Put this function into User.js:

/**
 *	Check if sheet specified by `sheetName` exists in Excel workbook specified by `fileName`
 */
function CheckExcelSheet(/**string*/fileName, /**string*/sheetName)
{
	var sw = new ActiveXObject("SeSWrappers.Utils.SpreadsheetWrapper");
	var res = sw.Open(fileName);
	
	for(var i=0;i<sw.GetSheetCount();i++) 
	{
		var sn = sw.GetSheetName(i);
		if(SeSCheckString(sheetName, sn)) 
		{
			return true;
		}
	}
	return false;
}

 

Example usage: