JSFiddle - React, Tailwind, and code Playground
HTML
<div id="selects">
<select name="folder1"></select>
<select name="folder2"></select>
<select name="folder3"></select>
</div>
JavaScript
var itemName = "folder4";
var $item = $('#selects select[name="' + itemName + '"]');
if($item.length == 0)
{
$('#selects').append('<select name="' + itemName + '"></select>');
}