A Socket.IO server will be built to respond to a single event named time. When the event is fired, it will get the server's current time and emit another event named "got time?" providing two arguments, the current time and a counter that specifies how many times a request was made.

1. Create a new file named simple-io-server.js

2. Include the Socket.IO module and initialize a new server:

      const io = require('socket.io')() 

3. Define the URL path where connections will be made:

      io.path('/socket.io') 

4. Use the root or "/" namespace:

      const root = io.of('/') 

5. When a new connection is made, initialize a counter variable to 0. Then, add a new listener to the time event that will increase the counter by one, every time there is a new request, and emit the "got time?" event that will be later defined on the client side:

      root.on('connection', socket => { 
          let counter = 0 
          socket.on('time', () => { 
              const currentTime = new Date().toTimeString() 
              counter += 1 
              socket.emit('got time?', currentTime, counter) 
          }) 
      }) 

6. Listen on port 1337 for new connections:

      io.listen(1337) 

7. Save the file

Next, build a Socket.IO client that will connect to our server:

1. Create a new file named simple-io-client.js
2. Include the Socket.IO client module:

      const io = require('socket.io-client') 

3. Initialize a new Socket.IO client providing the server URL and an options object where we will define the path used in the URL where the connections will be made:

      const clientSocket = io('http://localhost:1337', { 
          path: '/socket.io', 
      }) 

4. Add an event listener to the connect event. Then, when a connection is made, using a for loop, emit the time event 5 times:

      clientSocket.on('connect', () => { 
          for (let i = 1; i <= 5; i++) { 
              clientSocket.emit('time') 
          } 
      }) 

5. Add an event listener to the "got time?" event that will expect to receive two arguments the time and a counter that specifies how many requests were made to the server, then print on the console:

      clientSocket.on('got time?', (time, counter) => { 
          console.log(counter, time) 
      }) 

6. Save the file
7. Open a Terminal and run first the Socket.IO server:

    node simple-io-server.js

8. Open another terminal and run the Socket.IO client:

    node simple-io-client.js