JSFiddle - React, Tailwind, and code Playground

HTML

<form name=form>
<input name=a onchange="c.value = add(value,b.value)"> +
<input name=b onchange="c.value = add(a.value,value)"> =
<input name=c readonly value="Hello World!">
</form>
<form name=form2>
    <input name=d value="Hello World!" onclick=alert(form)>
</form>

JavaScript

//if(!form) { var form = document.forms.form; }
function add(x,y) {
    return parseInt(x) + parseInt(y);
}