JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://ajax.aspnetcdn.com/ajax/jquery.validate/1.9/jquery.validate.js"></script>
<div>
  <form method='post' name='login'>
    <input type='text' name='user[]' class='add-new'/>
  </form>
</div>

JavaScript

$('form').on('click', '.add-new', function() {
    $(this).removeClass('add-new');
    $(this).closest('form').append("<br><input type='text' name='user[]' class='add-new'/>");
});