Nav Guard 1

nav1.ts

export class MyClass { 
  constructor (public navCtrl: NavController) {}
  //When trying to leave the page will call 
  //ionViewCanLeave()
  pushPage() {
    this.navCtrl.push(DetailPage)
         .catch(()=> console.log(‘Something cache!’))
  }
  isValid() {
    return (validValue) ? true : false;
  }
  //Make a decision to stay or leave.
  ionViewCanLeave(): boolean { 
    return this.isValid();
  }
}