$watch inside a service?

Question

Is it possible to set up a $watch on an array of objects inside a service (I'd like the $watch declaration itself to be inside the service)?

Answer 1

You can add any expression to the set of watches by injecting the $rootScope and using a function a first argument to the $watch method. Pseudo-code:

$rootScope.$watch(function() {   return //value to be watched; }, function watchCallback(newValue, oldValue) {   //react on value change here }); 

Don't forget about the third, Boolean argument to the $watch method. You need to specify true if you want to deep-watch an entire object for changes.

Answer 2

services by their very nature are like classes and house methods. You can set up a method which you call from your controller who's argument is the scope and applies a watch expression:

app.service('myservice',function(){     this.listen = function($scope) {         $scope.$watch(function(){return someScopeValue},function(){            //$scope.dosomestuff();         });     } });  //your controller  function myCtrl($scope,myservice) {     $scope.listen = function() {         myservice.listen($scope);     }      //call your method     $scope.listen(); } 

update: If you are trying to watch a private local variable inside of a service, see the accepted answer using $rootScope. If you are trying to $watch a $scope variable within a local scope than the above is your best bet. They are achieving two very different things.