JSFiddle - React, Tailwind, and code Playground

HTML

<form>
 <input name=a type=number value='' oninput='checka();'>
 <input name=b type=number value='' oninput='checkb(this);'>
</form>
    
<script>
 function checka() {
  alert(isNaN(document.forms[0].a.value));
 }

 function checkb(A) {
  alert(isNaN(this.value));
 }
</script>