Observer & Singleton Patterns

Which code demonstrates a correct implementation of the Observer Pattern?

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

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

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

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

class Observer {
  update(data) {
    console.log('Received update:', data);
  }
}

The Subject class shouldn't store observers
The Observer class should have an addObserver method
The implementation follows the standard Observer Pattern structure
This code demonstrates a correct implementation of the Observer Pattern where: 1) The Subject maintains a list of observers, 2) Provides methods to add/remove observers, 3) Notifies all observers of changes, and 4) Observers implement an update method to receive notifications. This structure allows for loose coupling between the subject and its observers.
The notify method should be in the Observer class

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