Flexible Socket.IO middleware for Redux applications

Usage no npm install needed!

<script type="module">
  import duxSocket from 'https://cdn.skypack.dev/dux-socket';



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Flexible WebSocket middleware for Redux applications. Maps inbound WebSocket events to Redux actions. Exposes action creators for dispatching actions that should be emitted as socket messages. Works with Socket.IO, as well as native WebSocket implementations!


npm install dux-socket



In your project, define a mapDispatchToSocket function, which will receive store.dispatch as its argument, and return an object which maps socket events to arbitrary Redux actions:

const mapDispatchToSocket = (dispatch) => ({
    'eventName': (eventData) => dispatch({type: 'SOME_ACTION', data: eventData}),
    // using action creators
    'otherEvent': (eventData) => dispatch(someAction(eventData)),

This works exactly like the mapDispatchToProps function you are used to from React-Redux's connect API. The functions defined in this map will be invoked with the socket event payload as the argument.

When creating your store & applying middleware, add socketMiddleware in the usual way, supplying the mapDispatchToSocket function defined above, & an initialized Socket object:

import {createStore, applyMiddleware} from 'redux';
import io from 'socket.io-client'
import {socketMiddleware} from 'dux-socket';

const socket = io('http://socket-url');

const store = createStore(
        /* ... other middlewares here ... */
        socketMiddleware(mapDispatchToSocket, socket)

Emitting socket events

Simply dispatch using the emit(eventName, data) action creator supplied by dux-socket in order to emit a socket event:

import {emit} from 'dux-socket';

dispatch(emit('someAction', {foo: bar}))

Native WebSockets

Since native WebSocket implementations don't have a concept of named events, your mapDispatchToSocket function, and the way you send data work a bit differently. Simply supply functions for the native WebSocket event handlers onopen, onmessage, and onerror where relevant to your application, and map them to Redux actions however you see fit:

import {socketMiddleware} from 'dux-socket';
import {createStore, applyMiddleware} from 'redux';

let socket = new WebSocket('ws://localhost:4242');

const mapDispatchToSocket = (dispatch) => ({
  'onmessage': (event) => dispatch({ type: 'CHAT_MESSAGE', message: event.data }),
  'onerror': (event) => dispatch({ type: 'ERROR', msg: 'Connection error!' })

const store = createStore(
  applyMiddleware(socketMiddleware(mapDispatchToSocket, socket))

Sending text data

Use the send(data) action creator to send data over a native WebSocket connection.

import {send} from 'dux-socket';

dispatch(send('some data!'))

Asynchronous socket initialization

You may want to include some asynchronously-resolved data (ie. route parameters) in your initial connection with the WebSocket server. To do this, simply don't supply a WebSocket object when applying the socketMiddleware:

const store = createStore(

And dispatch an initSocket event when you are ready to initialize the socket! Supply this action creator with either a Socket.IO object or a native WebSocket object.

import io from 'socket.io-client'
import {initSocket} from 'dux-socket';
import store from '../store';

class SomeComponent extends Component {
    componentDidMount() {
        let socket = io('http://socket-url', { foo: 'bar' });


Flexibility! The main goals for a flexible Redux/WebSocket middleware are:

  1. Event-agnostic: You should be able to integrate an existing Redux application with an existing WebSocket server without re-writing your server-initiated events or your client-side reducers.
  2. Asynchronous: You should be able to (optionally) initialize your web socket connection asynchronously. This is useful if you want to include some resolved data in your handshake with the web socket server, (ie. router parameters)
  3. Native WebSocket support: You should be able to (optionally) use a native WebSocket implementation, in case you don't want to use Socket.IO

Other middleware libraries emit a single Redux action for all Socket events. This leads to tightly coupled reducers & nested branching over the event types within your reducer cases. dux-socket solves this problem by invoking client-defined actions according to the map provided:

Redux Architecture Approaches


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