Observer pattern using ts

Observer.ts

interface Subject {
    registerObserver(o: Observer): void;
    removeObserver(o: Observer): void;
    notifyObservers(): void;
}

interface Observer {
    update(temperature: number): void;
}

class WeatherStation implements Subject {
    private temperature: number;
    private observers: Observer[] = [];
    
    setTemperature(temp: number){
        console.log(`WeatherStation: new temperature measurement ` + temp);
        this.temperature = temp;
        this.notifyObservers();
    }
    
    public registerObserver(o: Observer) {
        this.observers.push(o);
    }
    public removeObserver(o: Observer) {
        let index = this.observers.indexOf(o);
        this.observers.splice(index, 1);
    }
    public notifyObservers() {
        for (let observer of this.observers) {
            observer.update(this.temperature);
        }
    }
}

class TemperatureDisplay implements Observer {
    
    private subject: Subject;
    constructor(weatherStation: Subject) {
        this.subject = weatherStation;
        weatherStation.registerObserver(this);
    }
    
    public update(temperature: number) {
        console.log(`Temperature display, i need to update my display`);
    }
}

class Fan implements Observer {
    
    private subject: Subject;
    constructor(weatherStation: Subject) {
        this.subject = weatherStation;
        weatherStation.registerObserver(this);
    }
    
    public update(temperature: number) {
        if (temperature > 25) {
            console.log(`I am fan and i need to enable`);
        } else {
            console.log(`I am fan and i need to disable`)
        }
    }
}

let weatherStation = new WeatherStation();
let tempDisplay = new TemperatureDisplay(weatherStation);
let fan = new Fan(weatherStation);

weatherStation.setTemperature(20);
weatherStation.setTemperature(30);