get the selected options and validate the number of marked options?

I’m using an ion-select and I’m enabling the multiple attribute to select several options. I can not find a way to disable the rest of the options in real time if 3 options have already been checked. I am currently using the ionSelect event, but it only works when an option is checked. How can I solve my problem? How can I solve my problem? I would like to understand how I know how many options I have marked and get their value in real time.

this is my code:


<ion-label>Select a person</ion-label>
<ion-select [(ngModel)]="person" multiple="true">
  <ion-option *ngFor="let item of options; let i = index" 
    [value]="" (ionSelect)="fn_checkOptions()" >

export class HomePage {
public options:object=[];

constructor(public navCtrl: NavController) {