Dave Long Dave Long - 6 months ago 9
Javascript Question

Using $scope.$watch when using `this` scope in controller

I have a controller in my Angular app:

(function (angular) {
function MyController() {
this.name = 'Dave';

// I want to have code like this:
/*
$scope.$watch('name', function (newValue, oldValue) {
console.log(oldValue, "changed to", newValue);
});
*/
}

window.myApp = angular.module('myApp', [])
.controller('MyController', [MyController]);
})(angular);


Is there a way to use the features of
$scope.$watch
when attaching values to the
MyController
prototype?

I did notice that in my code, if I add something like
ng-controller="MyController as myCtrl"
, and change my
$scope.$watch
statement to
$scope.$watch('myCtrl.name', ...)
, it'll work after I add the
$scope
dependency, but that feels like tying my controller to my views, which feels wrong.

Edit

To attempt to clarify on what I'm asking. My HTML is something like this:

<div ng-app="myApp">
<div ng-controller="MyController as myCtrl">
<input type="text" ng-model="myCtrl.name" />
<p>{{myCtrl.helloMessage}}</p>
</div>
</div>


My controller is something like this:

angular.module('myApp', [])
.controller('MyController', ['$scope', function ($scope) {
this.name = 'World';
this.helloMessage = "Hello, " + this.name;

var self = this;
$scope.$watch('myCtrl.name', function () {
self.helloMessage = "Hello, " + self.name;
});
}]);


That currently works, but as you can see, in the
$watch
call, I have to reference my controller by the
controllerAs
name from my view, which is less than ideal.

I've setup an example on Plunkr

Answer

$watch

Expression that is evaluated on each $digest cycle. A change in the return value triggers a call to the listener. Watch expression can be a sting or function.

  • string: Evaluated as expression
  • function(scope): called with current scope as a parameter.

example

angular.module('app', []).controller('MainCtrl', function($scope) {
  this.name = 'World'
  this.helloMsg = ''
  
  $scope.$watch(function() {
    return this.name
  }.bind(this), function(newName) {
    this.helloMsg = "Hello, " + newName
  }.bind(this))
});
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>

<div ng-app='app'>
  <div ng-controller='MainCtrl as ctrl'>
    <input type='text' ng-model='ctrl.name' />
    {{ ctrl.helloMsg }}
  </div>
</div>