AngularJS Service / Factory Tutorial with Example

angularjs service

1. Introduction to AngularJS Services

In AngularJS world, the services are singleton objects or functions that carry out specific tasks. It holds some business logic. Separation of concern is at the heart while designing an AngularJS application. Your controller must be responsible for binding model data to views using $scope. It does not contain logic to fetch the data or manipulating it.

For that we must create singleton objects called services. AngularJS can manage these service objects. Wherever we want to use the service, we just have to specify its name and AngularJS auto-magically inject these objects (more on this later).

Thus service is a stateless object that contains some useful functions. These functions can be called from anywhere; Controllers, Directive, Filters etc. Thus we can divide our application in logical units. The business logic or logic to call HTTP url to fetch data from server can be put within a service object.

Putting business and other logic within services has many advantages. First it fulfills the principle of separation of concern or segregation of duties. Each component is responsible for its own work making application more manageable. Second this way each component can be more testable. AngularJS provides first class support for unit testing. Thus we can quickly write tests for our services making them robust and less error prone.

angularjs service diagram

Consider above diagram. Here we divide our application in two controllers: 1. Profile and 2. Dashboard. Each of these controllers require certain user data from server. Thus instead of repeating the logic to fetch data from server in each controller, we create a User service which hides the complexity. AngularJS automatically inject User service in both Profile and Dashboard controller. Thus our application becomes for modular and testable.

2. AngularJS internal services

AngularJS internally provides many services that we can use in our application. $http is one example (Note: All angularjs internal services starts with $ sign). There are other useful services such as $route, $window, $location etc.

These services can be used within any Controller by just declaring them as dependencies. For example:

module.controller('FooController', function($http){
	//...
});

module.controller('BarController', function($window){
	//...
});

3. AngularJS custom services

We can define our own custom services in angular js app and use them wherever required.

There are several ways to declare angularjs service within application. Following are two simple ways:

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

module.service('userService', function(){
	this.users = ['John', 'James', 'Jake'];
});

or we can use factory method

module.factory('userService', function(){
	
	var fac = {};
	
	fac.users = ['John', 'James', 'Jake']; 
	
	return fac;

});

Both of the ways of defining a service function/object are valid. We will shortly see the difference between factory() and service() method. For now just keep in mind that both these apis defines a singleton service object that can be used within any controller, filter, directive etc.

4. AngularJS Service vs Factory

AngularJS services as already seen earlier are singleton objects. These objects are application wide. Thus a service object once created can be used within any other services or controllers etc.

We saw there are two ways (actually four, but for sake of simplicity lets focus on 2 ways that are widely used) of defining an angularjs service. Using module.factory and module.service.

module.service( 'serviceName', function );

module.factory( 'factoryName', function );

When declaring serviceName as an injectable argument you will be provided with an instance of the function. In other words new FunctionYouPassedToService(). This object instance becomes the service object that AngularJS registers and injects later to other services / controllers if required.

When declaring factoryName as an injectable argument you will be provided with the value that is returned by invoking the function reference passed to module.factory.

In below example we define MyService in two different ways. Note how in .service we create service methods using this.methodname. In .factory we created a factory object and assigned the methods to it.

AngularJS .service

module.service('MyService', function() {
	this.method1 = function() {
			//..
		}

	this.method2 = function() {
			//..
		}
});

AngularJS .factory

module.factory('MyService', function() {
	
	var factory = {}; 

	factory.method1 = function() {
			//..
		}

	factory.method2 = function() {
			//..
		}

	return factory;
});

5. Injecting dependencies in services

Angularjs provides out of the box support for dependency management.

In general the wikipedia definition of dependency injection is:

Dependency injection is a software design pattern that allows the removal of hard-coded dependencies and makes it possible to change them, whether at run-time or compile-time. …

We already saw in previous tutorials how to use angularjs dependency management and inject dependencies in controllers. We injected $scope object in our controller class.

Dependency injection mainly reduces the tight coupling of code and create modular code that is more maintainable and testable. AngularJS services are the objects that can be injected in any other Angular construct (like controller, filter, directive etc). You can define a service which does certain tasks and inject it wherever you want. In that way you are sure your tested service code works without any glitch.

Like it is possible to inject service object into other angular constructs, you can also inject other objects into service object. One service might be dependence on another.

Let us consider an example where we use dependency injection between different services and controller. For this demo let us create a small calculator app that does two things: squares and cubes. We will create following entities in AngularJS:

  1. MathService – A simple custom angular service that has 4 methods: add, subtract, multiply and divide. We will only use multiply in our example.
  2. CalculatorService – A simple custom angular service that has 2 methods: square and cube. This service has dependency on MathService and it uses MathService.multiply method to do its work.
  3. CalculatorController – This is a simple controller that handler user interactions. For UI we have one textbox to take a number from user and two buttons; one to square another to multiply.

Below is the code:

5.1 The HTML

Enter a number:
Answer: {{answer}}

5.2 The JavaScript

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

app.service('MathService', function() {
    this.add = function(a, b) { return a + b };
    
    this.subtract = function(a, b) { return a - b };
    
    this.multiply = function(a, b) { return a * b };
    
    this.divide = function(a, b) { return a / b };
});

app.service('CalculatorService', function(MathService){
    
    this.square = function(a) { return MathService.multiply(a,a); };
    this.cube = function(a) { return MathService.multiply(a, MathService.multiply(a,a)); };

});

app.controller('CalculatorController', function($scope, CalculatorService) {

    $scope.doSquare = function() {
        $scope.answer = CalculatorService.square($scope.number);
    }

    $scope.doCube = function() {
        $scope.answer = CalculatorService.cube($scope.number);
    }
});

5.3 Online Demo

Thus in the above angularjs injected service object to another service and in turn injected final service object to the controller object. You can inject same service object in multiple controllers. As angularjs service object is inheritedly singleton. Thus only one service object will be created per application.

6. End to End application using AngularJS Service

Let us apply the knowledge that we acquired so far and create a ContactManager application. This is the same app that we built-in our last tutorial. We will add a service to it and see how we can divide the code between service and controllers. Following are some basic requirements of this application:

  1. User can add new contact (name, email address and phone number)
  2. List of contacts should be shown
  3. User can delete any contact from contact list
  4. User can edit any contact from contact list

Following is the HTML code which defines a FORM to save new contact and edit contact. And also it defines a table where contacts can be viewed.

6.1 The HTML


Name Email Phone Action
{{ contact.name }} {{ contact.email }} {{ contact.phone }} edit | delete

Next we add the AngularJS code to and life to our ContactManager appllication. We define a module ‘app’. This module is then used to create Service and Controller.

See in below code how ContactService is created. It has simple methods to save/delete/get the contact.

Note how the service object in injected in controller.

6.2 The JavaScript


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

module.service('ContactService', function () {
    //to create unique contact id
    var uid = 1;
    
    //contacts array to hold list of all contacts
    var contacts = [{
        id: 0,
        'name': 'Viral',
            'email': 'hello@gmail.com',
            'phone': '123-2343-44'
    }];
    
    //save method create a new contact if not already exists
    //else update the existing object
    this.save = function (contact) {
        if (contact.id == null) {
            //if this is new contact, add it in contacts array
            contact.id = uid++;
            contacts.push(contact);
        } else {
            //for existing contact, find this contact using id
            //and update it.
            for (i in contacts) {
                if (contacts[i].id == contact.id) {
                    contacts[i] = contact;
                }
            }
        }

    }

    //simply search contacts list for given id
    //and returns the contact object if found
    this.get = function (id) {
        for (i in contacts) {
            if (contacts[i].id == id) {
                return contacts[i];
            }
        }

    }
    
    //iterate through contacts list and delete 
    //contact if found
    this.delete = function (id) {
        for (i in contacts) {
            if (contacts[i].id == id) {
                contacts.splice(i, 1);
            }
        }
    }

    //simply returns the contacts list
    this.list = function () {
        return contacts;
    }
});

module.controller('ContactController', function ($scope, ContactService) {

    $scope.contacts = ContactService.list();

    $scope.saveContact = function () {
        ContactService.save($scope.newcontact);
        $scope.newcontact = {};
    }


    $scope.delete = function (id) {

        ContactService.delete(id);
        if ($scope.newcontact.id == id) $scope.newcontact = {};
    }


    $scope.edit = function (id) {
        $scope.newcontact = angular.copy(ContactService.get(id));
    }
})

6.3 Online Demo

That’s All Folks

We saw that angularjs service/factory objects are. How to define our own custom service/factory object in angularjs. Also we saw how dependency injection works. In the end we created a simply calculator application that wrap up all the concepts.

I hope you liked this tutorial. Feel free to post your comment below.

In this ongoing series, I will try to publish more AngularJS articles on topics like angularjs $http service, AngularJS filters, AngularJS directives etc.

References



96 Comments

  • A.Lepe 27 October, 2014, 14:20

    Your tutorials on AngularJS helped me to startup with it (looking forward for more of this serie!). I wish they were included on the AngularJs website as they are very clear and easy to follow. Thanks!

  • Amruth 2 November, 2014, 8:21

    Thanks Buddy for the great tutorial, it was very helpful for beginner like me.You have pointed the things in a very understandable manner.

  • trendrumah 14 November, 2014, 12:21

    it helped me, understandable
    Thanks

  • JSolo 18 November, 2014, 6:07

    Wonderful stuff! Was able to connect to SQL server db via express.js to serve up nice rest api and get some nice UI going

    Thanks so much!!!

  • Anup kumar 4 December, 2014, 14:10

    I am also trying to call a method of one service into the other service but it is giving error saying
    Cannot read property ‘create’ of undefined

    Java script code here [/code javascript]

    app.service(‘CookieService’, [‘$cookies’,
    function ($cookies) {
    this.create = function (token, userName) {
    $cookies.token = token;
    $cookies.name = userName;
    };
    return this;
    }]);

    app.service(‘AuthService’,
    function (CookieService) {
    return {
    login: function (credentials) {
    CookieService.create(token,username);
    }
    };
    });

    Please ignore syntax error if it is there

  • Al 10 December, 2014, 3:50

    We needed an example of using a factory. Please work on your english. Thanks.

  • Syed Shaik shavali 16 December, 2014, 17:26

    Thanks..Good article.

  • Jason Maggard 22 December, 2014, 5:07

    Thanks a million. Very well explained and easy to follow. Very much appreciated.

  • Ankit 30 December, 2014, 15:50

    Well explained article ,thanks a lot for your blog.

  • rick 7 January, 2015, 23:54

    Great example Viral, (and your English is just fine). Thank you.

  • Martin 9 January, 2015, 2:56

    One of the best tutorials I have used in a long time. Well done. Perhaps a little more info on pros and cons of factory\service approaches.

  • Haresh 9 January, 2015, 18:11

    After seeing your tutorial I can started with AngularJS Project. THANKS………..

  • evans 14 January, 2015, 21:32

    it was very helpful. thanks

  • Tuan Nguyen 16 January, 2015, 16:01

    Thanks so much! I can see how service and factory work and how they connect with controller

  • Nishant 20 January, 2015, 18:20

    Thanks for the tutorial..
    the simplified way in which you explained the concepts is commendable

  • Venkata SubbaReddy 27 January, 2015, 14:43

    Very good Example and Easy to Under stand for Every one. Thanks Lot

  • anil 28 January, 2015, 11:50

    is there any way to create multiple instances of a factory in another factory ?
    //factory 1
    module.factory(‘MyService’, function() {

    });

    //factory2
    module.factory(‘MyService1′, [ ‘MyService’ , function( MyService) {
    var obj = new MyService();
    }]);

  • anil 28 January, 2015, 11:52

    is there any way to create multiple instances of a factory in another factory ?
    //factory 1
    module.factory(‘MyService’, function() {
    });
    //factory2
    module.factory(‘MyService1′, [ ‘MyService’ , function( MyService) {
    var obj = new MyService();
    }]);

  • William 30 January, 2015, 14:09

    This was an incredibly well-written and informative tutorial. Thanks for sharing your wealth of knowledge. This really clarified things for me. Cheers again!

  • Sumanth 3 February, 2015, 9:00

    Thank you so much. This article helped me a lot in understanding AngularJS. This is very easy to follow.

  • Palak 4 February, 2015, 18:26

    Awesome article !!

  • Balachandar 4 February, 2015, 22:58

    Welldone…Excellent Explanation…Keep the good work…

  • channu yatnur 6 February, 2015, 16:30

    Thank you very much….great tutorial

  • Arun 6 February, 2015, 17:48

    nice article

  • Derek 9 February, 2015, 3:14

    Excellent tutorial. This is very clear and the example using the service approach works nicely! Thanks for posting it. You should help on the next O’Reilly Angular book. They could use it :-)

  • jdawg 10 February, 2015, 5:22

    Section one, last sentence, “Thus our application becomes for modular and testable.” I think you meant to write more, not for.

    Thanks,

    Grammar Guy

  • jdawg 10 February, 2015, 5:26

    Section one, third paragraph, first sentence. “Thus service is a stateless object that contains some useful functions.” I think you meant to write The, not Thus…

  • Abu Noman 12 February, 2015, 17:04

    Nice tutorial, Good job…… Thnx

  • Catatan Belajar 13 February, 2015, 14:24

    Thank you. It’s easy to follow.

  • rohini 24 February, 2015, 10:56

    Very good tutorial really even for beginners also it’s very easy to understand not only this post for Java, JQuery,spring i am getting good knowledge from this site….Thank you so much viral

  • Himali 24 February, 2015, 11:40

    Its great tutorial for beginner!!! Thank you a lot!!!

  • Adonis 24 February, 2015, 13:25

    Thanks a lot, this was very informative about controllers and services. Well done.

  • Chandra Shelar 24 February, 2015, 21:48

    Very simple way to explain. I cleared my concepts using your articles & examples.
    Can you please add custom directive tutorial?

    Thnx
    Chandra

  • Stephen Garside 6 March, 2015, 16:27

    Great article, much easier to follow than a lot on the web – at last an article that KISS!

  • A 14 March, 2015, 11:28

    This was lucid. Thanks for taking time to write this.

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