Error when moving an YMap item inside YArray

1

Hi,

I get an unexpected error when moving an YArray item, when the item is a YMap. The idea is to remove an item and then re-insert it into another position, but the problem can be re-produced with the following snippet of code:

  const ydoc = new Y.Doc();
  const items = ydoc.getArray("items");
  items.push([new Y.Map(), new Y.Map()]);
  const removedItem = items.get(0);
  items.delete(0);
  items.push([removedItem]);

When pushing the removed item back into the array, I get an error like

Uncaught TypeError: Cannot read properties of null (reading 'forEach')
    at YMap._integrate (yjs.cjs:6005:60)
    at ContentType.integrate (yjs.cjs:9387:15)
    at Item.integrate (yjs.cjs:9948:20)
    at eval (yjs.cjs:5394:22)
    at Array.forEach (<anonymous>)
    at typeListInsertGenericsAfter (yjs.cjs:5367:11)
    at typeListPushGenerics (yjs.cjs:5477:10)
    at eval (yjs.cjs:5828:9)
    at transact (yjs.cjs:3416:14)
    at YArray.push (yjs.cjs:5827:7)

You can see it in action in this CodeSandbox: https://codesandbox.io/p/sandbox/yjs-move-array-item-f7tvvj?file=%2Fsrc%2FApp.tsx%3A19%2C24

If I use strings instead of YMaps as items, there are no errors. Is there something special I should do in order to be able to re-insert a Y.Map into an array?

Thanks for Y.js btw, it’s awesome! Hoping to be able to contribute at some point, still learning the ropes.

2

Having looked at source code it seems to me that the “integration” of a YMap or YArray to a YDoc is a one-way process and there’s no way to “un-integrate” or “re-integrate” if I’ve understood correctly. Does this mean that I am to change the ordering of (YMap or YArray) elements in a list, I’ll practically have to treat the moved content as new content? This would be bad for collaborative editing of nested data of course.

By treating as new content, I mean that I would practically insert a new YMap with identical content to the original one. And if the moved item is a deep hierarchical structure of YMaps and YArrays, I would have to traverse the graph and create a deep clone. Sounds suboptimal for changing item ordering :sweat_smile: