callback function in AngularJS -

i m trying assign value variable in callback function. how know callback functions asynchronous tried scope.apply doesnt seems work.. ideas ?

angular.module("sadf")      .factory("browserscamerasupportservice", function ($scope, $apply ) {          return {              supportsgetusermedia: function () {                  navigator.getusermedia = navigator.getusermedia || navigator.webkitgetusermedia || navigator.mozgetusermedia || navigator.msgetusermedia;                 var hascam = true;                 if (navigator.getusermedia) {                     navigator.getusermedia({video: true}, function(localmediastream){                      }, function(){                          $scope.$apply(function(){                             hascam = false;                         });                     });                 }                 return angular.isdefined(navigator.getusermedia)&& hascam;             }         };     }); 

this case using $apply not need. since check media asynchronous operation convenient return promise object , work in consuming code. service become:

angular.module("sadf")  .factory("browserscamerasupportservice", function($q) {      return {          supportsgetusermedia: function() {              navigator.getusermedia = navigator.getusermedia || navigator.webkitgetusermedia || navigator.mozgetusermedia || navigator.msgetusermedia;              return $q(function(resolve, reject) {                 if (navigator.getusermedia) {                     navigator.getusermedia({video: true}, function(localmediastream) {                         return resolve(true);                     }, function() {                         return resolve(false);                     });                 }             });         }     }; }); 

and usage simple:

browserscamerasupportservice.supportsgetusermedia().then(function(supported) {     if (!supported) {         alert('video not supported.');     } }); 

demo: http://plnkr.co/edit/btj6dehrivka2vk3kn1m?p=preview