JavaScript Design Patterns for Coding Interviews/

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Mediator Pattern

Mediator Pattern

This lesson explains the mediator pattern in detail with the aid of a coding example.

We'll cover the following...

What is the mediator pattern?

It is a behavioral pattern that allows a mediator (a central authority) to act as the coordinator between different objects, instead of the objects referring to each other directly. A mediator as the name implies, is a central authority through which various components can communicate. It allows the loose coupling of objects.

A real-life example is a chat application. Here, the chat box acts as the mediator through which various users interact with one another.

Example

Now, let’s implement the mediator pattern for the chat room example discussed above.

Node.js
class User{
  constructor(name,userId){
    this.name = name
    this.userId = userId
    this.chatbox = null;
  }
  sendMessage(message,sendTo){
    this.chatbox.send(message,this,sendTo)
  }
  receiveMessage(message,receiveFrom){
    console.log(`${receiveFrom.name} sent the message: ${message}`)
  }
}
class ChatBox{
  
  constructor(){
    this.users = []
  }
  
  register(user){
    this.users[user.userId] = user
    user.chatbox = this;
  }
  send(message,receiveFrom,sendTo){
      sendTo.receiveMessage(message, receiveFrom);    
  }
}
var chatbox = new ChatBox();
var joey = new User("Joey",1);
var phoebe = new User("Phoebe",2);
chatbox.register(joey);
chatbox.register(phoebe);
joey.sendMessage("Hey, how you doing?",phoebe);
phoebe.sendMessage("Smelly Cat, Smelly Cat..",joey);
joey.sendMessage("I love this song!", phoebe);

Explanation

The code above implements a chat box. Different users access the chat box to interact with each other. Let’s start by discussing the User class ...