Fill Textbox automatically from typing into another textbox

Hi, I am working in Angular.

I have two text box 1. is Email and 2. is Username

I want to fill textbox username from email. because it has same value. textbox username is disabled. so how can I fill same value from email.

Email : <input type="text" required email #email="ngModel" name="email" class="form-control" [(ngModel)]="userModel.email" placeholder="Email"/>
User Name : <input type="text" required #userName="ngModel" name="userName" class="form-control" [(ngModel)]="userModel.userName" placeholder="User Name" disabled/>