Service in AngularJS

29 / Jun / 2014 by Amit Kumar 0 comments

When we are working on MVC (or MVVM for AngularJS) Design-Patterns, our application is loosely coupled because of different independent components defined for e.g. Controller, View, Services, Modal/Data etc. All the components have their own work/role but today we will discuss only Services.

Services are that part of application where we write our business logic and load data (if it is frond-end framework Service e.g. AngularJS Service then it loads data from Web Server and if it is back-end framework Service e.g. NodeJS Service then it loads data from Database Server or other Web Server). AngularJS also provides many built-in services e.g. $http, $q etc. $http is very commonly used service which helps us to load data from Web Server, we can hit Ajax request with the help of $http service, which internally hits XMLHTTPRequest.

Generally, instead of writing Services we do data loading from Web-Server in Controllers, which is obviously a bad practice. So lets try a basic program, where we will load data from Web-Server with the help of Service instead of writing the code into Controller.

var serviceTestApp = angular.module('serviceTest', []);

/*
 * Defining TestService, Which will load User list Asynchronously(From Web-Server).
 * for demo purpose we are using setTimeout().
 *
 * $q is built-in Angular Service which helps us to implement Promise-Defer Design Pattern and
 * will be injected to TestService by AngularJS via DI(Dependency Injection) Design Pattern.
 * */
serviceTestApp.service('TestService', function ($q) {
    // Defining Service function: getUsers which will load user list
    this.getUsers = function () {
        var deferred = $q.defer();
        setTimeout(function () {
            var users = [
                {name: "Amit Thakkar", age: 25},
                {name: "Namita", age: 36},
                {name: "Kanika", age: 43}
            ];
            deferred.resolve(users);
        }, 2000);
        return deferred.promise;
    };
});

Also, Services must be registered with module(Same as directives) via module.service API, in which first argument is the name of the Service and second argument is the function. Second argument function is just a constructor function that will be called with ‘new’ keyword by AngularJS itself. And this Service will be injected to Controllers or other Services (AngularJS also implement Dependency Injection Design Pattern to inject services to Controllers and Services).

/*
 * Defining TestController, who will use TestService to get User List.
 * */
function TestController($scope, TestService) {
    // Calling getUsers function on TestService.
    TestService.getUsers().
        then(function (users) {
            $scope.users = users;
        });
}

AngularJS Services implement Singleton Design Pattern so only one object is created for an application.

NOTE: You can checkout full working source code from this link.

Amit Kumar
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