How to Inject Angular2 Http service into es6/7 Cla

问题:

If I use es6/7 (babel - stage 1) instead of TypeScript, how are services, and specifically Http, injected?

Here's my component JS:

import {Component, Inject, View, CORE_DIRECTIVES, ViewEncapsulation} from 'angular2/angular2';
import {Http} from 'angular2/http';

@Component({
  selector: 'login'
})
@View({
  templateUrl: './components/login/login.html',
  styleUrls: ['components/login/login.css'],
  directives: [CORE_DIRECTIVES],
  encapsulation: ViewEncapsulation.Emulated
})
export class Login {
  constructor(@Inject(Http) http) {
    console.log('http', http);
  }

  authenticate(username, password) {
    // this.http.get('/login');
  }
}

I have tried:

export class Login {
  constructor(@Inject(Http) http) {
    console.log('http', http);
  }
}
/********************/
@Inject(Http)
export class Login {
  constructor(http) {
    console.log('http', http);
  }
}
/********************/
export class Login {
  constructor(Http: http) {
    console.log('http', http);
  }
}
/********************/
export class Login {
  constructor(http = Http) {
    console.log('http', http);
  }
}
/********************/
export class Login {
  constructor(Http) {
    this.http = new Http()
    console.log('http', this.http);
  }
}
/********************/
export class Login {
  constructor(http = new Http()) {
    console.log('http', http);
  }
}

All but the first compiles. Others give me access to either the Http class or an http instance. But none works.

I tried to following the discussion referenced by Eric Martinez in his comment. Login.js now:

import {Component, Inject, View, CORE_DIRECTIVES, ViewEncapsulation} from 'angular2/angular2';
import {HTTP_BINDINGS, Http, BaseRequestOptions, RequestOptions, RequestMethods} from 'angular2/http';

@Component({
  selector: 'login'
})
@View({
  templateUrl: './components/login/login.html',
  styleUrls: ['components/login/login.css'],
  directives: [CORE_DIRECTIVES],
  encapsulation: ViewEncapsulation.Emulated,
  bindings: [Http]
})
export class Login {

  constructor(http) {
    this.http = http;
    console.log('http', http);
  }

  authenticate(usernameEl, passwordEl) {
    var username = usernameEl.value;
    var password = passwordEl.value;
    console.log('username', username, password);

    // this.http.get('/login');
  }
}

Login.parameters = [Http];

It compiles now but generates the following error:

Uncaught (in promise) NoBindingError {message: "No provider for Http! (Login -> Http)", stack: "Error: DI Exception↵ at NoBindingError.BaseExce…or._new (http://localhost:3000/bundle.js:7319:22)", keys: Array[2], injectors: Array[2]}constructResolvingMessage: (keys)arguments: (...)caller: (...)length: 1name: ""prototype: Object__proto__: ()context: (...)injectors: Array[2]0: Injector1: Injectorlength: 2__proto__: Array[0]keys: Array[2]message: "No provider for Http! (Login -> Http)"stack: "Error: DI Exception↵ at NoBindingError.BaseException [as constructor] (http://localhost:3000/bundle.js:8400:24)↵ at NoBindingError.AbstractBindingError [as constructor] (http://localhost:3000/bundle.js:9066:17)↵ at new NoBindingError (http://localhost:3000/bundle.js:9102:17)↵ at Injector._throwOrNull (http://localhost:3000/bundle.js:7469:20)↵ at Injector._getByKeyDefault (http://localhost:3000/bundle.js:7516:22)↵
at Injector._getByKey (http://localhost:3000/bundle.js:7461:26)↵ at Injector._getByDependency (http://localhost:3000/bundle.js:7447:26)↵
at Injector._instantiate (http://localhost:3000/bundle.js:7339:37)↵
at Injector._instantiateBinding (http://localhost:3000/bundle.js:7330:26)↵ at Injector._new (http://localhost:3000/bundle.js:7319:22)"proto: __

回答1:

Since you have @Decorators enabled in Babel

...I'll fine-tune this answer to work with your specific setup.

1. You're missing HTTP_PROVIDERS

The HTTP_PROVIDERS constant includes a number of functions required to handle HTTP requests/responses.

import {Http, HTTP_PROVIDERS} from 'angular2/http';    

@Component({
  selector: 'login',
  providers: [ HTTP_PROVIDERS ]
})

2. You need to desugar the DI (Dependency Injection) syntax

As mentioned in @alexpods' answer.

Remove the static typing

constructor(http) {

@Inject handles DI implicitly but is only supported in Angular2+Typescript. Since you're using Angular2+ES6 you need to attach a static getter parameter to your class to provide the ES6-specific equivalent.

static get parameters() {
    return [[Http]];
}

3. You need to bind the Http instance to your class in the constructor

By doing this, it will become accessible in your authenticate() method.

constructor(http) {
    this.http = http;
    console.log('http', this.http);
}

---

...and the full implementation:

import {Component, Inject, View, CORE_DIRECTIVES, ViewEncapsulation} from 'angular2/angular2';
import {Http, HTTP_PROVIDERS} from 'angular2/http';

@Component({
  selector: 'login',
  // required for Http
  providers: [ HTTP_PROVIDERS ]
})
@View({
  templateUrl: './components/login/login.html',
  styleUrls: ['components/login/login.css'],
  directives: [CORE_DIRECTIVES],
  encapsulation: ViewEncapsulation.Emulated
})
export class Login {
  constructor(http) {
    // bind http to your class during construction
    //   so it's available to authenticate()
    this.http = http;
  }

  // Angular2 DI desugar'd
  static get parameters() {
    return [[Http]];
  }

  authenticate(username, password) {
    this.http.get('/login');
  }
}

Aside: I know for a fact this works because I'm using it for the <ng2-markdown> component on EvanPlaice.com.

回答2:

How I've already answered it here, If you write code in ES7, use static getter for parameters property to specify injections into constructor of your component. For example:

import { Http } from 'angular2/http';
// other imports ...

// component decorators ...
export class Login {

  static get parameters() {
    return [[Http]];
  }

  constructor(http) {
    this.http = http;
    console.log('http', http);
  }

  // other methods
}

I think it most concise method at this moment.

Remember there is no proposal to support parameter decorators in ES7 at this moment (for example see this issue for Babel).

回答3:

Method from the official API Review works for me:

import {Http, HTTP_PROVIDERS} from 'angular2/http';
@Component({
  selector: 'http-app',
  viewProviders: [HTTP_PROVIDERS],
  templateUrl: 'people.html'
})
class PeopleComponent {
  constructor(http: Http) {
    http.get('people.json')
      .map(res => res.json())
      .subscribe(people => this.people = people);
  }
}

回答4:

With babel-plugin-angular2-annotations, you can inject services with constructor parameter type annotations just like TypeScript.

Install babel plugins:

npm install -D babel-plugin-angular2-annotations babel-plugin-transform-decorators-legacy babel-plugin-transform-class-properties babel-plugin-transform-flow-strip-types babel-preset-es2015

.babelrc:

{
  "plugins": [
    "angular2-annotations",
    "transform-decorators-legacy",
    "transform-class-properties",
    "transform-flow-strip-types"
  ],
  "presets": [
    "es2015"
  ]
}

and voila!

import {Component, View, CORE_DIRECTIVES, ViewEncapsulation} from 'angular2/angular2';
import {Http} from 'angular2/http';

@Component({
  selector: 'login'
})
@View({
  templateUrl: './components/login/login.html',
  styleUrls: ['components/login/login.css'],
  directives: [CORE_DIRECTIVES],
  encapsulation: ViewEncapsulation.Emulated
})
export class Login {
  constructor(http: Http) {
    console.log('http', http);
    this.http = http;
  }

  authenticate(username, password) {
    this.http.get('/login');
  }
}

Note that the type signature is used only for a hint for dependency injection and not used for type-checking.