How to use the y-protocols/sync.js.messageYjsSyncStep2 function in y-protocols

const readMessage = (room, buf, syncedCallback) => {
  const decoder = decoding.createDecoder(buf)
  const encoder = encoding.createEncoder()
  const messageType = decoding.readVarUint(decoder)
  if (room === undefined) {
    return null
  }
  const awareness = room.awareness
  const doc = room.doc
  let sendReply = false
  switch (messageType) {
    case messageSync:
      encoding.writeVarUint(encoder, messageSync)
      const syncMessageType = syncProtocol.readSyncMessage(decoder, encoder, doc, room)
      if (syncMessageType === syncProtocol.messageYjsSyncStep2 && !room.synced) {
        syncedCallback()
      }
      if (syncMessageType === syncProtocol.messageYjsSyncStep1) {
        sendReply = true
      }
      break
    case messageQueryAwareness:
      encoding.writeVarUint(encoder, messageAwareness)
      encoding.writeVarUint8Array(encoder, awarenessProtocol.encodeAwarenessUpdate(awareness, Array.from(awareness.getStates().keys())))
      sendReply = true
      break
    case messageAwareness:
      awarenessProtocol.applyAwarenessUpdate(awareness, decoding.readVarUint8Array(decoder), room)
      break
    case messageBcPeerId: {
      const add = decoding.readUint8(decoder) === 1