如果我没理解错的话，这应该就是你要找的东西，在html中添加一个事件到你的选择器中，如下所示（$event将检索选定的值）：

<select ng-model="visitors_list" id="visitors" (change)="onSelect($event)"> 
        <option class="dropdown-item" value="1">1</option>
        <option class="dropdown-item" value="2">2</option>
        <option class="dropdown-item" value="3">3</option>
        <option class="dropdown-item" value="4">4</option>
        <option class="dropdown-item" value="5">5</option>
</select>

在你的打字稿里：

export class YourComponent {

  selectedNumber!: number; // Create a variable called selectedNumber and set it to null.

  constructor() {}

  ngOnInit() {}

/**
 * The function takes an event as an argument, and sets the selectedNumber property to the value of the
 * event's target.
 * @param {any} event - any - The event object
 */
  onSelect(event: any) {
    this.selectedNumber = event.target.value;
  }

}

现在您可以随意使用变量了，希望我对您有所帮助