JSFiddle - React, Tailwind, and code Playground

by VixedS

HTML

<input id="id_email" placeholder="Email here" />
<input id="id_username" placeholder="Username here" disabled />

CSS

input{
  display:block;
  margin:20px auto;
  padding:10px 20px;
}

JavaScript

$('#id_email').on('input',function(){
        $('#id_username').val($(this).val().split('@')[0]);
});