server.js

var express = require('express');

var app = express();

var server = app.listen(process.env.PORT || 5000);
app.use(express.static('public'));

console.log("My socket server is running");

var socket = require('socket.io');
var io = socket(server);

io.sockets.on('connection', newConnection);

function newConnection(socket) {
  console.log("new connection: ")
  console.log(socket.id);
  
  
  // Handle user events from sketch.js
  socket.on('mouse', mouseEvent);
  socket.on('clear', clearCanvas);

  function mouseEvent(data) {
    data.id = socket.id;
    socket.broadcast.emit('mouse', data);
  }

  function clearCanvas() {
    socket.broadcast.emit('clear');
  }
}