js文件大小，类型判断

<script>

function ValidateFileSize(FilePath,FileMaxSize,fileExt){

var ValidateFileSize="";
if(FilePath==""){

        ValidateFileSize = "-2";

        return ValidateFileSize;
}
if(fileExt != ""){
var ext = fileExt.split(",");
var index1=FilePath.lastIndexOf(".");

        var index2=FilePath.length;

        var suffix=FilePath.substring(index1+1,index2);

        var j=0;
for(var i=0;i<ext.length;i++){
if(suffix==ext[i]){
j=j+1;
}
}
if(j==0){
ValidateFileSize = "-3";
return ValidateFileSize;
}
}
if(FileMaxSize != ""){
var fso = new ActiveXObject("Scripting.FileSystemObject");

         var size = fso.GetFile(FilePath).size;

         if(size==0){

        ValidateFileSize = "0";

        return ValidateFileSize;

         }

         if(size>FileMaxSize){

        ValidateFileSize = "2";

        return ValidateFileSize;

         }
}

function upload()

{
var form = document.getElementById("uploadForm");
var file = document.getElementById("file").value;

var fileValidateResult = ValidateFileSize(file,5242880,"txt,xls");
switch (fileValidateResult)
{
case "-3":
top.jQuery.alerts.alert('只支持TXT,XLS文件格式.');
return;

case "-2":
top.jQuery.alerts.alert('未选择本地文件.');
return;
case "-1":
top.jQuery.alerts.alert('本地文件已经不存在，可能被删除.');
return;
case "0":
top.jQuery.alerts.alert('上传的文件内容不允许为空.');
return;
case "2":
top.jQuery.alerts.alert('上传的文件不能大于5M.');
return;

}

top.lockScreenWait('show');
form.submit();

}

</script>