server.js

"use strict";

const express     = require("express");
const http        = require("http");
const app         = express();
const port        = process.env.PORT || 3000;
const server      = http.createServer(app);
const io          = require("socket.io")(server);
const connections = [];

function findConnection(id){
  return connections.filter(function(c) {return c.id === id;})[0];
}
//start ther server listening
server.listen(port, ()=>{
    console.log("Server listening on port: ", server.address().port);
});
              
//serve static files with express
app.use(express.static("./public"));

//listen for a socket io connection event
io.on("connection", (socket) => {
  
  //new connection, save the socket to them
  connections.push({id: socket.id});
  console.log(`## New connection (${socket.id}). Total: ${connections.length}.`);
  
  //listen for a disconnect event
  socket.once("disconnect", () => {
    //find the connection and remove  from the collection
    let connection = findConnection(socket.id);
    if (connection){
      connections.splice(connections.indexOf(connection), 1);
      if (connection.user){
        socket.broadcast.emit("left", connection.user);
        socket.broadcast.emit("online", connections);
        console.log(`## ${connection.user.name}(${connection.id}) disconnected. Remaining: ${connections.length}.`);
      } else {
        console.log(`## Connection (${connection.id}) (${socket.id}) disconnected. Remaining: ${connections.length}.`);
      }
    }
    socket.disconnect();
  });
  
  //listen for a chat message from a socket and broadcast it
  socket.on("join", (user) => {
    //attach the new user to the connection object
    let connection = findConnection(socket.id);
    connection.user = user;
    //emit welcome message to new user
    socket.emit("welcome", `Hi ${user.name}, welcome to WDI SG2 Chat!`);
    //broadcast their arrival to everyone else
    socket.broadcast.emit("joined", user);
    io.sockets.emit("online", connections);
    
    console.log(`## ${connection.user.name} joined the chat on (${connection.id}).`);
  });
  
  //broadcast chat message to other users
  socket.on("chat", (msg) => {
    let connection = findConnection(socket.id);
    //broadcast to other users
    socket.broadcast.emit("chat", { message: msg, user: connection.user});
    
    console.log(`## ${connection.user.name} said: ${msg}`);
  });
  
});