如何在json对象中获取数组的大小

Question

这是我的json对象

我需要获取itemDetails数组对象的长度， 我正在使用

for (var i = 0; i < data[0].itemDetails.length; i++) {
                itmCode = "it001";
                itmName = "soap";
                Qty = "4";
                //netAmt = parseFloat(data[i].Net_Amt).toFixed(2);
                //paidAmt = parseFloat(data[i].Paid_Amt).toFixed(2);
                //balance = (parseFloat(netAmt) - parseFloat(paidAmt)).toFixed(2); //id = "damt['+i+']"
                $("#invoiceDetailTbl tbody").append("<tr id=" + i + ">" + "<td>" + itmCode + "</td>" + "<td>" + itmName + "</td>" + "<td>" + Qty + "</td>" + "</tr>");
                noOfItems = parseInt(noOfItems) + parseInt(Qty);
                noOfProducts = parseInt(noOfProducts) + 1;
            }

但总是得到0作为长度