问Angular 4 api调用json搜索功能

EN

<input
    (keyup)="searchTerm$.next($event.target.value)">

<ul *ngIf="results">
  <li *ngFor="let result of results">
    <a href="{{ result.latest }}" target="_blank">
      {{ result.title }}
    </a>
  </li>
</ul>

import { Injectable } from '@angular/core';
import { Http, Response } from '@angular/http';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/debounceTime';
import 'rxjs/add/operator/distinctUntilChanged';
import 'rxjs/add/operator/switchMap';

@Injectable()

export class AppService {
  baseUrl: string = 'https://raw.githubusercontent.com/elena-in-code/books/master/bookcollection.json';
queryUrl: string = '?search=';


  constructor(private http:Http){}

  search(terms: Observable<string>) {
    return terms.debounceTime(400)
      .distinctUntilChanged()
      .switchMap(term => this.searchEntries(term));
  }

  searchEntries(term) {
    return this.http
        .get(this.baseUrl + this.queryUrl + term)
        .map(res => res.json());
  }
}

import { Component, OnInit } from '@angular/core';
import { AppService } from './app.service';
import {Observable} from 'rxjs/Observable';
import { Subject } from 'rxjs/Subject';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/debounceTime';
import 'rxjs/add/operator/distinctUntilChanged';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css'],
  providers: [AppService]
})
export class AppComponent  {
  results: Object;
  searchTerm$ = new Subject<string>();

  constructor(private appService: AppService){
    this.appService.search(this.searchTerm$)
      .subscribe(results => {
        this.results = results.results;
      });
  }
}

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { HttpModule } from '@angular/http';
import { FormsModule, ReactiveFormsModule } from '@angular/forms';
import {NgbModule} from '@ng-bootstrap/ng-bootstrap';

import { AppComponent } from './app.component';
import { AppService } from './app.service';

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule, 
    HttpModule, 
    FormsModule
  ],
  providers: [AppService],
  bootstrap: [AppComponent]
})
export class AppModule { }