Fork of express-ws. WebSocket endpoints for Express applications (uses require instead of import, binds routes to the web socket instance, and has high-level support for broadcast client filtering/“room” support).

Usage no npm install needed!

<script type="module">
  import smallTechExpressWs from 'https://cdn.skypack.dev/@small-tech/express-ws';


@small-tech/express-ws (fork)

This fork uses native Node requires (CommonJS) instead of upstream’s ES6 imports (ESM).

Please note that I’ve contributed all changes in this fork (apart from the ESM → CommonJS changes) back upstream in the following unmerged pull request.

Here’s why I hacked together this fork:

  • I needed to include my changes from my git repository.
  • To do so, I needed to build it and the build process wasn’t documented.
  • I don’t want to use Babel and add a build process for a simple library.
  • Without Babel it was causing errors in Nexe due to the additional complexity in module loading.
  • ES6 imports in Node.js… Y, tho? :)

If these are not concerns for you, and if you don’t need references to the WebSocket instance from your routes or broadcast client filtering (“room” functionality), please head on over to the upstream. If you npm install it instead of including it from source, the issues I outlined above should not affect you.


npm install @small-tech/express-ws


In addition to using require() instead of ES6 imports, this fork also enables you to access the WebSocket Server instance and the Express app instance from within routes via this:

app.ws('/broadcast', function(ws, req) {

  ws.on('message', message => {
    this.getWss().clients.forEach(client => {

Note that if you have multiple web socket routes, the above example will broadcast the message to all clients, not just those connected to the /broadcast route.

Note that this list will include all clients, not just those for a specific route - this means that it's often not a good idea to use this for broadcasts, for example. For broadcasts, use the setRoom() and broadcast() methods as shown in the chat example:

const express = require('express');
const expressWs = require('express-ws')(express());

const app = expressWs.app;

function roomHandler(client, request) {
  client.room = this.setRoom(request);
  console.log(`New client connected to ${client.room}`);

  client.on('message', (message) => {
    const numberOfRecipients = this.broadcast(client, message);
    console.log(`${client.room} message broadcast to ${numberOfRecipients} recipient${numberOfRecipients === 1 ? '' : 's'}.`);

app.ws('/room1', roomHandler);
app.ws('/room2', roomHandler);

app.listen(3000, () => {
  console.log('\nChat server running on http://localhost:3000\n\nFor Room 1, connect to http://localhost:3000/room1\nFor Room 2, connect to http://localhost:3000/room2\n');

A note on route scope

Routes are bound to the wsInstance so you can access .getWss(), .setRoom(), .broadcast() and .app via this in your routes even if the original wsInstance is not in scope (e.g., if you have your routes defined in external files).


This module is written in ES6 and uses native Node.js requires (CommonJS) unlike upstream which uses ESM. Among other things, it means that you can wrap apps that use this module into native binaries using Nexe.


Commits up to and including 8efedd5d0946f23c7e386ce44586a7e384a1635c are licensed under BSD-2-Clause by the original author. Commits from and including 18a8d15ef8e63e601ee723d09fd435dd1ee2bed9 are licensed under AGPL version 3.0 or later.

We now return to the regular upstream documentation…

WebSocket endpoints for Express applications. Lets you define WebSocket endpoints like any other type of route, and applies regular Express middleware. The WebSocket support is implemented with the help of the ws library.


npm install --save express-ws


Full documentation can be found in the API section below. This section only shows a brief example.

Add this line to your Express application:

var expressWs = require('express-ws')(app);

Important: Make sure to set up the express-ws module like above before loading or defining your routers! Otherwise, express-ws won't get a chance to set up support for Express routers, and you might run into an error along the lines of router.ws is not a function.

After setting up express-ws, you will be able to add WebSocket routes (almost) the same way you add other routes. The following snippet sets up a simple echo server at /echo. The ws parameter is an instance of the WebSocket class described here.

app.ws('/echo', function(ws, req) {
  ws.on('message', function(msg) {

It works with routers, too, this time at /ws-stuff/echo:

const router = express.Router();

router.ws('/echo', function(ws, req) {
  ws.on('message', function(msg) {

app.use("/ws-stuff", router);

Full example

const express = require('express');
const app = express();
const expressWs = require('express-ws')(app);

app.use(function (req, res, next) {
  req.testing = 'testing';
  return next();

app.get('/', function(req, res, next){
  console.log('get route', req.testing);

app.ws('/', function(ws, req) {
  ws.on('message', function(msg) {
  console.log('socket', req.testing);



expressWs(app, server, options)

Sets up express-ws on the specified app. This will modify the global Router prototype for Express as well - see the leaveRouterUntouched option for more information on disabling this.

  • app: The Express application to set up express-ws on.
  • server: Optional. When using a custom http.Server, you should pass it in here, so that express-ws can use it to set up the WebSocket upgrade handlers. If you don't specify a server, you will only be able to use it with the server that is created automatically when you call app.listen.
  • options: Optional. An object containing further options.
    • leaveRouterUntouched: Set this to true to keep express-ws from modifying the Router prototype. You will have to manually applyTo every Router that you wish to make .ws available on, when this is enabled.
    • wsOptions: Options object passed to WebSocketServer constructor. Necessary for any ws specific features.

This function will return a new express-ws API object, which will be referred to as wsInstance in the rest of the documentation.


This property contains the app that express-ws was set up on.


Returns the underlying WebSocket server/handler. You can use wsInstance.getWss().clients to obtain a list of all the connected WebSocket clients for this server.


Sets up express-ws on the given router (or other Router-like object). You will only need this in two scenarios:

  1. You have enabled options.leaveRouterUntouched, or
  2. You are using a custom router that is not based on the express.Router prototype.

In most cases, you won't need this at all.