Returns the item id of the item in the specified inventory slot

itemId = GetInventoryItemID("unit", invSlot);

Arguments

unit 

String - The UnitId of the unit whose inventory is to be queried.

invSlot 

Number (InventorySlotId) - index of the inventory slot to query.

Returns

itemId

Number - item id of the item in the inventory slot; nil if there is no item.