How does the observer pattern work?

Can you explain how the observer pattern works in programming?

Sure! The observer pattern is a design pattern where an object, called the subject, maintains a list of dependents, called observers, and notifies them of state changes.

What are some real-world examples of the observer pattern?

Common examples include event handling in GUI applications, where UI components listen for events, and stock market applications where investors are notified of price changes.

How is it different from the publisher-subscriber pattern?

The observer pattern is a specific implementation of the publisher-subscriber pattern, where the subject directly maintains a list of observers, while in the publisher-subscriber pattern, the communication can be more decoupled.

Can you show me a code example of the observer pattern?

Certainly! Here's a simple JavaScript example:

class Subject {
    constructor() {
        this.observers = [];
    }
    addObserver(observer) {
        this.observers.push(observer);
    }
    notifyObservers(data) {
        this.observers.forEach(observer => observer.update(data));
    }
}

class Observer {
    update(data) {
        console.log(`Observer received data: ${data}`);
    }
}

const subject = new Subject();
const observer1 = new Observer();
subject.addObserver(observer1);
subject.notifyObservers('Hello Observers!');

This code demonstrates how a subject notifies its observers.