Observer.ts

interface Observer {
    update(subject: Subject): void;
}

interface Subject {
    attach(observer: Observer): void;
    detach(observer: Observer): void;
    notify(): void;
}

class Lead {
    constructor(
        public name: string,
        public phone: string
    ) {}
}

class NewLead implements Subject {
    private observers: Observer[] = [];
    public state: Lead;

    attach(observer: Observer): void {
        // @ts-ignore
        if (this.observers.includes(observer)) {
            return;
        }
        this.observers.push(observer)
    }

    detach(observer: Observer): void {
        const observerIndex = this.observers.indexOf(observer)
        if (observerIndex == -1) {
            return;
        }
        this.observers.splice(observerIndex, 1);
    }

    notify(): void {
        for (const observer of this.observers) {
            observer.update(this);
        }
    }
}

class NotificationService implements Observer {
    update(subject: Subject): void {
        console.log('NotificationService получил уведомление');
        console.log(subject)
    }
}

class LeadService implements Observer {
    update(subject: Subject): void {
        console.log('LeadService получил уведомление');
        console.log(subject)
    }
}

const subject = new NewLead()
subject.state = new Lead('Влад', '380955551222')
const s1 = new NotificationService()
const s2 = new LeadService()

subject.attach(s1)
subject.attach(s2)
subject.notify();
subject.detach(s1);
subject.notify();