websocket-js

An abstraction over WebSockets that just works. It keeps the connection alive, self-heals from failures, and provides flexibility with application-level protocol, including the client authentication mechanism.

Installation

npm install @deilux/websocket-js

Motivation

Over the past few years, I’ve had to implement WebSocket communication many times and grew tired of the repetitive boilerplate and chasing edge cases. Many WebSocket libraries were non-starters: too complex and prone to hiding the underlying protocol behind their own abstractions. Cloud-based solutions didn’t fit either — my projects require heavy customization, and at that scale I can build and operate the infrastructure myself.

This library grew out of my work on theshutter.app (@heyshutterapp) — a platform for running remote photoshoots and recording video interviews — which involves a lot of real-time communication over WebSockets and WebRTC.

WsConnectionMonitor

The core of this library is WsConnectionMonitor — a finite state machine that keeps a WebSocket connection alive. It handles reconnection automatically, so you don't have to.

State machine

Disconnected → Connecting → Limbo → Connected
                   ↑                    │
                   └── Reconnecting ←───┘
                         (on error, close, or heartbeat timeout)

• disconnected — initial and terminal state
• connecting — WebSocket is being created
• limbo — transport connected, waiting for application-level handshake
• connected — healthy connection at both transport and application level
• reconnecting — recovering from failure, will retry after delay

Application-level connection

WsConnectionMonitor is protocol-agnostic. When the WebSocket opens, it transitions to limbo and calls your onConnectedFn(). This is where you authenticate, join a room, subscribe to topics, etc. Return true to confirm the connection is ready, which transitions to connected.

If your handshake doesn't complete within connectionTimeout, the connection is considered failed and reconnection is triggered.

Heartbeats

Heartbeat handling is split by responsibility:

• Outbound: WsConnectionMonitor calls your sendHeartbeat(ws, interval) function at heartbeatInterval. You decide what to send (ping frame, JSON message, etc.).

• Inbound: Your application tracks incoming heartbeats. When you detect a missing one, call handleWebSocketHeartbeatTimeout() to trigger reconnection.

This design keeps WsConnectionMonitor unaware of your wire protocol.

WebSocket factory

WsConnectionMonitor doesn't create WebSockets directly. Instead, you provide a createWs() factory function. This allows you to:

• Use custom WebSocket implementations
• Add logging or instrumentation

Configuration

All timing is configurable via the options object:

{
  heartbeatInterval: 15000,  // How often to send outbound heartbeats
  reconnectDelay: 2000,      // Delay before reconnection attempt
  connectionTimeout: 15000,  // Max time to complete handshake in limbo
}

GreatWebSocket

GreatWebSocket is the main class you'll use. It wraps WsConnectionMonitor and adds:

• Convenient send() method with connection checking
• RPC-style request/response via call() and tryHandleAsControlMessage()
• Connection state events

Basic usage

import { GreatWebSocket, ConnectionState } from '@deilux/websocket-js';

const ws = new GreatWebSocket(
  'wss://api.example.com/ws',
  
  // Called when transport connects — do your handshake here
  async () => {
    ws.send(JSON.stringify({ type: 'auth', token: 'my-token' }));
    // Return true when handshake succeeds
    return true;
  },
  
  // Called for every incoming message
  (socket, ev) => {
    const message = JSON.parse(ev.data);
    
    // First, check if it's an RPC response
    if (ws.tryHandleAsControlMessage(message)) {
      return;
    }
    
    // Otherwise, handle as a regular message
    console.log('Received:', message);
  },
  
  // Called periodically to send outbound heartbeat
  (socket, interval) => {
    socket.send(JSON.stringify({ type: 'ping' }));
  },
);

// Listen for state changes
ws.addEventListener('statechange', (ev) => {
  console.log('Connection state:', ev.state);
});

// Start the connection
ws.activate();

// Send messages (returns false if not connected)
ws.send(JSON.stringify({ type: 'hello' }));

// Stop when done
ws.shutdown();

RPC-style commands

Define commands by implementing the RemoteCommand interface:

import { RemoteCommand, GreatWebSocket } from '@deilux/websocket-js';

class JoinRoomCommand implements RemoteCommand {
  private messageId = crypto.randomUUID();
  
  constructor(private roomId: string) {}
  
  execute(ws: GreatWebSocket): string {
    ws.send(JSON.stringify({
      id: this.messageId,
      type: 'join_room',
      roomId: this.roomId,
    }));
    return this.messageId;
  }
  
  responseMatches(message: unknown): boolean {
    return (message as any)?.id === this.messageId;
  }
  
  handleResponse(message: unknown): string {
    return (message as any).status; // Return whatever you need
  }
}

// Usage
const status = await ws.call(new JoinRoomCommand('room-123'));
console.log('Joined with status:', status);

The call() method returns a Promise that resolves when a matching response arrives.