获取上传文件类型!

<input type="file" onchange="checkExt(this)"/>

<script type="text/javascript">
var checkExt=function(file) {
if(!(/(?:jpg|gif)$/i.test(file.value))) {
alert("只允许上传jpg和gif的图片");
if(window.ActiveXObject) {//for IE
file.select();//选择后清空文件框
document.selection.clear();
} else if(window.opera) {//for opera
file.type="text";file.type="file";
} else file.value="";//for FF,Chrome,Safari
} else {
alert("ok");
}
};
</script>