无法从angular 6中的Firebase获取用户列表

// 在服务中，例如名为FirebaseService的服务
import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';

@Injectable()
export class FirebaseService {
  constructor(private http: HttpClient) {}

  getUsers(): Promise<any> {
    return this.http.get('https://your-firebase-project.firebaseio.com/users.json')
      .toPromise()
      .then(response => response)
      .catch(error => console.log(error));
  }
}

// 在组件中，例如名为UserListComponent的组件
import { Component, OnInit } from '@angular/core';
import { FirebaseService } from 'path-to-firebase-service';

@Component({
  selector: 'app-user-list',
  template: `
    <h2>User List</h2>
    <ul>
      <li *ngFor="let user of users">{{ user.name }}</li>
    </ul>
  `
})
export class UserListComponent implements OnInit {
  users: any[];

  constructor(private firebaseService: FirebaseService) {}

  ngOnInit() {
    this.firebaseService.getUsers()
      .then(users => this.users = users)
      .catch(error => console.log(error));
  }
}