Injectable装饰器特定于Angular2的TypeScript风格。它使类构造函数可以通过TypeScript类型注释为DI隐式注释。在TS中是多余的，在JS中对于用注释的注入依赖项则不需要Inject。

Angular 2注入对象（类和构造函数）应该在引擎盖下带有annotations，parameters静态属性进行注释。

annotations是一个数组，其中包含new用于可注入类的ed装饰器：

function SomeComponent(...) {}
SomeComponent.annotations = [new Componenent(...)];

parameters是一个包含用于构造函数参数的修饰符的数组，每个元素是一个包含new用于相应构造函数属性的ed装饰符列表的数组（类似于$injectAngular1.x中的属性显式注释）：

function Service(someService, anotherService) {}
Service.parameters = [
  [new Inject(SomeService)],
  [new Inject(AnotherService), new Optional, new SkipSelf]
];

所有类装饰器都从扩展TypeDecorator，意味着它们可以被称为函数。在这种情况下，使用所谓的DSL语法，该语法允许将装饰器与Class辅助函数链接在一起：

var SomeComponent = Componenent(...).Class(...);

Class也可以单独使用，它从给定的定义对象构造一个新类，并允许constructor使用数组对方法进行注释（类似于Angular 1.x中的内联数组显式注释）：

var SomeService = Class({
  constructor: [[new Inject(SomeService)], function (someService) {}]
});

Class在最新的框架版本中不推荐使用helper。应该在ES5中将其替换为原始函数或第三方类帮助器。装饰器支持与类函数直接链接Componenent(...)(ComponentClass)。

Angular 2/4 ES6与 System.import

Promise.all([
  System.import('@angular/core'),
  System.import('@angular/platform-browser'),
  System.import('@angular/platform-browser-dynamic')
])
.then(([
  {Component, Inject, Injectable, Optional, NgModule, OpaqueToken},
  {BrowserModule},
  {platformBrowserDynamic}
]) => {

  const CONSTANT = { value: 'constant' };
  const CONSTANT_TOKEN = new OpaqueToken;
  const CONSTANT_PROVIDER = { provide: CONSTANT_TOKEN, useValue: CONSTANT };

  class Service {
    constructor(constant) {}
  }
  Service.parameters = [[new Inject(CONSTANT_TOKEN)]];

  class AppComponent {
    constructor(service, constant) {}
  }
  AppComponent.annotations = [new Component({
    selector: 'app',
    template: '...',
    providers: [Service, CONSTANT_PROVIDER]
  })];
  AppComponent.parameters = [[new Inject(Service)], [new Inject(CONSTANT_TOKEN)]];

  class AppModule {}
  AppModule.annotations = [new NgModule({
    imports: [BrowserModule],
    declarations: [AppComponent],
    bootstrap: [AppComponent]
  })];

  platformBrowserDynamic().bootstrapModule(AppModule);

})
.catch((err) => console.error(err));

带有UMD模块和ng全局模块的Angular 2/4 ES5

var Class = ng.core.Class;
var Component = ng.core.Component;
var Inject = ng.core.Inject;
var Injectable = ng.core.Injectable;
var NgModule = ng.core.NgModule;
var OpaqueToken = ng.core.OpaqueToken;

var BrowserModule = ng.platformBrowser.BrowserModule;
var platformBrowserDynamic = ng.platformBrowserDynamic.platformBrowserDynamic;

var CONSTANT = { value: 'constant' };
var CONSTANT_TOKEN = new OpaqueToken;
var CONSTANT_PROVIDER = { provide: CONSTANT_TOKEN, useValue: CONSTANT };

// Class helper function that uses A1-flavoured inline array DI annotations
// and creates an annotated constructor
var Service = Class({
  constructor: [[new Inject(CONSTANT_TOKEN)], function (constant) {
    console.log('Service constructor', constant);
  }]
});
// can also be
// function Service(constant) {};
// Service.parameters = [[new Inject(...)], ...];

// when not being `new`ed, Component is a chainable factory that has Class helper method
var AppComponent = Component({
  selector: 'app', 
  template: '...',
  providers: [Service, CONSTANT_PROVIDER]
})
.Class({
  constructor: [
    [new Inject(Service)],
    [new Inject(CONSTANT_TOKEN)],
    function (service, constant) {
      console.log('AppComponent constructor', service, constant);
    }
  ]
});
// can also be
// function AppComponent(...) {};
// AppComponent.annotations = [new Component(...)];
// AppComponent.parameters = [[new Inject(...)], ...];

var AppModule = NgModule({
  imports: [BrowserModule],
  declarations: [AppComponent],
  bootstrap: [AppComponent]
})
.Class({ constructor: function () {} });
// can also be
// function AppModule() {};
// AppModule.annotations = [new NgModule(...)];

platformBrowserDynamic().bootstrapModule(AppModule);