<html>
<body>
<select id="select1" style="width:100px;" onchange="checkStringWidth()">
<option value="1">abcde abcde abcde abcde abcde</option>
<option value="2">abcde abcde abcde abcde</option>
</select>
<br>
Selected option: <span id="span1"></span>
<br>
Text width: <span id="lbWidth"></span>
</body>
</html>
<script>
function checkStringWidth() {
var select1 = document.getElementById('select1');
var span1 = document.getElementById('span1');
var lbWidth = document.getElementById('lbWidth');
span1.innerHTML = select1.options[select1.selectedIndex].text;
lbWidth.innerHTML = span1.offsetWidth;
}
</script>