Yjs/community

@dmonad I'm running into an issue with using yjs for a collaborative text editing tool. When I inspect the IndexedDB database, it appears that the initial state update is getting stored twice. The documents can be quite large, so I don't want to waste all of this space.

That said, I'm trying to understand encodeStateAsUpdate's second parameter, as it appears to exist to mitigate this issue, but it isn't operating the way I expect. My understanding is that if you supply the same state as the target object, you should get a very small or nonexistent update, but that's not happening.

Example code for testing:

const docA = new Y.Doc();
const docB = new Y.Doc();

docB.on('update', (update: Uint8Array) => {
  console.log('update', update);
});

docA.getMap().set('name', new Y.Text('El Pollo Diablo'));
docB.getMap().set('name', new Y.Text('El Pollo Diablo'));

const docBState = Y.encodeStateVector(docB);
const update = Y.encodeStateAsUpdate(docA, docBState);

console.log('before update');
Y.applyUpdate(docB, update);
console.log('after update');

console.log(docA.getMap().toJSON());
console.log(docB.getMap().toJSON());

Output:

update Uint8Array(42) [
    1,   2, 168, 154, 142, 211,   8,   0, 39,   1,
    0,   4, 110,  97, 109, 101,   2,   4,  0, 168,
  154, 142, 211,   8,   0,  15,  69, 108, 32,  80,
  111, 108, 108, 111,  32,  68, 105,  97, 98, 108,
  111,   0
]
before update
update Uint8Array(50) [
    1,   2, 152, 205, 189, 164,   9,   0,  39,   1,   0,
    4, 110,  97, 109, 101,   2,   4,   0, 152, 205, 189,
  164,   9,   0,  15,  69, 108,  32,  80, 111, 108, 108,
  111,  32,  68, 105,  97,  98, 108, 111,   1, 168, 154,
  142, 211,   8,   1,   0,  16
]
after update
{ name: 'El Pollo Diablo' }
{ name: 'El Pollo Diablo' }