Yjs Middleware for Zustand

One of the difficult things about using Yjs is that it's not easily integrated with modern state management libraries in React. This middleware for Zustand solves that problem by allowing a Zustand store to be turned into a CRDT, with the store's state replicated to all peers.

This differs from the other Yjs and Zustand solution, zustand-yjs by allowing any Zustand store be turned into a CRDT. This contrasts with zustand-yjs's solution, which uses a Zustand store to collect shared types and access them through special hooks.

Because this solution is simply a middleware, it can also work anywhere Zustand can be used. The vanilla Zustand create() function handles middleware exactly the same as the React version. And not only that, but it can be composed with other middleware, such as Immer or Redux!

Example

import React from "react";
import { render } from "react-dom";

import * as Y from "yjs";
import create from "zustand";
import yjs from "zustand-middleware-yjs";

// Create a Y Doc to place our store in.
const ydoc = new Y.Doc();

// Create the Zustand store.
const useSharedStore = create(
  // Wrap the store creator with the Yjs middleware.
  yjs(
    // Provide the Y Doc and the name of the shared type that will be used
    // to hold the store.
    ydoc, "shared",
          
    // Create the store as you would normally.
    (set) =>
      ({
        count: 0,
        increment: () =>
          set(
            (state) =>
            ({
              count: state.count + 1,
            })
          ),
      })
  )
);

// Use the shared store like you normally would any other Zustand store.
const App = () =>
{
  const { count, increment } = useSharedStore((state) =>
    ({
      count: state.count,
      increment: state.increment
    }));

  return (
    <>
      <p>count: {count}</p>
      <button onClick={() => increment()}>+</button>
    </>
  );
};

render(
  <App />,
  document.getElementById("app-root")
);

Caveats

1. Currently the Y Text shared type is not supported. This means that strings in the store do not benefit from the conflict-resolution performed by Yjs.
2. The Yjs awareness protocol is not supported. At the moment, it is unclear if the library is able to support Yjs protocols. This means that, for now, support for the awareness protocol is not planned.

License

This library is licensed under the MIT license:

Copyright © 2021 Joseph R Miles

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.