<html>
<head>
<meta charset='utf-8'>
<meta name="viewport" content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
<script type="text/javascript" src="http://mat1.gtimg.com/libs/jquery2/2.2.0/jquery.js"></script>
<body>
<form action="upload.html" method="post" enctype="multipart/form-data" accept-charset="utf-8">
<input id="file" type="file" name="选择文件"><br/>
<input id="fileUpload" type="submit" value="提交">
</form>
<script type="text/javascript">
$("#fileUpload").click(function(){
if($("input[type='file']").val()==""){
alert("请选择文件后提交");
return false;
}else{
return true;
}
})
</script>
</body>
</html>
空文件就不要让提交