identifiers.md

Identifiers (ids)

Draggable > draggableId and Droppable > droppableId

A Draggable and a Droppable have an id. These are draggableId and droppableId respectively.

String

We expect an id to be a string

type Id = string;
type DroppableId = Id;
type DraggableId = Id;

More information: types guide

Ids must be unique

A id must uniquely identify a Draggable or Droppable within a DragDropContext. So if you have multiple connected lists, each Droppable needs to have a unique id and each Draggable needs to have a unique id, even if the item is in a different list.

The id must also be unique event if the type argument on the Droppable is different.

Avoid reusing ids

For simplicity, it is best to avoid changing a draggableId or droppableId when a reorder occurs. The safest option is to associate an id with an piece of data and do not update the id between reorders.

You can change the draggableId or droppableId at any time except during a drag. Including after reorder. However, to avoid an exception you need to avoid reusing id's between two components. This can happen if you base a draggableId or droppableId on an index.

Don't base an id on a index

What this looks like internally

1. Update droppable

old droppableId: "droppable-0" new droppableId: "droppable-1"

👉 delete reference to "droppable-0" 👉 add reference to "droppable-1"

2. Update droppable

old droppableId: "droppable-1" 😢 new droppableId: "droppable-2"

👉 delete reference to "droppable-1" 😢 (will remove reference to our new "droppable-1") 👉 add a reference to "droppable-2"

3. Update droppable

old droppableId: "droppable-1" 💥 new droppableId: "droppable-5"

👉 delete reference to "droppable-1" 💥 (will cause an exception because "droppable-1" is not found)

Could we change these rules?

Yep!

But we do things this way for simplicity and performance. Feel free to continue this conversation in a Github issue if you feel strongly about it.