ok, after a lot of trial and error i have come to an answer that works:
var w =new ActiveXObject("Excel.Application");
var book = w.Workbooks.Open(excelFile);
var ExcelSheet= book.Sheets;
var sheetCount = ExcelSheet.Count;
var arrayOfSheets = new Array();;
for(var i=0;i<sheetCount;i++){
alert("Read sheets from file :"+ExcelSheet.Item(i+1).Name);
arrayOfSheets [i] =ExcelSheet.Item(i+1).Name;
}