chatroom.js

// each participant represented by Participant object
class Participant {
 constructor(name) {
   this.name = name;
 }
  getParticiantDetails() {
   return this.name;
 }
}
 
// Mediator
class Chatroom {
 constructor() {
   this.participants = {};
 }
 
 register(participant) {
   this.participants[participant.name] = participant;
   participant.chatroom = this;
 }
 
 send(message, from, to) {
   if (to) {
     // single message
     to.receive(message, from);
   } else {
     // broadcast message to everyone
     for (key in this.participants) {
       if (this.participants[key] !== from) {
         this.participants[key].receive(message, from);
       }
     }
   }
 }
}
 
// usage
// Create two participants  
 const john = new Participant('John');
 const snow = new Participant('Snow');
// Register the participants to Chatroom
 var chatroom = new Chatroom();
 chatroom.register(john);
 chatroom.register(snow);
// Participants now chat with each other
 john.send('Hey, Snow!');
 john.send('Are you there?');
 snow.send('Hey man', yoko);
 snow.send('Yes, I heard that!');

Looks like this was adapted from this -> dofactory design patterns - mediator

I fixed the errors if anywhere cares to check it out -> https://glitch.com/edit/#!/javascript-mediator-pattern