import {Injectable} from '@angular/core';
import {Http,Response} from "@angular/http";
import 'rxjs/Rx';

@Injectable()
export class HttpService{
    constructor(private http : Http){}

    getData(){
      return  this.http.get("URI")
      .map( (res: Response) => res.json()  );
    }
}

问题是,在运行时它抱怨：

res.json is not a function

我已将res的数据类型定义为Response,但仍然抱怨

.map( (res: Response) => res.json()  )

如果我用订阅替换地图它工作正常：

.subscribe( res =>{
                res.json();
                console.log("City is:"+ res.json().city.name)
            });