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JavaScript AngularJS An Introduction to Two-Way Data Binding Two-Way Binding: watchers

Matthew Kosloski
Matthew Kosloski
8,932 Points
Posted by Matthew Kosloski
Matthew Kosloski
8,932 Points

Cannot create $watch with Angular?

What's wrong with this code? It's the same as the code Alex used, but without the factory. Also, how does Angular know what the values are for newValue and oldValue? I didn't give them values, I just passed them in as parameters?

app.js 
angular.module('myApp', [])
.controller('myController', function ($scope, $http) {
  $scope.user = {name: 'Alex', id: 123};

  getUserData = function (id) {
    console.log('Getting user with ID: ' + id);
  }

$scope.$watch('user.id', function(newValue, oldValue){
      if (newValue) {
        api.getUserData($scope.user.id);
      }
    })

});
index.html 
<!DOCTYPE html>
<html ng-app="myApp">
<head>
  <title>Angular.js</title>
  <script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.3.2/angular.min.js"></script>
  <script src="app.js"></script>
</head>
<body ng-controller="myController">

  <input type="text" ng-model="user.id" />

</body>
</html>

1 Answer

Unsubscribed User
Unsubscribed User
501 Points
Unsubscribed User
Unsubscribed User
501 Points

I think the problem is that you want to observe ($watch) the id in the user object. As per the documentation writes, if you want to do a "deep" $watch, so you want to use the callback if any key has changed on the object, you have to use the $wath as per below:

$scope.$watch('user.id', function (newVal, oldVal) { /* Some code here */ }, true);

Please note the third argument!