AngularJS : What is a factory?

I've been doing a lot of work on Angular.js and overall I find it to be an interesting and powerful framework.

I know there have been a lot of discussions on Services vs. Factories vs. Providers vs. Values, but I am still pretty confused about what a Factory is.

Factory has been defined in other StackOverflow discussions as the following:

Factories

Syntax: module.factory( 'factoryName', function ); Result: 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.

I find this explanation to be very difficult to grasp and it doesn't increase my understanding of what a factory is.

Would anyone have any explanations or real life examples to share about what exactly a Factory is and why you should use it in lieu of a Service, Provider, or other?

Update

A service holds a reference to any object.

A factory is a function which returns any object

A provider is a function which returns any function

-phew-

From what I understand they are all pretty much the same. The major differences are their complexities. Providers are configurable at runtime, factories are a little more robust, and services are the simplest form.

Check out this question https://stackoverflow.com/questions/15666048/angular-js-service-vs-provide-vs-factory

Also this gist may be helpful in understanding the subtle differences.

Source: https://groups.google.com/forum/#!topic/angular/hVrkvaHGOfc

jsFiddle: http://jsfiddle.net/pkozlowski_opensource/PxdSP/14/

author: Pawel Kozlowski

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

//service style, probably the simplest one
myApp.service('helloWorldFromService', function() {
    this.sayHello = function() {
        return "Hello, World!";
    };
});

//factory style, more involved but more sophisticated
myApp.factory('helloWorldFromFactory', function() {
    return {
        sayHello: function() {
            return "Hello, World!";
        }
    };
});

//provider style, full blown, configurable version     
myApp.provider('helloWorld', function() {
    // In the provider function, you cannot inject any
    // service or factory. This can only be done at the
    // "$get" method.

    this.name = 'Default';

    this.$get = function() {
        var name = this.name;
        return {
            sayHello: function() {
                return "Hello, " + name + "!";
            }
        };
    };

    this.setName = function(name) {
        this.name = name;
    };
});

//hey, we can configure a provider!            
myApp.config(function(helloWorldProvider){
    helloWorldProvider.setName('World');
});
    

function MyCtrl($scope, helloWorld, helloWorldFromFactory, helloWorldFromService) {

    $scope.hellos = [
        helloWorld.sayHello(),
        helloWorldFromFactory.sayHello(),
        helloWorldFromService.sayHello()];
}​

One major difference I see is that you can run custom code in the factory. But, in a service, only object creation happens.

myJs.factory('Factory', function() {

    //Write custom code here
   
    return {
            Hello: function() {
            return "Hello, World!"
        }
    };
});

My two cents on this topic. I am a very very newbie and just into understanding Angular JS and this was one of the things that confused me a lot and hence I studied it in somewhat detail. I have been making notes for giving interviews and this may be useful to others.

• service and factory do the same things in different ways
• both are injectibles
• for most things use factory syntax
• easier to understand
• nowadays with es6 "service" is done since it converts to es6 classes better
• its essentially abstracting away business logic from the controller
• if you use biz logic with controllers then you can only use with controllers
• controller is for putting data on scope not processing lengthy biz logic
• so what happens in above scenario is that complex biz logic is tied up into controllers. Not for processing data. So put bits and pieces of it into services or factory. So your code is lean and modular.
• services are singletons

Services are mostly objects in which you describe the constructor class of the object. Somewhere deep within the framework, the Object.create() function is called and then you can use a service by calling its object and methods using a controller. Factory, on the other hand, doesn't create an object by default and hence requires you to return the entire object location once you're done defining all the attributes and methods.