get value ion- select since TS, using ionic v3

Question

I have two ion select and I would like to capture the value of each select from the TS when I click a button. Please help

part of code:

<ion-item>
  <ion-label class="lbReward" color="dark" >Reward Type:  </ion-label>
  <ion-select (ionChange) = "onChange()"   [ngModel] = "selectedRewardType">
    <ion-option value="priceDiscount">Total Price Discount</ion-option>
    <ion-option value="categoryDiscount">Category Price Discount</ion-option> 
    <ion-option value="freeGiftwithPrice">Sufficient Price Free Gift</ion-option>
    <ion-option value="freeGiftwithMeal">Meal with Free Gift</ion-option>
  </ion-select>
</ion-item>