可观察到的角度2警告

Question

我正在使用angular 2，我只是使用observable创建服务。 在控制台中，我看到一些警告。 这是我的服务

import { Injectable } from '@angular/core';
import {Http , Headers , Response , RequestOptions } from '@angular/http';
import {Phase} from '../classes/phase';
import { Observable } from 'rxjs/observable';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/catch';
import {PhaseParser} from '../parsers/phase-parser' ;
import * as globals from '../../globals';
import {User} from '../classes/user';

@Injectable()
export class LoginService {

  postData: string;
  puttData: string;
  private headers = new Headers({'Content-Type': 'application/json'});

  constructor( private _http: Http) { }
  /*
  // login  to the application
  login (body: User) {
    const json = JSON.stringify(body);
    const params = json;
    const headers = new Headers();
    headers.append('Content-type', 'application/json');
    return this._http.post(globals.serverIp + '/auth', params, {
      headers : headers
    })
      .map((res: Response) => res.json()).subscribe(data => this.postData = JSON.stringify(data),
        error => console.log(JSON.stringify(error)),
        () => console.log(JSON.stringify(this.postData)));
  }*/
  login(username: string, password: string): Observable<boolean> {
    return this._http.post( globals.serverIp + '/auth', JSON.stringify({username: username, password: password}), {headers: this.headers})
      .map((response: Response) => {
        // login successful if there's a jwt token in the response
        const token = response.json() && response.json().token;
        if (token) {
          // store username and jwt token in local storage to keep user logged in between page refreshes
          localStorage.setItem('currentUser', JSON.stringify({ username: username, token: token }));
          // return true to indicate successful login
          return true;
        } else {
          // return false to indicate failed login
          return false;
        }
      }).catch((error: any) => Observable.throw(error.json().error || 'Server error'));
  }

  getToken(): String {
    const currentUser = JSON.parse(localStorage.getItem('currentUser'));
    const token = currentUser && currentUser.token;
    return token ? token : '';
  }

  logout(): void {
    // clear token remove user from local storage to log user out
    localStorage.removeItem('currentUser');
  }



}

这是警告：

这个警告可以在我的项目中提供一些问题吗？ 提前谢谢你