A controller is a basic structure used in Angular to preserve scope and handle certain actions within a page. Each controller is coupled with an HTML view.

Below is a basic boilerplate for an Angular app:

<!DOCTYPE html>

<html lang="en" ng-app='MyFirstApp'>
    <head>
        <title>My First App</title>

        <!-- angular source -->
        <script src="https://code.angularjs.org/1.5.3/angular.min.js"></script>

        <!-- Your custom controller code -->
        <script src="js/controllers.js"></script>
    </head>
    <body>
        <div ng-controller="MyController as mc">
            <h1>{ { mc.title } }</h1>
            <p>{ { mc.description } }</p>
            <button ng-click="mc.clicked()">
                Click Me!
            </button>
        </div>
    </body>
</html>

There are a few things to note here:

<html ng-app='MyFirstApp'>

Setting the app name with ng-app lets you access the application in an external Javascript file, which will be covered below.

<script src="js/controllers.js"></script>

We'll need a Javascript file where you define your controllers and their actions/data.

<div ng-controller="MyController as mc">

The ng-controller attribute sets the controller for that DOM element and all elements that are children (recursively) below it.

You can have multiple of the same controller (in this case, MyController) by saying ... as mc, we're giving this instance of the controller an alias.

<h1>{ { mc.title } }</h1>

The { { ... } } notation is an Angular expression. In this case, this will set the inner text of that <h1> element to whatever the value of mc.title is.

Note: Angular employs dual-way data binding, meaning that regardless of how you update the mc.title value, it will be reflected in both the controller and the page.

Also note that Angular expressions do not have to reference a controller. An Angular expression can be as simple as { { 1 + 2 } } or { { "Hello " + "World" } }.

<button ng-click="mc.clicked()">

ng-click is an Angular directive, in this case binding the click event for the button to trigger the clicked() function of the MyController instance.

With those things in mind, let's write an implementation of the MyController controller. With the example above, you would write this code in js/controller.js.

First, you'll need to instantiate the Angular app in your Javascript.

var app = angular.module("MyFirstApp", []);

Note that the name we pass here is the same as the name you set in your HTML with the ng-app directive.

Now that we have the app object, we can use that to create controllers.

app.controller("MyController", function() {
  var ctrl = this;

  ctrl.title = "My First Angular App";
  ctrl.description = "This is my first Angular app!";

  ctrl.clicked = function() {
    alert("MyController.clicked()");
  };
});

Note: For anything that we want to be a part of the controller instance, we use the this keyword.

This is all that is required to build a simple controller.

There are a couple different ways to protect your controller creation from minification.

The first is called inline array annotation. It looks like the following:

var app = angular.module("app");
app.controller("sampleController", [
  "$scope",
  "$http",
  function(a, b) {
    //logic here
  },
]);

The second parameter of the controller method can accept an array of dependencies. As you can see I've defined $scope and $http which should correspond to the parameters of the controller function in which a will be the $scope, and b would be $http. Take note that the last item in the array should be your controller function.

The second option is using the $inject property. It looks like the following:

var app = angular.module("app");
app.controller("sampleController", sampleController);
sampleController.$inject = ["$scope", "$http"];
function sampleController(a, b) {
  //logic here
}

This does the same thing as inline array annotation but provides a different styling for those that prefer one option over the other.

The order of injected dependencies is important

When injecting dependencies using the array form, be sure that the list of the dependencies match its corresponding list of arguments passed to the controller function.

Note that in the following example, $scope and $http are reversed. This will cause a problem in the code.

// Intentional Bug: injected dependencies are reversed which will cause a problem
app.controller("sampleController", [
  "$scope",
  "$http",
  function($http, $scope) {
    $http.get("sample.json");
  },
]);

In Angular $scope is the glue between the Controller and the View that helps with all of our data binding needs. Controller As is another way of binding controller and view and is mostly recommended to use. Basically these are the two controller constructs in Angular (i.e $scope and Controller As).

Different ways of using Controller As are -

controllerAs View Syntax

<div ng-controller="CustomerController as customer">
    { { customer.name } }
</div>

controllerAs Controller Syntax

function CustomerController() {
  this.name = {};
  this.sendMessage = function() {};
}

controllerAs with vm

function CustomerController() {
  /*jshint validthis: true */
  var vm = this;
  vm.name = {};
  vm.sendMessage = function() {};
}

controllerAs is syntactic sugar over $scope. You can still bind to the View and still access $scope methods. Using controllerAs, is one of the best practices suggested by the angular core team. There are many reason for this, few of them are -

NOTE: using controllerAs syntax add to current scope reference to current controller, so it available as field

<div ng-controller="Controller as vm>...</div>

vm is available as $scope.vm.

To create minification-safe angular controllers, you will change the controller function parameters.

The second argument in the module.controller function should be passed an array, where the last parameter is the controller function, and every parameter before that is the name of each injected value.

This is different from the normal paradigm; that takes the controller function with the injected arguments.

Given:

var app = angular.module("myApp");

The controller should look like this:

app.controller("ctrlInject", [
  /* Injected Parameters */
  "$Injectable1",
  "$Injectable2",
  /* Controller Function */
  function($injectable1Instance, $injectable2Instance) {
    /* Controller Content */
  },
]);

Note: The names of injected parameters are not required to match, but they will be bound in order.

This will minify to something similar to this:

var a = angular.module("myApp");
a.controller("ctrlInject", [
  "$Injectable1",
  "$Injectable2",
  function(b, c) {
    /* Controller Content */
  },
]);

The minification process will replace every instance of app with a, every instance of $Injectable1Instance with b, and every instance of $Injectable2Instance with c.

angular.module("app").controller("SampleController", SampleController);

SampleController.$inject = ["$log", "$scope"];
function SampleController($log, $scope) {
  $log.debug("*****SampleController******");

  /* Your code below */
}

Note: The .$inject will make sure your dependencies doesn't get scrambled after minification. Also, make sure it's in order with the named function.

Nesting controllers chains the $scope as well. Changing a $scope variable in the nested controller changes the same $scope variable in the parent controller.

.controller('parentController', function ($scope) {
    $scope.parentVariable = "I'm the parent";
});

.controller('childController', function ($scope) {
    $scope.childVariable = "I'm the child";

    $scope.childFunction = function () {
        $scope.parentVariable = "I'm overriding you";
    };
});

Now let's try to handle both of them, nested.

<body ng-controller="parentController">
  What controller am I? {{ parentVariable }}
  <div ng-controller="childController">
    What controller am I? {{ childVariable }}
    <button ng-click="childFunction()"> Click me to override! </button>
  </div>
</body>

Nesting controllers may have it's benefits, but one thing must be kept in mind when doing so. Calling the ngController directive creates a new instance of the controller - which can often create confusion and unexpected results.

Syntax

• <htmlElement ng-controller="controllerName"> ... </htmlElement>
• app.controller('controllerName', controllerFunction);