JSFiddle - React, Tailwind, and code Playground

HTML

<form action="#" method="post" id="demoForm" class="demoForm">
	<select name="demoSel[]" id="demoSel" size="10" multiple>
		<option value="scroll">Scrolling Divs JavaScript</option>
		<option value="tooltip">JavaScript Tooltips</option>
		<option value="con_scroll">Continuous Scroller</option>
		<option value="banner">Rotating Banner JavaScript</option>
		<option value="random_img">Random Image PHP</option>
		<option value="form_builder">PHP Form Generator</option>
		<option value="table_class">PHP Table Class</option>
		<option value="order_forms">PHP Order Forms</option>
	</select>
</form>

JavaScript

document.getElementById('demoSel').onchange = function(e) {
	alert(document.getElementById('demoSel').value);
}