ember js中的级联选择数据绑定

import Ember from 'ember';

export default Ember.Controller.extend({
  selectedCountry: null,
  selectedCity: null,

  countries: ['China', 'USA', 'Japan'],
  
  cities: Ember.computed('selectedCountry', function() {
    let selectedCountry = this.get('selectedCountry');
    
    if (selectedCountry === 'China') {
      return ['Beijing', 'Shanghai', 'Guangzhou'];
    } else if (selectedCountry === 'USA') {
      return ['New York', 'Los Angeles', 'Chicago'];
    } else if (selectedCountry === 'Japan') {
      return ['Tokyo', 'Osaka', 'Kyoto'];
    } else {
      return [];
    }
  })
});

<label>Country:</label>
{{#select value=selectedCountry}}
  {{#each countries as |country|}}
    <option value={{country}}>{{country}}</option>
  {{/each}}
{{/select}}

<label>City:</label>
{{#select value=selectedCity}}
  {{#each cities as |city|}}
    <option value={{city}}>{{city}}</option>
  {{/each}}
{{/select}}