AngularJS : How to watch service variables?

AngularJS: How to Watch Service Variables?

Sometimes, in AngularJS, we come across situations where we need to watch changes in service variables and update our view accordingly. This can be a bit tricky, especially when we are dealing with shared variables.

Let's take a look at an example scenario. Suppose we have a service called aService with a variable called foo. We want to render a list in our HTML based on the changes in the foo variable.

factory('aService', ['$rootScope', '$resource', function ($rootScope, $resource) {
  var service = {
    foo: []
  };

  return service;
}]);

In our HTML, we have a controller called FooCtrl which uses the aService.foo variable to control the rendering of a list.

<div ng-controller="FooCtrl">
  <div ng-repeat="item in foo">{{ item }}</div>
</div>

To detect changes in aService.foo, we can use the $watch function provided by AngularJS. However, to watch a service variable, we need to add the service to the controller's $scope and then use $scope.$watch(). Here's how it can be done:

function FooCtrl($scope, aService) {
  $scope.aService = aService;
  $scope.foo = aService.foo;

  $scope.$watch('aService.foo', function (newVal, oldVal, scope) {
    if(newVal) {
      scope.foo = newVal;
    }
  });
}

This solution works, but it feels a bit lengthy and repetitive, especially if we have multiple controllers using the same service variables.

Is there a better way to accomplish watching shared variables?

Fortunately, AngularJS provides a more elegant solution for watching shared service variables. We can use the $rootScope to reduce the boilerplate code. Here's how:

function FooCtrl($scope, aService, $rootScope) {
  $scope.foo = aService.foo;

  $rootScope.$watch(function() {
    return aService.foo;
  }, function(newVal, oldVal) {
    if(newVal) {
      $scope.foo = newVal;
    }
  });
}

By utilizing the $rootScope instead of adding the service to the controller's $scope, we eliminate the need for extra code. The $rootScope.$watch function allows us to directly watch the aService.foo variable and update the foo variable in our view whenever a change occurs.

🎉🎉 That's it! You have now learned how to efficiently watch service variables in AngularJS. No more repetitive code or hassle.

If you found this blog post helpful, make sure to share it with your fellow AngularJS enthusiasts. Comment down below if you have any questions or if you want to share any other AngularJS tips and tricks.

Keep coding like a 🌟 AngularJS guru! Happy coding!