A real-time chat application built with Node.js, Express, and Socket.io.
In this app :

• there are different chatrooms
• has a sidebar that displays the current room name and a live list of users currently online.
• users of a room are visible to all the users of that particular room
• when a user joins a room, the other users of that room get notified
• time is visible for all the messages : using moment
• when a user leaves, the rest of the users are notified about it

Used :

• Qs (for parsing URL parameters) -> Query string -> search qs cdn and copy the script and use it in the html file
• momentjs for the timestamps
• expressjs
• html, css
• socket.io

Key Concepts of Socket.io :

• Two-way traffic : when A sends a message, it goes to the server. The server instantly "pushes" that message to B. This happens in milliseconds because the "line" is already open.
• Event-Based : Everything in Socket.io is an Event. You name your events whatever you want:
  --- socket.emit('..', data) — Sending an event.
  --- socket.on('..', ...) — Listening for an event.
  
• Broadcasting & Rooms : Socket.io has built-in "logic" that raw WebSockets don't have:
  --- Broadcasting: Sending a message to everyone except the sender.
  --- Rooms: Dividing users into groups (like your "JavaScript" or "Python" rooms) so messages only go to the right people.