Use of $parse in angular js

Angular runs $parse automatically when it runs the $digest loop, basically $parse is the way angular evaluates expressions. If you wanted to manually parse an expression, you can inject the $parse service into a controller and call the service to do the parsing for you.

Here’s a code snipped from ng-book that watches then parses an expression.

<div ng-controller="MyCtrl">
  <input ng-model="expr" type="text" placeholder="Enter an expression" />
    <h2>{{ parsedValue }}</h2>
</div>

then in our module,

angular.module("myApp", [])
 .controller('MyCtrl',['$scope', '$parse', function($scope, $parse) {
    $scope.$watch('expr', function(newVal, oldVal, scope) {
      if (newVal !== oldVal) {
        // Let's set up our parseFun with the expression
        var parseFun = $parse(newVal);
        // Get the value of the parsed expression
         $scope.parsedValue = parseFun(scope);
      }
    });
 }]);