选择中的 A​​ngular 2 更改选项

Question

我有 2 个选择：

 <form name="newDocumentForm">
<label for="companySelect"> Company: </label>
<select name="companySelect" id="companySelect" [(ngModel)]="companySelect" 
 (ngModelChange)="onChange($event)">
  <option [ngValue]="undefined" disabled selected>Select...</option>
  <option *ngFor="let company of companies" [ngValue]="company">{{company.name}}</option>
</select>

<label for="documentTypeSelect"> Type: </label>
<select name="documentTypeSelect" id="documentTypeSelect" 
 [(ngModel)]="documentTypeSelect">
  <option [ngValue]="undefined" disabled selected>Select...</option>
  <option value="aaa">ty</option>
  <option value="bbbb">ew</option>
</select>
</form>

每次我在第一次选择中更改某些内容时，我应该添加什么到 onChange($event) 以将 documentTypeSelect 选项设置为“选择...”？ 像this.documentTypeSelect = ???

Answer 1

改变

<option [ngValue]="undefined" 

到

<option [ngValue]="''"

如果您随后将companySelect 设置为''，则会选择此选项

companySelect:string = '';

更复杂的场景，另见Angular 2 Dropdown Options Default Value