JSFiddle - React, Tailwind, and code Playground

HTML

<p>Name: <input id="john" type="text" value="" name="user"></p>
<input type="hidden" value="John" />
<span>Set value</span>

JavaScript

$("span").click(function(){
   var s= $('input[type="hidden"]').val();
   $("#john").val(s);
});