JSFiddle - React, Tailwind, and code Playground

HTML

<select id="selectbox">
    <optgroup label="optGroup1">
        <option>aaaa</option>
        
    </optgroup>
    
</select>

JavaScript

$(document).ready(function() {
var select = document.getElementById("selectbox");
option = document.createElement( 'option' );
option.value = option.text = "test";
select.add( option );
});