// Adds the supplied item to the list.
AddObject()
{
  const joinOns = new LJCJoinOns();
  let joinOn = joinOns.Add("fromColumnName1", "toColumnName1");
  joinOns.AddObject(joinOn);
  joinOn = joinOns.Add("fromColumnName2", "toColumnName2");
  joinOns.AddObject(joinOn);

  joinOn = joinOns.Retrieve("fromColumnName2");
  let result = joinOn.ToColumnName;

  // result:
  // toColumnName2
}