How do I implement the Observer pattern in JavaScript?

How do I implement the Observer pattern in JavaScript?

The Observer pattern is a design pattern that allows an object, known as the subject, to maintain a list of its dependents, called observers, and notify them of any state changes. Would you like a code example?

Yes, please provide a code example.

Sure! Here's a simple implementation:

class Subject {
    constructor() {
        this.observers = [];
    }

    addObserver(observer) {
        this.observers.push(observer);
    }

    removeObserver(observer) {
        this.observers = this.observers.filter(obs => obs !== observer);
    }

    notifyObservers(data) {
        this.observers.forEach(observer => observer.update(data));
    }
}

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

// Usage
const subject = new Subject();
const observer1 = new Observer();
const observer2 = new Observer();

subject.addObserver(observer1);
subject.addObserver(observer2);
subject.notifyObservers('Hello Observers!');

This code defines a Subject that can add and remove observers and notify them of changes.

How can I test this implementation?

You can test it by creating instances of the Subject and Observer classes, adding observers to the subject, and calling notifyObservers with different data. This will trigger the update method in each observer.