How to use Liveblocks multiplayer undo/redo with Redux

In this guide, we’ll be learning how to use Liveblocks multiplayer undo/redo with Redux using the APIs from the [@liveblocks/redux][] package.

Multiplayer undo/redo

Implementing undo/redo when multiple users can edit the app state simultaneously is quite complex!

When only one user can edit the app state, undo/redo acts like a "time machine"; undo/redo replaces the current app state with an app state that was already be seen by the user.

When multiple users are involved, undo or redo can lead to an app state that no one has seen before. For example, let's imagine a design tool with two users editing the same circle.

  • Initial state => { radius: "10px", color: "yellow" }
  • User A sets the color to blue => { radius: "10px", color: "blue" }
  • User B sets the radius to 20px => { radius: "20px", color: "blue" }
  • User A realizes that it prefered the circle in yellow and undoes its last modification => { radius: "20px", color: "yellow" }

A yellow circle with a radius of 20px in a completely new state. Undo/redo in a multiplayer app does not act like a "time machine"; it only undoes local operation.

The good news is that room.history.undo and room.history.redo takes that complexity out of your hands so you can focus on the core features of your app.

Access these two functions from the client like below so you can easily bind them to keyboard events (⌘+Z/⌘+⇧+Z on Mac and Ctrl+Z/Ctrl+Y on Windows) or undo and redo buttons in your application..

const { undo, redo } = client.getRoom("room-id").history;

Pause and resume history

Some applications require skipping intermediate states from the undo/redo history. Let's consider a design tool; when a user drags a rectangle, the intermediate rectangle positions should not be part of the undo/redo history. But they should be shared with the rest of the room to create a great experience.

room.history.pause and room.history.resume lets you skip these intermediate states. To go back to our design tool example, the sequence of calls would look like that:

  • User presses the rectangle
  • Call room.history.pause to skip future operations from the history
  • User drags the rectangle
  • User release the rectangle
  • Call room.history.resume

At this point, if the user calls room.history.undo, the rectangle will go back to its initial position.

const { pause, resume } = client.getRoom("room-id").history;