Variable Undefined When Blank

[Mike]

I am having a problem when a field on the spreadsheet is blank. I
should be getting an error message passed back to the screen telling
the user that the field is blank. But instead I am getting an error
message that points to another field that has been filled in.

The users are able to select from a drop down list either a
pre-existing Excel spreadsheet or a blank spreadsheet where they can
enter the data. When they click the Store button, I am using
Javascript to validate the fields. If a particular field is not
entered or has invalid data, then an error message will appear on the
screen. In this case, I was testing for a blank field and did not get
the error message I was expecting. So I put in some Response.Write
statements to display what was in the field and in this case this is
where it showed up as undefined. If there is data in the field, then
the field displays correctly. The following is an example of the code:

do
{
indexRow+=1;
}
while (mExcelApp.ActiveSheet.Cells(indexRow, 1) != "RECORD");
indexRow+=2;

RecordCount = 0;

do
{

var xlSourceDoc = mExcelApp.ActiveSheet.Cells(indexRow, 2);
var xlRefNumber = mExcelApp.ActiveSheet.Cells(indexRow, 3);
var xlFYR = mExcelApp.ActiveSheet.Cells(indexRow, 4);
var xlClass = mExcelApp.ActiveSheet.Cells(indexRow, 5);
var xlNNNNN = mExcelApp.ActiveSheet.Cells(indexRow, 6);
var xlAAAA = mExcelApp.ActiveSheet.Cells(indexRow, 7);
var xlLLLL = mExcelApp.ActiveSheet.Cells(indexRow, 8);
var xlFFF = mExcelApp.ActiveSheet.Cells(indexRow, 9);
var xlLineDollarAmt = mExcelApp.ActiveSheet.Cells(indexRow, 10);
var xlLineUnits = mExcelApp.ActiveSheet.Cells(indexRow, 11);
var xlLineDesc = mExcelApp.ActiveSheet.Cells(indexRow, 12);

if ((xlSourceDoc == "") || (xlSourceDoc == null) || (xlSourceDoc
== "undefined"))
{
mError = 11;
mResults = showErrorMsg();
break;
}

if ((xlRefNumber == null) || (xlRefNumber == "undefined") ||
(xlRefNumber == ""))
{
mError = 12;
mResults = showErrorMsg();
break;
}

var xlFYRStr = String(xlFYR);
var xlFYRFirstChar = xlFYRStr.substr(0, 1);
var xlFYRLastTwoChar = xlFYRStr.substr(1, 2);

if (xlFYRFirstChar == "f" ||
xlFYRFirstChar == "p" ||
xlFYRFirstChar == "F" ||
xlFYRFirstChar == "P" ||
xlFYRFirstChar == "")
{
return true;
}
else
{
mError = 13;
mResults = showErrorMsg();
break;
}
<code trimmed>

RecordCount+=1;
indexRow+=1;
}
while (RecordCount < xlRecCnt);

In showErrorMsg() is where I have my error messages defined and mError
= xx
returns a particular message. In this instance of my testing, I left
xlSourceDoc blank and should get error message #11. But instead I am
getting the error message #13, associated with the xlFYR field.

Being fairly new to both Excel and Javascript, I am at a lost as to
how to correct the problem. Does anyone have an idea what I need to
do? TIA for any help!

Mike