class ChatServer {
  constructor() {
    this.clients = new Set();
    this.messageLog = [];
  }
  
  connect(client) {
    this.clients.add(client);
    return () => this.clients.delete(client);
  }
  
  broadcast(message, sender) {
    this.messageLog.push(message);
    this.clients.forEach(client => {
      if (client !== sender) {
        client.receive(message);
      }
    });
  }
}

const server = new ChatServer();
const david = { name: 'David', receive: msg => console.log(`David got: ${msg}`) };
const sarah = { name: 'Sarah', receive: msg => console.log(`Sarah got: ${msg}`) };
const emma = { name: 'Emma', receive: msg => console.log(`Emma got: ${msg}`) };

const disconnectDavid = server.connect(david);
server.connect(sarah);
server.connect(emma);
server.broadcast('Hello everyone!', david);
disconnectDavid();
server.broadcast('Is David still here?', sarah);

console.log(server.clients.size);