code: function requestSlot(slot) {
                      // Ensure that there's a slot on either side of each requested item
                      if (slot.firstInSequence) {
                          addSlotBefore(slot, indexMap);
                      }
                      if (slot.lastInSequence) {
                          addSlotAfter(slot, indexMap);
                      }
  
                      // If the item has already been fetched, prepare it now to be returned to the client
                      if (slot.itemNew) {
                          prepareSlotItem(slot);
                      }
  
                      // Start a new fetch if necessary
                      postFetch();
  
                      return slot;
                  }
docs: Item Requests