<html>
<head>
<script type="text/javascript">
function checkUpload()
{
for(var i=0;i<document.files.filename.length;i++){
if(document.files.filename[i].value=="未选择文件"){
alert("请检查要上传的文件是否全部添加!");
return false;
}
}
}
</script>
</head>
<body>
<form name="files" enctype="multipart/form-data" method="POST" action="http://www.baidu.com" onsubmit="return checkUpload()">
<div class="file-btn-box">
<input type="button" class="add-btn" value="添加文件" onclick="addinput()">
<input type="submit" class="submit-btn" id="upload" value="上传" ><br>
</div>
<table id="file">
<input type="text" name="filename" >
<input type="text" name="filename" >
</table>
</form>
</body>
</html>
原文：http://blog.csdn.net/u013159040/article/details/46674387