<form name=form><input name=jts value="" size=10><input type="file" name=upf onchange="ty()";></form><script> function ty(){var srcc = document.form.upf.value;srcc = srcc.toString()start = srcc.indexOf(".");end = srcc.length;ts=srcc.substring(start+1,end);//sWordmaple javascript article.nts=ts.toLowerCase();document.form.jts.value=nts;alert("你选择的文件类型是"+document.form.jts.value+"!");}</script>
(出处:http://www.sheup.com)