How do I get the relationship name from a HTML grid

Below is my code. I'm trying to get the name from the itemtype User where the created_by_id.

 

for (var j = 0; j < itms.getItemCount(); j++) {

var itm = itms.getItemByIndex(j);

var id = itm.getAttribute("id");

valsArr = [itm.getProperty("item_number", ""),itm.getProperty("created_by_id", "")];

(var k = 0; k < valsArr.length; k++) {

if (!valsArr[k]) valsArr[k] = "";