Filtering Subgrid using JavaScript and FetchXML

function filterSubGrid() {

  // retrieve the lookup field id
  var lookup = Xrm.Page.getAttribute("new_discipline").getValue();
  var entityid = lookup[0].id.slice(1, -1);
  var entityname = lookup[0].name;
  var entitytype = lookup[0].entityType;

  // testing to console
  console.log("TESTING!! Entity ID: " + entityid);
  console.log("TESTING!! Entity Name: " + entityname);

  // get the subgrid object
  var subgrid = document.getElementById("supportOffers");
  // testing to console
  console.log("TESTING!! Sub Grid: " + subgrid);

  if (subgrid == null){
    setTimeout(function(){
      filterSubGrid();}, 2000);
    return;
  }

  // FetchXML that we want the subgrid to be filtered on including the filter with the entity id of new_discipline
  var fetchXml =
    "<fetch version='1.0' output-format='xml-platform' mapping='logical' distinct='false'>" +
      "<entity name='new_supportoffer'>" +
        "<attribute name='new_supportoffertitle' />" +
        "<attribute name='new_discipline' />" +
        "<attribute name='createdon' />" +
        "<order attribute='new_supportoffertitle' descending='true' />" +
        "<filter type='and'>" +
          "<condition attribute='new_discipline' operator='eq' value='" + entityid + "'" + "/>" +
        "</filter>" +
      "</entity>" +
    "</fetch>";

      //set the fetchxml to the subgrid element
      subgrid.control.SetParameter("fetchXml", fetchXml);
      // refresh the subgrid implementing the new fetchXml
      subgrid.control.refresh();
}