AngularJS Uses and significance


Example

These events can be used to communicate between 2 or more controllers.

$emit dispatches an event upwards through the scope hierarchy, while $broadcast dispatches an event downwards to all child scopes.This has been beautifully explained here.

There can be basically two types of scenario while communicating among controllers:


  1. When controllers have Parent-Child relationship. (we can mostly use $scope in such scenarios)

  1. When controllers are not independent to each other and are needed to be informed about each others activity. (we can use $rootScope in such scenarios)

eg: For any ecommerce website, suppose we have ProductListController(which controls the product listing page when any product brand is clicked ) and CartController (to manage cart items) . Now, when we click on Add to Cart button , it has to be informed to CartController as well, so that it can reflect new cart item count/details in the navigation bar of the website. This can be achieved using $rootScope.


With $scope.$emit

<html>
  <head>
    <script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.4.4/angular.js"></script>
    <script>
        var app = angular.module('app', []);

        app.controller("FirstController", function ($scope) {
            $scope.$on('eventName', function (event, args) {
                $scope.message = args.message;
            });
        });

        app.controller("SecondController", function ($scope) {
            $scope.handleClick = function (msg) {
                $scope.$emit('eventName', {message: msg});
            };
        });

    </script>
  </head>
  <body ng-app="app">
    <div ng-controller="FirstController" style="border:2px ;padding:5px;">
        <h1>Parent Controller</h1>
        <p>Emit Message : {{message}}</p>
        <br />
        <div ng-controller="SecondController" style="border:2px;padding:5px;">
            <h1>Child Controller</h1>
            <input ng-model="msg">
            <button ng-click="handleClick(msg);">Emit</button>
        </div>
    </div>
  </body>
</html>

With $scope.$broadcast:

<html>
  <head>
    <title>Broadcasting</title>
    <script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.4.4/angular.js"></script>
    <script>
        var app = angular.module('app', []);

        app.controller("FirstController", function ($scope) {
            $scope.handleClick = function (msg) {
                $scope.$broadcast('eventName', {message: msg});
            };

        });

        app.controller("SecondController", function ($scope) {
            $scope.$on('eventName', function (event, args) {
                $scope.message = args.message;
            });
        });

    </script>
  </head>
  <body ng-app="app">
    <div ng-controller="FirstController" style="border:2px solid ; padding:5px;">
        <h1>Parent Controller</h1>
        <input ng-model="msg">
        <button ng-click="handleClick(msg);">Broadcast</button>
        <br /><br />
        <div ng-controller="SecondController" style="border:2px solid ;padding:5px;">
            <h1>Child Controller</h1>
            <p>Broadcast Message : {{message}}</p>
        </div>
    </div>
  </body>
</html>