Design Pattern - Observable

design-pattern-observable.js

class Stock {
  constructor(symbol) {
    this.symbol = symbol;
    this.price = 0;
    this.observers = [];
  }

  // Subscribe to stock price changes
  subscribe(observer) {
    this.observers.push(observer);
    return () => this.unsubscribe(observer);
  }

  // Unsubscribe from stock price updates
  unsubscribe(observer) {
    this.observers = this.observers.filter((obj) => obj !== observer);
    console.log(`${observer.name} has been unsubscribed successfully`);
  }

  // Notify all observers when price changes
  notify() {
    this.observers.forEach((observer) => observer.update(this));
  }

  // Simulate a price change
  changePrice(newPrice) {
    this.price = newPrice;
    this.notify(); // Notify all observers
  }
}

class Investor {
  constructor(name) {
    this.name = name;
  }

 // Update method called when stock price changes
  update(stock) {
    console.log(
     `${this.name} has been notified: ${stock.symbol} is now at ₹${stock.price}`
    );
  }
}

// Usage Example
const sbiStock = new Stock("SBI");
const investor1 = new Investor("Yuvraj");
const investor2 = new Investor("Ganesh");

const unsubscribeInvestor1 = sbiStock.subscribe(investor1);
const unsubscribeInvestor2 = sbiStock.subscribe(investor2);

sbiStock.changePrice(1500);
unsubscribeInvestor2(); // Ganesh unsubscribes

// After 2 seconds, stock price is changed
setTimeout(() => {
 sbiStock.changePrice(1600); // Only Yuvraj will be notified
}, 2000);