Angular 2:在ngModelChange函数中，如何比较ngModel的新旧值？

import { Component } from '@angular/core';

@Component({
  selector: 'app-example',
  template: `
    <input [(ngModel)]="value" (ngModelChange)="onValueChange($event)">
  `
})
export class ExampleComponent {
  value: string;
  oldValue: string;

  onValueChange(newValue: string) {
    // 比较ngModel的新旧值
    if (newValue !== this.oldValue) {
      console.log('ngModel的值发生了变化');
    }

    // 更新旧值为新值
    this.oldValue = newValue;
  }
}