What is the purpose of setting a controller for your routes in AngularJS?

Question

What is the purpose of setting a controller for your routes in AngularJS?

Setting directives aside, controllers are often placed somewhere in the middle of a view to manipulate specific pieces of HTML with state or behavior. This can be done at any level, even at the highest level. The relationship between the view and controller is closely connected.

Why would you want to assign a controller at the route level as well? I have always found this concept puzzling. What is the underlying philosophy behind it? What benefits does assigning a controller outside of the view offer compared to placing it at the top of the view itself? It doesn't seem to be for swapping out controllers for different implementations; that is not a common practice.

/edit: Is it possible that assigning a controller at the route level is necessary for manual resolution that requires injection of dependencies? (Refer to John Papa's example)

javascript angularjs

Answer 1

Answer №1

There are many valid reasons to consider when deciding whether or not to define a controller for a route, but one major reason stands out. Imagine this scenario:

You have a template that you want to reuse with different routes/states
You may wish to assign a different controller to the template depending on the route.

If you use ng-controller in your template, you won't be able to easily reuse that template with a different controller.

By assigning the controller via the route, you gain more flexibility.

Conventional Approach

In this example, I will be using UI.Router as it is the framework I am most familiar with.

.state( 'users', {
    templateUrl: 'person.html'
    controller: 'UsersController'
})

.state( 'admin', {
    templateUrl: 'person.html'
    controller: 'AdminController'
})

Same template, different routes, with different controllers.

Dynamic Approach

It's not just about switching controllers for another implementation

I'm not going to debate the pros and cons of this approach, but I have used it myself and seen it discussed on forums and blogs.

.state( 'entity', {
    templateUrl: 'person.html'
    controller: function( ...injectables ){
        var UserController = function(){ ... }
        var AdminController = function(){ ... }

        var ControllerClass = isAdmin ? AdminController : UserController;
        return new ControllerClass()           
    }
})

Answer 2

There are many valid reasons to consider when deciding whether or not to define a controller for a route, but one major reason stands out. Imagine this scenario:

You have a template that you want to reuse with different routes/states
You may wish to assign a different controller to the template depending on the route.

If you use ng-controller in your template, you won't be able to easily reuse that template with a different controller.

By assigning the controller via the route, you gain more flexibility.

Conventional Approach

In this example, I will be using UI.Router as it is the framework I am most familiar with.

.state( 'users', {
    templateUrl: 'person.html'
    controller: 'UsersController'
})

.state( 'admin', {
    templateUrl: 'person.html'
    controller: 'AdminController'
})

Same template, different routes, with different controllers.

Dynamic Approach

It's not just about switching controllers for another implementation

I'm not going to debate the pros and cons of this approach, but I have used it myself and seen it discussed on forums and blogs.

.state( 'entity', {
    templateUrl: 'person.html'
    controller: function( ...injectables ){
        var UserController = function(){ ... }
        var AdminController = function(){ ... }

        var ControllerClass = isAdmin ? AdminController : UserController;
        return new ControllerClass()           
    }
})

What is the purpose of setting a controller for your routes in AngularJS?

Answer №1

Conventional Approach

Dynamic Approach

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