what is the use of ng model change code example

Example 1: ngmodel change

<select [ngModel]="selectedItem" (ngModelChange)="onChange($event)">
onChange(newValue) {
    console.log(newValue);
    this.selectedItem = newValue;  // don't forget to update the model here
    // ... do other stuff here ...
}

Example 2: ng model on change

<select [ngModel]="selectedItem" (ngModelChange)="onChange($event)">