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Challenge: Solution Review

Challenge: Solution Review

This lesson will explain the solution to the problem from the last coding challenge.

Solution

Node.js
class Auctioneer
{
    constructor(){
        this.bidderList = []
    }
    
    announceNewBidderPrice()
    {
        this.notifyBidders();
    }
     
    registerBidder(bidder)
    {
        this.bidderList.push(bidder);
    }
    
    notifyBidders()
    {
        this.bidderList.forEach(bidder => bidder.update())
    }
}
class Bidder 
{
    constructor(name){
        this.name = name
        this.bidPrice = null
    }
    
    update()
    {
        console.log(`${this.name} is offering ${this.bidPrice} dollars`);
        if (this.bidPrice > 500)
        {
            console.log(`Sold to ${this.name}`);
        }
    }
        
    giveNewPrice(price)
    {
        this.bidPrice = price;
    }
}
auctioner = new Auctioneer();
bidder1 = new Bidder("Ross");
auctioner.registerBidder(bidder1);
bidder2 = new Bidder("Joey");
auctioner.registerBidder(bidder2);
bidder1.giveNewPrice(200);
bidder2.giveNewPrice(350);
auctioner.announceNewBidderPrice()
bidder1.giveNewPrice(400);
bidder2.giveNewPrice(550);
auctioner.announceNewBidderPrice()

Explanation

In this example, we have the subject class Auctioneer that stores the list of all bidders to whom it announces the bidding prices.

class Auctioneer
{
    constructor(){
        this.bidderList = []
    }
    //code...
}

The constructor initializes the list bidderList that stores all the bidders participating in the auction.

It also defines the registerBidder function that registers a bidder for the auction.

registerBidder(bidder)
{
        this.bidderList.push(bidder);
}

It also has the announceNewBidderPrice function:

announceNewBidderPrice()
{
   this.notifyBidders();
}

When a bidder gives a price for the object being auctioned, the auctioneer invokes announceNewBidderPrice function to notify all the bidders about the price. How are the bidders notified? Using the notifyBidders function.

notifyBidders()
{
   this.bidderList.forEach(bidder => bidder.update())
}

This function sends an announcement regarding the price given by each bidder in the list. It does so by calling the update function. We’ll take a look at it when we discuss the Bidder class.

Here’s what the Bidder class looks like:

class Bidder 
{
  constructor(name){
     this.name = name
     this.bidPrice = null
   }
   //code... 
}

The constructor initializes the properties name and bidPrice for a bidder.

The bidPrice is set using the giveNewPrice function:

giveNewPrice(price)
{
   this.bidPrice = price;
}

The Bidder also has the update function.

update(){
   console.log(`＄{this.name} is offering ＄{this.bidPrice} dollars`);
    if (this.bidPrice > 500){
            console.log(`Sold to ＄{this.name}`);
  }
}

This function is invoked by the Auctioneer to notify the bidders about the new price given by a bidder. Hence, it displays a message announcing the name of the bidder and bidPrice offered by them. It also checks if the bidder’s price is greater than 500; if so, the object is sold to that bidder, and an announcement of the winner is made.

Let’s discuss the visitor pattern in the next lesson.