Observer Design Pattern

// Subject (Observable)

class WeatherStation {

constructor() {

this.temperature = 0;

this.observers = [];

}

addObserver(observer) {

this.observers.push(observer);

}

removeObserver(observer) {

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

}

setTemperature(temperature) {

this.temperature = temperature;

this.notifyObservers();

}

notifyObservers() {

this.observers.forEach(observer => {

observer.update(this.temperature);

});

}

}

// Observer

class Observer {

update(temperature) {}

}

// Concrete Observer

class TemperatureDisplay extends Observer {

update(temperature) {

console.log(`Temperature updated: ${temperature}°C`);

}

}

// Usage

const weatherStation = new WeatherStation();

const temperatureDisplay = new TemperatureDisplay();

weatherStation.addObserver(temperatureDisplay);

weatherStation.setTemperature(25); // Output: Temperature updated: 25°C

weatherStation.setTemperature(30); // Output: Temperature updated: 30°C