JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" name="first" value="" /><br />
<input type="text" name="second" value="" /><br />

This is "hidden" but shown here so you can see whats happening: <br />
<input type="text" name="name" value="" /><br />

JavaScript

var $hidden = $('[name=name]'), 
    $first = $('[name=first]'), 
    $second = $('[name=second]');
$first.add($second).bind('keyup change', function(e) {
    $hidden.val($.trim($first.val()+' '+$second.val()));
});