bind-socketio-handlers

Overview

On each client connection to a socket.io server, this library binds events received on the client socket to handler functions.

It also provides convenient helper methods to those helper functions.

Usage

// handlers.js
export const sayHello = (callbacks, io, socket) => // handle event

// express.js
import express from 'express';
import socketIo from 'socket.io';
import bindSocketIoHandlers from 'bind-socketio-handlers';
import * as handlers from './handlers';

const onClientConnect = io => socket => {
  bindSocketIoHandlers(io, socket, handlers);
};

const app = express();
const io = socketIo(app);
io.on('connection', onClientConnect(io));

Callbacks

The callbacks object passed to each handler contains some helper functions:

{
  toSocket(event, payload),
  toRoom(roomName)(event, payload),
  joinRoom(roomName),
  leaveRoom(roomName),
  emitError(e, parameters),
  onError(e, parameters), // alias for emitError
}

All default callback functions return a promise that resolve to undefined.

You can extend or over-write these callbacks by passing an object of named callback functions to bindSocketIoHandlers:

  const myCallbacks = (socket) => ({
    sayHiBack: () => socket.emit('Hi, back.'),
  });
  bindSocketIoHandlers(io, socket, handlers, myCallbacks(socket));

These methods will then be accessible along with the default callbacks in your handler function:

// handlers.js
export const sayHello = ({ sayHi }) => sayHi();

Error handling

If your handler returns a promise that rejects, or if it throws an error, the client socket will be sent an event of type 'applicationError', with the error message as a payload:

// handlers.js
export const sayHello = ({ sayHi }) => Promise.reject(new Error('not today, thanks'));

will result in:

socket.emit('applicationError', { message: 'not today, thanks' });