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A lightweight non-opinionated NPM library that offers a custom React hook that utilizes websockets to synchronize state between multiple clients and can evolve state dynamically, coupled with a server side NPM library containing a handler to receive messages from the hook on a websocket server which persists the state updates on a database and notifies clients of changes.

1. npm install socket-league-client for access to the custom React hook.
2. npm install socket-league-server for access to the websocket server handler.

Let's break down the components of the call to explain each part of the hook invocation.

The Connection class wraps all the front-end logic to manage the hook. It should be initialized with the URL of the websocket server with which the client will be communicating state, and which will be sending state updates to the client. Under the hood, the Connection class automatically reconnects using the Reconnecting WebSocket library.

Our library gives developers the flexibility to transmit any data to represent the state in the hook. The hook anticipates that the communication protocol between server and client includes the entire state, not just incremental updates.

The session ID is how clients subscribe to state updates from the server when the server receives an update. The first time a session ID is received by the server, it saves the received state in the database. Otherwise, it updates the client with the already saved state information on the database instead.

The Connection class sends three message types to the server: Initial, Update, and Undo.

1. Initial: This message type is the first message sent when the Connection object first contacts the server. The first time a session ID is received by the server, it saves the received state in the database. Otherwise, it updates the client with the already saved state information on the database instead.
2. Update: After a websocket connection is established, any updates to the application state are transmitted to the server via the custom React hook through Update messages. Each reception of an Update message by the server causes the server to emit updates to all clients associated with that Update message's session ID
3. Undo: This message type notifes the server to delete the last state associated with the included session ID and transmit the last prior state associated with session ID to the client. This behavior can be customized Nothing will happen if the state is regressed to the point of initial contact with the first client to initialize the earliest state associated with that session ID.
4. Unsubscribe: This message type notifies the server to stop sending updates to the client associated with the session included in the subsubscribe message.

Finally, to add the custom hook to the application, simply invoke useSyncState with the desired session ID, the desired initial state, a Connection object, and the local version of React.

The version of React should be passed into useSyncState in order to avoid versioning and dependency issues.

  //outside the React component's render or return method
  const conn = new Connection ('ws://localhost:3000');

  //within the React component's render or return method
  const [socketState, setSocketState, undoSocketState] = useSyncState(
    session,
    initialState,
    conn,
    React
  );

A SyncHandler object should be instantiated with the database driver in which the state is to be tracked. If no database driver is specified, the default database driver will use JSON to track state.

Currently MongoDB and PostgresSQL are supported by pre-designed drivers. The TypeScript interface driver.ts provides the specifications for other drivers to implement.

Example 1: Instantiating the SyncHandler with MongoDB or Postgres as the database storing state.

const syncHandler = new SyncHandler(new MongoDriver(`myURI`)); const syncHandler = new SyncHandler(new PostgresDriver(`myURI`));

Example 2: Instantiating the SyncHandler with a JSON database.

const syncHandler = new SyncHandler(); is equivalent to const syncHandler = new SyncHandler(new JsonDriver());

The SyncHandler does not automatically connect to the database driver provided on its invocation.syncHandler.connect() should be used to initialize the asynchronous database connection. If the connected database driver is changed, syncHandler.connect() should be called again.

Finally, the SyncHandler object should be invoked during connection events for the websocket server implementation.

Below is the sample implementation for the ws library.

const syncHandler = new SyncHandler();
await syncHandler.connect();
const wsServer = new ws.Server({ noServer: true });
wsServer.on("connection", syncHandler.handleWsConnection);

By default, the SyncHandler automatically disconnects websockets that reach the close state while connected. This behavior can be changed by invoking the toggleAutoDisconnect() method.

const syncHandler = new SyncHandler();
console.log(syncHandler.toggleAutoDisconnect()); //returns and logs the current AutoDisconnect status.

By default, the database preserves only the most recently received state. This behavior can be customized using the StateMerger class.

The properties of the merger can be accessed by calling .merger on the SyncHandler.

1. setDefaultHandler can be used to set custom behavior for conflicting states, for example by diffing or calculating which state to keep.

const syncHandler = new SyncHandler();
syncHandler.merger.setDefaultHandler((serverState, oldState, newState) => Math.max( serverState + oldState, serverState + newState));

2. registerHandler can be used to set custom behavior for conflicting states, but only for specific sessions, if the conflict management behavior is only desired in specific cases.

const syncHandler = new SyncHandler();
syncHandler.merger.registerHandler( '0', (serverState, oldState, newState) => Math.max( serverState + oldState, serverState + newState) );

The SyncHandler can preprocess inputs received from clients for validity or encryption purposes.

A function can be set for this purpose by invoking setProcessState(), which takes as a parameter the helper function containing the logic to process the state.

This helper function should take one parameter representing an object containing keys of state, session, and action type, as well as the oldState if applicable, and return the processed object containing those same keys.

const syncHandler = new SyncHandler();
syncHandler.setProcessState( (stateUpdate) => {console.log(stateUpdate.session), return stateUpdate} );

The helper function set using setProcessState() can be cleared by invoking resetProcessState().

syncHandler.resetProcessState();

Check out our chat-app we built using our very own NPM libraries and hooks!

Our Echo Server is a chat application with four separate channels for conversation. Clients are synchronized to the server via websockets, which transmit updates relating to any messages sent or background changes. Feel free to cruise around and see how exactly it all comes together.

We'd love for you to test this library out and submit any issues you encounter. Also feel free to fork to your own repo and submit pull requests!

Aaron Gaut Kyle Boudewyn Kurt Crandall Trevor Mow Zachary Lim