JSFiddle - React, Tailwind, and code Playground

HTML

<h1>How to measure size of an expanded combo box?</h1>	

<select>
		<option>111111111111111</option>
		<option>2222222222222</option>
		<option>33333333333</option>
</select>

<div id="log"></div>

JavaScript

$("select").on("change", function() {
	$("#log").html($("select").width() + " " + $(this).height());
});