Step 3: To notify clients when a new chat message is sent, use a WebSocket, which allows for bidirectional communication between clients and a server. Download a package called socket.io. To use the package in your code, go to index.js, and add the following near the top:

let socketio = require(`socket.io`)

At the bottom, replace app.listen with:

let server = app.listen(3000)
let io = new socketio.Server(server)

The io object can be used to broadcast data to all clients. To broadcast a new chat message, add the following at the start of your endpoint for posting chat messages:

io.emit(`message`, request.body.message)

You will have clients listen for broadcasted chat messages in the next step.