AngularJs scope.$watch, $watchgroup and $watchCollection

$watch service helps us to do something or run any business logic when any property or variable value attached to $scope changed

$watch(variable, listener)

function MyController($scope) {

   $scope.myVar = 1;

   $scope.$watch('myVar', function() {

       alert('hey, myVar has changed!');

   });

   $scope.buttonClicked = function() {

      $scope.myVar = 2; // This will trigger $watch expression to kick in

   };

}

There are some other additional angular service $watchCollection and $watchgroup .

Scope.$ watchgroup: it helps us to watch a set of group of variables together , if anyone of them is changed, it will trigger $watchGroup expression.

$watchGroup(watchExpression, listener)

Scope.$watchCollection : it helps us to watch whole object’s properties , we need to pass object instead of each properties of object.

$watchGroup(watchobject, listener)


Other related links : 
AngularJs :$broadcast () , $on() and $emit()

Angularjs : foreach loop

Angularjs : Model or Popup window by ngDialog API