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    <p>From the AngularJS mailing list I got <a href="https://groups.google.com/forum/#!msg/angular/56sdORWEoqg/HuZsOsMvKv4J">an amazing thread</a> that explains service vs factory vs provider and their injection usage. Compiling the answers:</p> <h1>Services</h1> <p>Syntax: <code>module.service( 'serviceName', function );</code> <br/> Result: When declaring serviceName as an injectable argument <strong>you will be provided with an instance of the function. In other words</strong> <code>new FunctionYouPassedToService()</code>.</p> <h1>Factories</h1> <p>Syntax: <code>module.factory( 'factoryName', function );</code> <br/> Result: When declaring factoryName as an injectable argument you will be provided with <strong>the value that is returned by invoking the function reference passed to module.factory</strong>.</p> <h1>Providers</h1> <p>Syntax: <code>module.provider( 'providerName', function );</code> <br/> Result: When declaring providerName as an injectable argument <strong>you will be provided with</strong> <code>(new ProviderFunction()).$get()</code>. The constructor function is instantiated before the $get method is called - <code>ProviderFunction</code> is the function reference passed to module.provider.</p> <p>Providers have the advantage that they can be configured during the module configuration phase.</p> <p>See <a href="http://jsbin.com/ohamub/1/edit">here</a> for the provided code.</p> <p>Here's a great further explanation by Misko:</p> <pre><code>provide.value('a', 123); function Controller(a) { expect(a).toEqual(123); } </code></pre> <p>In this case the injector simply returns the value as is. But what if you want to compute the value? Then use a factory</p> <pre><code>provide.factory('b', function(a) { return a*2; }); function Controller(b) { expect(b).toEqual(246); } </code></pre> <p>So <code>factory</code> is a function which is responsible for creating the value. Notice that the factory function can ask for other dependencies.</p> <p>But what if you want to be more OO and have a class called Greeter?</p> <pre><code>function Greeter(a) { this.greet = function() { return 'Hello ' + a; } } </code></pre> <p>Then to instantiate you would have to write</p> <pre><code>provide.factory('greeter', function(a) { return new Greeter(a); }); </code></pre> <p>Then we could ask for 'greeter' in controller like this</p> <pre><code>function Controller(greeter) { expect(greeter instanceof Greeter).toBe(true); expect(greeter.greet()).toEqual('Hello 123'); } </code></pre> <p>But that is way too wordy. A shorter way to write this would be <code>provider.service('greeter', Greeter);</code></p> <p>But what if we wanted to configure the <code>Greeter</code> class before the injection? Then we could write</p> <pre><code>provide.provider('greeter2', function() { var salutation = 'Hello'; this.setSalutation = function(s) { salutation = s; } function Greeter(a) { this.greet = function() { return salutation + ' ' + a; } } this.$get = function(a) { return new Greeter(a); }; }); </code></pre> <p>Then we can do this: </p> <pre><code>angular.module('abc', []).config(function(greeter2Provider) { greeter2Provider.setSalutation('Halo'); }); function Controller(greeter2) { expect(greeter2.greet()).toEqual('Halo 123'); } </code></pre> <p>As a side note, <code>service</code>, <code>factory</code>, and <code>value</code> are all derived from provider.</p> <pre><code>provider.service = function(name, Class) { provider.provide(name, function() { this.$get = function($injector) { return $injector.instantiate(Class); }; }); } provider.factory = function(name, factory) { provider.provide(name, function() { this.$get = function($injector) { return $injector.invoke(factory); }; }); } provider.value = function(name, value) { provider.factory(name, function() { return value; }); }; </code></pre>
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    1. POAngularJS: Service vs provider vs factory
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    1. COSee also http://stackoverflow.com/a/13763886/215945 which discusses the differences between service and factory.
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    2. COIn edit 611 I added usage of angular constants and values. To demonstrate the differences of the the other's already shown. http://jsbin.com/ohamub/611/edit
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    3. COAlthough a service is called by creating an instance of the function. It is actually created only once per injector which makes it like singleton.http://docs.angularjs.org/guide/dev_guide.services.creating_services
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