The onChange hook is called when the document itself has changed. It should return a Promise.

It's important to understand that this hook is called just once per document. You can use it to react to changes by a specific connection, because we're passing context and update in the payload (see below).

It's highly recommended to debounce extensive operations as this hook can be fired up to multiple times a second.

Hook payload

The data passed to the onChange hook has the following attributes:

import { IncomingHttpHeaders } from 'http'
import { URLSearchParams } from 'url'
import { Doc } from 'yjs'

const data = {
  clientsCount: number,
  context: any,
  document: Doc,
  documentName: string,
  instance: Hocuspocus,
  requestHeaders: IncomingHttpHeaders,
  requestParameters: URLSearchParams,
  update: Uint8Array,
  socketId: string,

Context contains the data provided in former onConnect hooks.


Use a primary storage

The following example is not intended to be your primary storage as serializing to and deserializing from JSON will not store collaboration history steps but only the resulting document. This example is only meant to store the resulting document for the views of your application. For a primary storage, check out the Database extension.

import { debounce } from 'debounce'
import { Server } from '@hocuspocus/server'
import { TiptapTransformer } from '@hocuspocus/transformer'
import { writeFile } from 'fs'

let debounced

const server = Server.configure({
  async onChange(data) {
    const save = () => {
      // Convert the y-doc to something you can actually use in your views.
      // In this example we use the TiptapTransformer to get JSON from the given
      // ydoc.
      const prosemirrorJSON = TiptapTransformer.fromYdoc(data.document)

      // Save your document. In a real-world app this could be a database query
      // a webhook or something else

      // Maybe you want to store the user who changed the document?
      // Guess what, you have access to your custom context from the
      // onConnect hook here. See authorization & authentication for more
      // details
      console.log(`Document ${data.documentName} changed by ${data.context.user.name}`)

    debounced = debounce(save, 4000)