index.js

const { WebSocketServer } = require("ws");

const wss = new WebSocketServer({ port: 3000 });

const maxClients = 2;
let rooms = {};

wss.on('connection', function connection(ws) {
  ws.on('message', function message(data) {
    const obj = JSON.parse(data);
    const type = obj.type;
    const params = obj.params;

    switch (type) {
      case "create":
        create(params);
        break;
      case "join":
        join(params);
        break;
      case "leave":
        leave(params);
        break;
      default:
        console.warn(`Type: ${type} unknown`);
        break;
    }
  });

  function generalInformation(ws) {
    let obj;
    if (ws["room"] !== undefined)
      obj = {
        "type": "info",
        "params": {
          "room": ws["room"],
          "no-clients": rooms[ws["room"]].length,
        }
      }
    else
      obj = {
        "type": "info",
        "params": {
          "room": "no room",
        }
      }
  
    ws.send(JSON.stringify(obj));
  }

  function create(params) {
    const room = genKey(5);
    rooms[room] = [ws];
    ws["room"] = room;

    generalInformation(ws);
  }

  function genKey(length) {
    let result = '';
    const characters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
    for (let i = 0; i < length; i++) {
      result += characters.charAt(Math.floor(Math.random() * characters.length));
    }
    return result;
  }

  function join(params) {
    const room = params.code;
    if (!Object.keys(rooms).includes(room)) {
      console.warn(`Room ${room} does not exist!`);
      return;
    }

    if (rooms[room].length >= maxClients) {
      console.warn(`Room ${room} is full!`);
      return;
    }

    rooms[room].push(ws);
    ws["room"] = room;

    generalInformation(ws);
  }

  function leave(params) {
    const room = ws.room;
    rooms[room] = rooms[room].filter(so => so !== ws);
    ws["room"] = undefined;

    if (rooms[room].length == 0)
      close(room);

    generalInformation(ws);
  }

  function close(room) {
    rooms = rooms.filter(key => key !== room);
  }
});