AngularJS directive scope not updating when value changed outside of AngularJS

Question

I am getting started with AngularJS and have a noob problem that I am not sure how to resolve. I am modifying a value outside of angular (I have put it in the .run section only for demonstration purposes), and then attempting to run $apply so that Angular will notice that the scope needs to be updated.

However, in the following code, the {{currentState}} value gets set to "Initial value" and does not ever update to "Second value".

What is the correct approach to get the value to update?

angular.module("exampleApp", [])
.run(function(userNotificationService) {
    userNotificationService.setStatus("Initial value");
    setTimeout(function() {
       userNotificationService.setStatus("Second value");
    }, 1000);
})
.factory('userNotificationService', function($rootScope) {
   var currentState = 'Unknown state'; // this should never be displayed
   return {
     setStatus: function(state) {
        $rootScope.$apply(function() {
            currentState = state;
        });
     },
     getStatus: function() {
        return currentState;
     }
  };
}).directive('currentState', function(userNotificationService) {
    return {
        restrict: 'AE',
        scope: false, // set to false so that directive scope is used for transcluded expressions
        link: function(scope) {
            scope.currentState = userNotificationService.getStatus();
        }
    };
}).controller("defaultCtrl", function ($scope) {
// does nothing
});

And the html is the following:

<body ng-controller="defaultCtrl">
    <div current-state>
        current state: {{ currentState }}
    </div>
</body>

musically_ut · Accepted Answer · 2014-07-10 21:30:42Z

2

If your use-case involves a timer, then Angular provides its own timer service called $interval which wraps the call in a scope.$apply for you. You should use that instead of setTimeout.

Now in this case, since you need a one way binding between a service and a value in your scope, you can set up a $watch in your directive:

 .directive('currentState', function(userNotificationService) {
    return {
        restrict: 'AE',
        scope: false, // set to false so that directive scope is used for transcluded expressions
        link: function(scope) {
            scope.$watch(function () { return userNotificationService.getStatus(); }, function (newVal) {
                scope.currentState = userNotificationService.getStatus();
             });
        }
    };

Ideally how you would do it is by creating this one way (or two way) binding in your controller (which you have left empty). The $scope you define on the controller will be available to the directive (if you set $scope: false or $scope: true), and then you can leave the link function empty.

edited Jul 10, 2014 at 21:30

answered Jul 10, 2014 at 21:24

musically_ut

34.3k9 gold badges98 silver badges110 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Alexander Marquardt Over a year ago

scope.currentState = newVal works too, as opposed to calling userNotificationService.getStatus() again.

musically_ut Over a year ago

@AlexanderMarquardt It depends. On the first execution, the newVal may be undefined if the first argument to $watch is a string. If the operation is expensive, then it may be better to use newVal and guard against undefined-edness.

Collectives™ on Stack Overflow

AngularJS directive scope not updating when value changed outside of AngularJS

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related