title: why I got this.http.get(...).subscribe is not a function in angular2
body: <p>My code is </p>
  
  <pre>
      import 'rxjs/Rx';
      ...
      let _this = this;
      return new Promise(function(resolve, reject) {
          _this.http[method](url, data, {
              headers: headers
          })
          .toPromise()
          .then(
              (data) => {
                  resolve(data);
              },
              error => {
                  reject(error);
              }
          );
      });
  
  </pre>
  
  <p>The "subscribe" not come from my code, looks like it's angular original something.</p>
  
  <p>Error message:</p>
  
  <pre>
  EXCEPTION: Error: Uncaught (in promise): TypeError: _this.http.get(...).subscribe is not a function
  </pre>