", [])
.controller("MainCtrl", function ($scope, $parse) {
    $scope.$watch("expr", function (newVal, oldVal, $scope) {
        if (newVal !== oldVal) {
        debugger;
            $scope.parsedValue = $parse(newVal)($scope);
        }
    });
});