Javascript verifies the attachment size

/// Verify that a single file cannot exceed 30 mb
Function onchangefile ()
{
/// Defines the returned results of the boolean type. The initial value is false (the default value is no more than 30 mb)
VaR sresult = false;
/// Obtain and calculate the attachment size
VaR FSO = new activexobject ("scripting. FileSystemObject ");
VaR fileobj = FSO. GetFile (attachform. upfile. value );
VaR filesize = (fileobj. Size/1024)/1024;
/// Verify whether the attachment size exceeds 30 mb
If (filesize. tofixed (2)> 30)
{
Alert ('file size cannot exceed 30 mb! ');
Sresult = true;
}
Return sresult;
}