How to inspect a Y.Doc update

1

doc.on('update',...) can be used to detect changes within a given Y.Doc.

Is it possible to find out (from this update event) which “shared type” has been changed (and, perhaps, in what way)? And, if yes, how?

Or will I always have to observe every “shared type” individually?

2

It may be possible to extract the shared types from transaction.change, provided as the fourth parameter to the update event handler.

You might also consider observeDeep on a root Y.Map.

3

oh, there is a fourth parameter? good to know, thanks!

4

The secret fourth parameter. Advanced users only! :wink:

5

Damn…I’m still a Yjs newbie

6

Oh, I misunderstood - I know the transaction parameter - and already inspected its changed property, but that structure seems to lack important information (such as the name of the top-level Y.Doc entry that was changed…

[Edit] the key of a transaction.changed entry seems to be the changed structure itself?

7

I’m not sure. Usually I do shared-type specific behavior in the observe or deepObserve events, not the update event.

8

by the way: I am now able to inspect updates to top-level Y.Maps, but not to top-level Y.Arrays or Y.Texts

observe and deepObserve work on Y.Doc entries only, not on Y.Docs themselves.

For scalability reasons, I would prefer a single handler for the main Y.Doc rather than many handlers for every single Y.Doc entry or SubDoc…

If you want to see some code:

  const sharedDoc = new Y.Doc()
    sharedDoc.on('update',(Update,Origin,Doc,Transaction) => {
      console.log('new transaction')
      Transaction.changed.forEach((ChangeSet,Container) => {
        if (
          (Container instanceof Y.Map) ||
          (Container._map instanceof Map) && (Container._map.size > 0)
        ) {
          console.log('- Y.Map:')
          ChangeSet.forEach((Value,Key) => {
            console.log('  -',Key,'=',Value)
          })
          return
        }

        if (
          (Container instanceof Y.Array) ||
          (Container._start != null) && ('arr' in Container._start.content)
        ) {
          console.log('- Y.Array:',Transaction)
          return
        }

        if (
          (Container instanceof Y.Text) ||
          (Container._start != null) && ('str' in Container._start.content)
        ) {
          console.log('- Y.Text:',Transaction)
          return
        }

        if (
          (Container instanceof Y.XmlFragment) ||
          (Container._start != null) && ('type' in Container._start.content)
        ) {
          console.log('- Y.XmlFragment:',Transaction)
          return
        }

        console.log('Transaction',Transaction)
      })
    })

Those strange type detection expressions are needed since updates from a provider seem to look different than updates from business logic…(sigh)

9

If you have a single root Map, it’s only a one observeDeep for all shared types.

transaction.origin might help you differentiate transactions originating on a local doc (which is usually set to doc.clientID) and transactions synced over a provider (which is usually set to the provider instance).

10

Indeed,

while Y.Doc look a bit like (top-level) maps with an additional sub-doc registry, it might be better to always add a first indirection in form of a top-level Y.Map or Y.Array which could then be (deeply) observed more easily…

11

Yes. Unfortunately subdoc support is severely lacking. But nested shared types work well across providers.