I have one function getTotByMonth in xls file, it is used to calculate total month by month. Ihave to put some condition for some product. to read the product I used below line var pl = plNode.selectSingleNode("root/select").getAttribute("pl");

function getTotByMonth(plNode,nam){
        var total = 0;
        var objectif = plNode.getAttribute("obj");
        var mto = eval(plNode.selectNodes("mto"));
        var pl  = plNode.selectSingleNode("root/select").getAttribute("pl");
        if (pl == "SP") {
        //logic
        }
}


In the javascript line getting below error in this line 

source.selectSingleNode("root/select").setAttribute("pl",savePL);

Microsoft JScript runtime error 'selectSingleNode(...)' is null or not an object line = 100, col = 2 (line is offset from the start of the script block). Error returned from property or method call.

could you please help me to read the product value.