AngularJS: Understanding the 'controller as' syntax and the importance of $watch

Question

AngularJS: Understanding the 'controller as' syntax and the importance of $watch

Is it possible to subscribe to property changes when using the controller as syntax?

controller('TestCtrl', function ($scope) {
  this.name = 'Max';
  this.changeName = function () {
    this.name = new Date();
  }
  // not working       
  $scope.$watch("name",function(value){
    console.log(value)
  });
});

<div ng-controller="TestCtrl as test">
  <input type="text" ng-model="test.name" />
  <a ng-click="test.changeName()" href="#">Change Name</a>
</div>

javascript angularjs angularjs-scope ng-controller

Answer 1

Answer №1

Simply connect the appropriate context.

$scope.$watch(angular.bind(this, function () {
  return this.name;
}), function (newVal) {
  console.log('Name changed to ' + newVal);
});

Check out this example: http://jsbin.com/yinadoce/1/edit

LATEST UPDATE:

I must say that Bogdan Gersak's response is quite similar; both suggestions focus on correctly binding this with the relevant context. However, I personally find his solution more elegant.

That being said, it is important to grasp the fundamental concept behind this process.

SECOND UPDATE:

For those using ES6, you can achieve the desired context by utilizing an arrow function.

$scope.$watch(() => this.name, function (newVal) {
  console.log('Name changed to ' + newVal);
});

See this example for a better understanding.

Answer 2

Simply connect the appropriate context.

$scope.$watch(angular.bind(this, function () {
  return this.name;
}), function (newVal) {
  console.log('Name changed to ' + newVal);
});

Check out this example: http://jsbin.com/yinadoce/1/edit

LATEST UPDATE:

I must say that Bogdan Gersak's response is quite similar; both suggestions focus on correctly binding this with the relevant context. However, I personally find his solution more elegant.

That being said, it is important to grasp the fundamental concept behind this process.

SECOND UPDATE:

For those using ES6, you can achieve the desired context by utilizing an arrow function.

$scope.$watch(() => this.name, function (newVal) {
  console.log('Name changed to ' + newVal);
});

See this example for a better understanding.

Answer 3

Answer №2

My typical approach is as follows:

controller('ExampleCtrl', function ($scope) {
    var vm = this;

    this.title = 'John';
    this.changeTitle = function () {
        this.title = new Date();
   }

   $scope.$watch(function () {
       return vm.title;
   },function(value){
        console.log(value)
   });
});

Answer 4

My typical approach is as follows:

controller('ExampleCtrl', function ($scope) {
    var vm = this;

    this.title = 'John';
    this.changeTitle = function () {
        this.title = new Date();
   }

   $scope.$watch(function () {
       return vm.title;
   },function(value){
        console.log(value)
   });
});

Answer 5

Answer №3

Here is an example of how you can achieve this:

   $scope.$watch("test.name",function(value){
        console.log(value)
   });

Check out the demo on JSFiddle to see it in action.

Answer 6

Here is an example of how you can achieve this:

   $scope.$watch("test.name",function(value){
        console.log(value)
   });

Check out the demo on JSFiddle to see it in action.

Answer 7

Answer №4

Instead of relying on the "test" from "TestCtrl as test" method mentioned in another response, you have the option to assign "self" as your scope:

controller('TestCtrl', function($scope){
    var self = this;
    $scope.self = self;

    self.name = 'john';
    self.updateName = function(){
            self.name = new Date();
        }

    $scope.$watch("self.name",function(value){
            console.log(value)
        });
})

This approach allows you to avoid being limited by the name defined in the DOM ("TestCtrl as test"), and eliminates the necessity to .bind(this) to a function.

...which can be utilized with the original html markup provided:

<div ng-controller="TestCtrl as test">
    <input type="text" ng-model="test.name" />
    <a ng-click="test.updateName()" href="#">Update Name</a>
</div>

Answer 8

Instead of relying on the "test" from "TestCtrl as test" method mentioned in another response, you have the option to assign "self" as your scope:

controller('TestCtrl', function($scope){
    var self = this;
    $scope.self = self;

    self.name = 'john';
    self.updateName = function(){
            self.name = new Date();
        }

    $scope.$watch("self.name",function(value){
            console.log(value)
        });
})

This approach allows you to avoid being limited by the name defined in the DOM ("TestCtrl as test"), and eliminates the necessity to .bind(this) to a function.

...which can be utilized with the original html markup provided:

<div ng-controller="TestCtrl as test">
    <input type="text" ng-model="test.name" />
    <a ng-click="test.updateName()" href="#">Update Name</a>
</div>

Answer 9

Answer №5

In AngularJs 1.5, the default $ctrl is used for implementing the ControllerAs structure.

$scope.$watch("$ctrl.name", (newValue) => {
    console.log(newValue)
});

Answer 10

In AngularJs 1.5, the default $ctrl is used for implementing the ControllerAs structure.

$scope.$watch("$ctrl.name", (newValue) => {
    console.log(newValue)
});

Answer 11

Answer №6

Here's a cool trick you can do with AngularJS: passing a function as the first argument of $watch():

 app.controller('TestCtrl', function ($scope) {
 this.name = 'Max';

// Check out this function
 $scope.$watch(function () {}, function (value){ console.log(value) });
 });

This means we can reference our `this.name` property:

app.controller('TestCtrl', function ($scope) {
    this.name = 'Max';

    // This is awesome
    $scope.$watch(angular.bind(this, function () {
    return this.name; // Accessing the `this` context from above!!
    }), function (value) {
      console.log(value);
    });
});

If you want to learn more about the controllerAs syntax in AngularJS, check out this informative post.

Answer 12

Here's a cool trick you can do with AngularJS: passing a function as the first argument of $watch():

 app.controller('TestCtrl', function ($scope) {
 this.name = 'Max';

// Check out this function
 $scope.$watch(function () {}, function (value){ console.log(value) });
 });

This means we can reference our `this.name` property:

app.controller('TestCtrl', function ($scope) {
    this.name = 'Max';

    // This is awesome
    $scope.$watch(angular.bind(this, function () {
    return this.name; // Accessing the `this` context from above!!
    }), function (value) {
      console.log(value);
    });
});

If you want to learn more about the controllerAs syntax in AngularJS, check out this informative post.

Answer 13

Answer №7

One suggestion is to utilize the $onChanges angular component lifecycle method.

For more information, refer to the documentation at: https://docs.angularjs.org/guide/component specifically in the Component-based application section

Answer 14

One suggestion is to utilize the $onChanges angular component lifecycle method.

For more information, refer to the documentation at: https://docs.angularjs.org/guide/component specifically in the Component-based application section

Answer 15

Answer №8

Implementing a $watch feature in ES6 format posed a challenge that I had not anticipated. Here's the solution:

// Assuming
// controllerAs: "ctrl"
// or
// ng-controller="MyCtrl as ctrl"
export class MyCtrl {
  constructor ($scope) {
    'ngInject';
    this.foo = 10;
    // Option 1
    $scope.$watch('ctrl.foo', this.watchChanges());
    // Option 2
    $scope.$watch(() => this.foo, this.watchChanges());
  }

  watchChanges() {
    return (newValue, oldValue) => {
      console.log('new', newValue);
    }
  }
}

Answer 16

Implementing a $watch feature in ES6 format posed a challenge that I had not anticipated. Here's the solution:

// Assuming
// controllerAs: "ctrl"
// or
// ng-controller="MyCtrl as ctrl"
export class MyCtrl {
  constructor ($scope) {
    'ngInject';
    this.foo = 10;
    // Option 1
    $scope.$watch('ctrl.foo', this.watchChanges());
    // Option 2
    $scope.$watch(() => this.foo, this.watchChanges());
  }

  watchChanges() {
    return (newValue, oldValue) => {
      console.log('new', newValue);
    }
  }
}

Answer 17

Answer №9

REMINDER: This method may not function properly if the View and Controller are intertwined within a route or directive definition object. The following solution is effective only when "SomeController as SomeCtrl" is specified in the HTML. As pointed out by Mark V. in the comment below, it's advisable to follow the approach suggested by Bogdan.

In my implementation, I start the controller with var vm = this; to avoid any confusion with the keyword "this." Then, I assign vm.name = 'Max';, and in the watch function, I use return vm.name. Similar to @Bogdan's usage of "self," I utilize "vm" for consistency. This variable, whether named "vm" or "self," is necessary because the context of "this" changes within the function (thus, returning this.name wouldn't be effective). Additionally, remember to inject $scope in your elegant "controller as" solution to access $watch. For further guidance, refer to John Papa's Style Guide: https://github.com/johnpapa/angularjs-styleguide#controllers

function SomeController($scope, $log) {
    var vm = this;
    vm.name = 'Max';

    $scope.$watch('vm.name', function(current, original) {
        $log.info('vm.name was %s', original);
        $log.info('vm.name is now %s', current);
    });
}

Answer 18

REMINDER: This method may not function properly if the View and Controller are intertwined within a route or directive definition object. The following solution is effective only when "SomeController as SomeCtrl" is specified in the HTML. As pointed out by Mark V. in the comment below, it's advisable to follow the approach suggested by Bogdan.

In my implementation, I start the controller with var vm = this; to avoid any confusion with the keyword "this." Then, I assign vm.name = 'Max';, and in the watch function, I use return vm.name. Similar to @Bogdan's usage of "self," I utilize "vm" for consistency. This variable, whether named "vm" or "self," is necessary because the context of "this" changes within the function (thus, returning this.name wouldn't be effective). Additionally, remember to inject $scope in your elegant "controller as" solution to access $watch. For further guidance, refer to John Papa's Style Guide: https://github.com/johnpapa/angularjs-styleguide#controllers

function SomeController($scope, $log) {
    var vm = this;
    vm.name = 'Max';

    $scope.$watch('vm.name', function(current, original) {
        $log.info('vm.name was %s', original);
        $log.info('vm.name is now %s', current);
    });
}

Answer 19

Answer №10

Learn how to implement this technique without using $scope and $watch by checking out the article on Avoiding Common Mistakes in AngularJS

When utilizing the "controller as" syntax, it is recommended to refrain from relying on $scope for cleaner code.

You can view a demonstration of this approach in action on JSFiddle. (A service is used to manage the name value to prevent stack overflow caused by ES5 Object.defineProperty's set and get methods.)

var app = angular.module('my-module', []);

app.factory('testService', function() {
    var name = 'Max';

    var getName = function() {
        return name;
    }

    var setName = function(val) {
        name = val;
    }

    return {getName:getName, setName:setName};
});

app.controller('TestCtrl', function (testService) {
    var vm = this;

    vm.changeName = function () {
        vm.name = new Date();
    }

    Object.defineProperty(this, "name", {
        enumerable: true,
        configurable: false,
        get: function() {
            return testService.getName();
        },
        set: function (val) {
            testService.setName(val);
            console.log(vm.name);
        }
    }); 
});

Answer 20

Learn how to implement this technique without using $scope and $watch by checking out the article on Avoiding Common Mistakes in AngularJS

When utilizing the "controller as" syntax, it is recommended to refrain from relying on $scope for cleaner code.

You can view a demonstration of this approach in action on JSFiddle. (A service is used to manage the name value to prevent stack overflow caused by ES5 Object.defineProperty's set and get methods.)

var app = angular.module('my-module', []);

app.factory('testService', function() {
    var name = 'Max';

    var getName = function() {
        return name;
    }

    var setName = function(val) {
        name = val;
    }

    return {getName:getName, setName:setName};
});

app.controller('TestCtrl', function (testService) {
    var vm = this;

    vm.changeName = function () {
        vm.name = new Date();
    }

    Object.defineProperty(this, "name", {
        enumerable: true,
        configurable: false,
        get: function() {
            return testService.getName();
        },
        set: function (val) {
            testService.setName(val);
            console.log(vm.name);
        }
    }); 
});

AngularJS: Understanding the 'controller as' syntax and the importance of $watch

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

Answer №7

Answer №8

Answer №9

Answer №10

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