Fileupload validation

function ValidateFileUpload(sender, args)
 {

document.getElementById('<%# cvFlpAttach.ClientID %>').innerHTML = "";

var fl = document.getElementById('<%# FlpAttach.ClientID %>').value;

if (fl != "") {

var ext = document.getElementById('<%# FlpAttach.ClientID %>').value;

if (ext.length > 0) {

var str = ext.substring(ext.lastIndexOf('\\') + 1);

var sInvalidChars = "#%@&*:<>?\/{|}~";

var myIndex = 0;

args.IsValid = false;

var index = 0;

while (index < str.length) {

if (sInvalidChars.indexOf(str.charAt(index)) != -1) {

myIndex = myIndex + 1;

}

index++;

}

ext = ext.substring(ext.lastIndexOf('.') + 1);

ext = ext.toLowerCase();

if (ext != "doc" && ext != "docx" && ext != "pdf" && ext != "xls" && ext != "xlsx" && ext != "msg" && ext != "txt" && ext != "jpeg" && ext != "png" && ext != "rtf" && ext != "gif" && ext != "pptx" && ext != "ppt" && ext != "pps" && ext != "jpg" && ext != "xps" && ext != "eml") {

document.getElementById('<%# cvFlpAttach.ClientID %>').innerHTML = "Please upload valid file format (pdf/ppt/rtf/msg/doc/docx/xls/xlsx/jpeg/gif/png/txt/xps/pps/eml) only"

return args.IsValid = false;

}
else if (myIndex > 0) {

document.getElementById('<%# cvFlpAttach.ClientID %>').innerHTML = "Sorry, Invalid characters in filename(#%@&*:<>?\/{|}~).";

return args.IsValid = false;

}

else {

document.getElementById('<%# cvFlpAttach.ClientID %>').innerHTML = "";

return args.IsValid = true;

}

}

}

}