ionic-framework/angular/test/test-app/src/app/alert/alert.component.ts

import { Component, NgZone } from '@angular/core';
import { AlertController } from '@ionic/angular';
import { NavComponent } from '../nav/nav.component';

@Component({
  selector: 'app-alert',
  templateUrl: './alert.component.html',
})
export class AlertComponent {

  constructor(
    private alertCtrl: AlertController
  ) { }

  async openAlert() {
    const alert = await this.alertCtrl.create({
      header: 'Hello',
      message: 'Some text',
      buttons: [
        {
          role: 'cancel',
          text: 'Cancel',
          handler: () => {
            NgZone.assertInAngularZone();
          }
        }
      ]
    });
    await alert.present();
  }
}