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JavaScript Design Patterns for Coding Interviews

Challenge: Solution Review

Explore a detailed solution review of the Observer behavioral pattern using an Auctioneer and Bidder example. Learn how bidders receive notifications and how the update method handles bid announcements. Understand this pattern's application in JavaScript to enhance coding interview problem solving.

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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. ...