JSFiddle - React, Tailwind, and code Playground

HTML

<select id="select" name="ps" onchange="selectionchanged(this);">
<option value="1" subvalue="red">one</option>
<option value="2" subvalue="green">two</option>
<option value="3" subvalue="yellow">three</option>
</select>
<div>subvalue: </div>
<div id="results">red</div>

JavaScript

var resultEl = document.getElementById("results");

window.selectionchanged = function(select) {
    var index = select.selectedIndex;
    var selectedOption = select.options[index];
    var subvalue = selectedOption.getAttribute('subvalue');

    document.getElementById("results").textContent = subvalue;
}
document.addEventListener('DOMContentLoaded',function(){
window.selectionchanged(document.getElementById("select"));
})