AngularJS: Service、Factory、Provider

最近在接触 AngularJS， 被晦涩难懂的各种概念搞得头疼脑涨。Service、Factory、Provider 就是其中几个。

Factory

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

Result: the value that is returned by invoking the function reference passed to module.factory

source code: return factoryName = fn()

Note

1. Must return an object which is the main difference differentiates it with other design patterns. We can expose any functionality to where it be injected.

Services

Syntax: module.service('serviceName', function)

Result: we will be provided with an instance of the function. In other words new FunctionYouPassedToService()

source code: return serviceName = new fn()

Note:

1. Don’t need to return any object when create a AngularJS service for it can be instantiated by Angular self.

2. All we need to do is just add the functionality to this variable.

Provider

Syntax: module.provider('providerName', function)

Result: we will be provided with (new ProviderFunction()).$get()

source code: return providerName = (new fn()).$get()

Note

1. Provider is one of which can be configured (another is constant) during the module configuration phase

2. Expose any more functionality through provider add it under $get like:

   this.$get: function() {
     return {
       name: _name,
       getName: function() {
         return name
       }
     }
   }

Additional

When an AngularJS app is started, it has a certain “boot-order” (I think it same to life-cycle ?_?). From the perspective of a developer, it looks like this:

anuglar.module('myModule', [])
       .config(function(injectables) {  // providers & constants

       })
       .run(function(injectables) {
         // do initialization
       })

reference

AngularJS: Service vs Factory vs Providers made super simple – Ng-ninja

AngularJS: Service vs provider vs factory
– Stack Overflow

Additional

Constant

A constant can not be intercepted by a decorator, that means that the value of a constant should never be changed (though it is still possible to change it programmatically in Angular 1.x).

Value

A value is nothing more than a simple injectable value. The value can be a string, number but also a function. Value differs from constant in that value can not be injected into configurations, but it can be intercepted by decorators.

Decorator

A decorator can modify or encapsulate other providers. There is one exception and that a constant cannot be decorated.

##Summary

• All the providers are instantiated only once. That means that they are all singletons.
  All the providers except constant can be decorated.
• A constant is a value that can be injected everywhere. The value of a constant can never be changed.
• A value is just a simple injectable value.
• A service is an injectable constructor.
• A factory is an injectable function.
• A decorator can modify or encapsulate other providers except a constant.
• A provider is a configurable factory.