What are the implications of declaring a controller as a variable within itself or utilizing $scope?

Question

What are the implications of declaring a controller as a variable within itself or utilizing $scope?

As I dive into learning and utilizing AngularJS, certain concepts still remain unclear to me.

Here is my query: within my application, there is a controller that utilizes $http to fetch data from the backend upon initialization. Following a comprehensive tutorial from CodeSchool on Angular, I implemented the following structure:

app.controller("agentController", function ($http) {
    var agentsCtrl = this;
    agentsCtrl.agents = [];
    $http.get("getAgents").success(function (data) {
        agentsCtrl.agents = data;
    });
...

HTML:

<div ng-controller="agentController as agentCtrl">
    <div ng-repeat="agent in agentCtrl.agents">
...

This setup works well, but I question the necessity of declaring the controller as a variable within itself using this. My understanding leads me to believe it's required so that I can reference it correctly within the $http service, where the this keyword would otherwise return an incorrect scope. Is my interpretation accurate?

I also discovered another approach which functions similarly:

app.controller("agentController", function ($http, $scope) {
    $scope.agents = [];
    $http.get("getAgents").success(function (data) {
        $scope.agents = data;
    });

HTML:

<div ng-controller="agentController as agentCtrl">
    <div ng-repeat="agent in agents">
...

This alternative method appears to work because I explicitly inject the scope and use it within the service. Additionally, the HTML structure slightly differs. In the initial case, calling agentCtrl.agents is necessary, while with scope, simply agents suffices. This change stems from the fact that the variable is now declared on the scope rather than the controller. Is this assumption correct?

What would be considered best practice when encountering similar scenarios?

Your insights are greatly appreciated!

javascript angularjs

Answer 1

Answer №1

Are you considering two different approaches - "Controller as" or "$scope"?

$scope

The traditional use of scope binding would be:

<div ng-controller="MainController">  
  {{ someObj.someProp }}
</div>

app.controller('MainController', function ($scope) {  
  $scope.someObj = {
    someProp: 'Some value.'
  };
});

"Controller as"

With this technique, you can bind as follows:

<div ng-controller="MainController as main">  
  {{ main.someProp }}
</div>

app.controller('MainController', function () {  
  this.someProp = 'Some value.'
});

Both methods are effective and have their benefits. The main difference lies in personal preference.

However, the majority of the community leans towards 'Controller as' - but why?

Readability - Easily identify which model in the scope is bound to a DOM element
Testability - Testing code becomes slightly simpler without needing to inject $scope
Alignment with Angular 2.0 vision where controllers act more like constructor functions than adding elements to $scope

Answer 2

Are you considering two different approaches - "Controller as" or "$scope"?

$scope

The traditional use of scope binding would be:

<div ng-controller="MainController">  
  {{ someObj.someProp }}
</div>

app.controller('MainController', function ($scope) {  
  $scope.someObj = {
    someProp: 'Some value.'
  };
});

"Controller as"

With this technique, you can bind as follows:

<div ng-controller="MainController as main">  
  {{ main.someProp }}
</div>

app.controller('MainController', function () {  
  this.someProp = 'Some value.'
});

Both methods are effective and have their benefits. The main difference lies in personal preference.

However, the majority of the community leans towards 'Controller as' - but why?

Readability - Easily identify which model in the scope is bound to a DOM element
Testability - Testing code becomes slightly simpler without needing to inject $scope
Alignment with Angular 2.0 vision where controllers act more like constructor functions than adding elements to $scope

Answer 3

Answer №2

Question 1:

To ensure the correct reference to scope, it is necessary to save it using var agentsCtrl = this. This is crucial because an anonymous function is being created to serve as a callback. Failure to do so will result in the context variable (this) becoming window.

app.controller("agentController", function ($http) {
    // this == your controller
    var agentsCtrl = this;

    $http.get("getAgents").success(function (data) {
        // Anonymous function 
        // this == Window Object
    });
});

Question 2:

$scope acts as the connector between the application controller and the view. It can be referenced as a global variable that provides access from both the view and the controllers.

$scope.agents = []; // From controller

And

{{ agents }} // From view (no need to specify the $scope variable)

I personally prefer assigning an alias to the controller and utilizing it in my HTML, similar to what you have done with

<div ng-controller="agentController as agentCtrl">
    <div ng-repeat="agent in agents">
...

Both approaches are valid and will yield the desired results.

Answer 4

Question 1:

To ensure the correct reference to scope, it is necessary to save it using var agentsCtrl = this. This is crucial because an anonymous function is being created to serve as a callback. Failure to do so will result in the context variable (this) becoming window.

app.controller("agentController", function ($http) {
    // this == your controller
    var agentsCtrl = this;

    $http.get("getAgents").success(function (data) {
        // Anonymous function 
        // this == Window Object
    });
});

Question 2:

$scope acts as the connector between the application controller and the view. It can be referenced as a global variable that provides access from both the view and the controllers.

$scope.agents = []; // From controller

And

{{ agents }} // From view (no need to specify the $scope variable)

I personally prefer assigning an alias to the controller and utilizing it in my HTML, similar to what you have done with

<div ng-controller="agentController as agentCtrl">
    <div ng-repeat="agent in agents">
...

Both approaches are valid and will yield the desired results.

Answer 5

Answer №3

The keyword 'this' is dynamic and can have a different context when used within a function in a controller. Avoiding this issue by capturing the correct context of 'this' is important.

For example:

app.controller('MainCtrl', function() {
  this.test = 'test';

  angular.forEach(testArray, function (item) {
    console.debug(this.test);
  });
});

In this case, 'this.test' is undefined due to the change in scope of 'this'.

Plunkr

To solve this issue, use a variable:

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

  vm.test = 'test';
  var testArray = [
    1, 2, 3, 4
  ];

  angular.forEach(testArray, function (item) {
    console.debug(vm.test);
  });
});

Plunkr

This information was referenced from John Papa's AngularJS Style Guide

Answer 6

The keyword 'this' is dynamic and can have a different context when used within a function in a controller. Avoiding this issue by capturing the correct context of 'this' is important.

For example:

app.controller('MainCtrl', function() {
  this.test = 'test';

  angular.forEach(testArray, function (item) {
    console.debug(this.test);
  });
});

In this case, 'this.test' is undefined due to the change in scope of 'this'.

Plunkr

To solve this issue, use a variable:

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

  vm.test = 'test';
  var testArray = [
    1, 2, 3, 4
  ];

  angular.forEach(testArray, function (item) {
    console.debug(vm.test);
  });
});

Plunkr

This information was referenced from John Papa's AngularJS Style Guide

Answer 7

Answer №4

Responding to your inquiry regarding Ben Diamant's response.

The usage of the less conventional alias syntax (as Alias) can streamline your code, making it more comprehensible for anyone reviewing it.

As per the ng-controller spec:

Implementing controller as

clearly indicates which controller is being accessed in the template when multiple controllers are involved in an element.

If you structure your controllers as classes, it provides easier access to properties and methods within the controller code that will appear on the scope.

Since there is always a . in the bindings, concerns about prototypal inheritance masking primitives are eliminated.

Be sure to also explore this useful explanation highlighting the benefits of using alias syntax: Link.

One of the key advantages of alias syntax is its ability to allow you to

reference the desired controller without getting bogged down by the complexities of scope inheritance.

I trust this clarifies things for you.

Answer 8

Responding to your inquiry regarding Ben Diamant's response.

The usage of the less conventional alias syntax (as Alias) can streamline your code, making it more comprehensible for anyone reviewing it.

As per the ng-controller spec:

Implementing controller as

clearly indicates which controller is being accessed in the template when multiple controllers are involved in an element.

If you structure your controllers as classes, it provides easier access to properties and methods within the controller code that will appear on the scope.

Since there is always a . in the bindings, concerns about prototypal inheritance masking primitives are eliminated.

Be sure to also explore this useful explanation highlighting the benefits of using alias syntax: Link.

One of the key advantages of alias syntax is its ability to allow you to

reference the desired controller without getting bogged down by the complexities of scope inheritance.

I trust this clarifies things for you.

What are the implications of declaring a controller as a variable within itself or utilizing $scope?

Answer №1

$scope

"Controller as"

Answer №2

Answer №3

Answer №4

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