<asp:FileUpload ID="fuMain" runat="server" />
<asp:Button ID="btnUpload" runat="server" OnClientClick="return CheckWorkFile()" Text="上傳" />

<input type="file" ID="fuMain" />
<input type="button" ID="btnUpload" onclick="return CheckWorkFile()" Text="上傳" />

function CheckWorkFile()
{
var obj=document.getElementById('fuMain');
if(obj.value=='')
{
alert('請選擇要上傳的作業書文件');
return false;
}
var stuff=obj.value.match(/^(.*)(/.)(.{1,8})$/)[3];
if(stuff!='doc')
{
alert('文件類型不正確，請選擇.doc文件');
return false;
}
return true;
}