Web socket servers

INFO

Although web sockets aren't specific to Express, this part of the docs focuses heavily on servers, so we felt these notes belonged here.

Creating a web socket server

To create a web socket server, we first install the ws library:

npm install ws

Then, in app.js we import and use the WebSocketServer class from ws.

import { WebSocketServer } from 'ws'

const server = new WebSocketServer({ port: 5001 })

Listening for connections

It is very simple to listen for new connections.

import { WebSocketServer } from 'ws'

const server = new WebSocketServer({ port: 5001 })

server.on('connection', (socket) => {
  // do what we want with the socket
})

When the 'connection' event is emitted, we are passed a web socket, which we can call whatever we want (here, we used socket).

Listening for socket events

Now we have a socket, we can handle new messages which arrive from the client.

import { WebSocketServer } from 'ws'

const server = new WebSocketServer({ port: 5001 })

server.on('connection', socket => {
  socket.on('message', handleMessage)
  socket.on('close', cleanUp)
})

Sending a message back

At any time we choose, we can send a message back to the client simply using the .send method:

socket.send('Hello from the server!')

The client will immediately have access to the message, provided it hasn't closed the connection.