Observer Pattern example in Typescript

ObserverPattern.ts

interface Observable {
    subscribe(observer: Observer): void;
    unsubscribe(observer: Observer): void;
    notify(): void;
}

interface Observer {
    update(subject: Subject);
}

class Subject implements Observable {
    private observers: Observer[] = [];
    subscribe(observer: Observer) {
        this.observers.push(observer);
    }
    unsubscribe(observer: Observer) {
        this.observers = this.observers.filter((o) => {
            return o !== observer
        })
        console.log('observer detached...' + observer.constructor.name);
    }
    notify() {
        this.observers.forEach((o) => {
            o.update(this);
        })
    }

}

class Score extends Subject {
    
    private score: number;

    public updateScore(score: number)
    {
        this.score = score;
        console.log('got new score.....');
        this.notify();
    }

    public getScore() {
        return this.score;
    }
}


class DisplayScore implements Observer {
    update(subject: Score) {
        console.log('Display score: ' + subject.getScore());
    }

}

class CliScore implements Observer {
    update(subject: Score) {
        console.log('CLI score: ' + subject.getScore());
    }

}

const score = new Score();

const display = new DisplayScore();
const cli = new CliScore();

score.subscribe(display);
score.subscribe(cli);

score.updateScore(4);

score.unsubscribe(cli);

score.updateScore(5);

score.unsubscribe(display);

score.updateScore(6);

/* Output of above code
got new score.....
Display score: 4
CLI score: 4
observer detached...CliScore
got new score.....
Display score: 5
observer detached...DisplayScore
got new score.....
*/