Page not updated after var changed

I have a simple html page with simple var. I implemented counter info, simple countdown in seconds.

<div>TEST '{{ counter }}'</div>
counter = 10;

ionViewWillEnter() {
      this.checkTimer();
}   
checkTimer() {
    var me = this;
    setTimeout(function() { 
        me.counter -= 1;
        me.checkTimer();
        alert(me.counter);
    }, 1000);
  }

I don’t understand why it works on android but not on apple. The metod is called but on the gui value not updated. How Can force refresh page?