如何检查两个不同的子下拉列表在Angular 7中是否具有相同的值？

<select [(ngModel)]="firstDropdownValue">
  <option *ngFor="let option of firstDropdownOptions" [value]="option">{{ option }}</option>
</select>

<select [(ngModel)]="secondDropdownValue">
  <option *ngFor="let option of secondDropdownOptions" [value]="option">{{ option }}</option>
</select>

firstDropdownValue: string;
secondDropdownValue: string;

checkDropdownValues(): boolean {
  return this.firstDropdownValue === this.secondDropdownValue;
}

<button (click)="checkDropdownValues()">检查值</button>