如何在 Angular 6 中创建级联下拉列表（国家和州列表）

如何在 Angular 6 中创建级联下拉列表（国家/地区和州列表）。我想要在 Angular 6 中创建一个完整的国家/地区和州列表。

任何知道这一点的人请分享你的想法。

演示---->级联下拉菜单（国家和州列表） https://stackblitz.com/edit/angular-qvqqgc

HTML:

<label>Country</label>
<div  title="Please select the country that the customer will primarily be served from">
    <select placeholder="Phantasyland" (change)="changeCountry($event.target.value)">
        <option *ngFor ="let count of countryList">{{count.name}} </option>
    </select>
</div>


<label>City</label>
<div title="Please select the city that the customer is primarily to be served from.">
    <select placeholder="Anycity">
        <option *ngFor ="let city of cities">{{city}} </option>
  </select>
</div>

TS:

countryList: Array<any> = [
    { name: 'Germany', cities: ['Duesseldorf', 'Leinfelden-Echterdingen', 'Eschborn'] },
    { name: 'Spain', cities: ['Barcelona'] },
    { name: 'USA', cities: ['Downers Grove'] },
    { name: 'Mexico', cities: ['Puebla'] },
    { name: 'China', cities: ['Beijing'] },
  ];
  cities: Array<any>;
  changeCountry(count) {
    this.cities = this.countryList.find(con => con.name == count).cities;
  }