JavaScript单例与观察者模式详解

const Singleton = (function() {
  let instance;
  function createInstance() {
    return { data: 'I am the only one' };
  }
  return {
    getInstance() {
      if (!instance) {
        instance = createInstance();
      }
      return instance;
    }
  };
})();
// 使用
const a = Singleton.getInstance();
const b = Singleton.getInstance();
console.log(a === b); // true

class Singleton {
  static instance = null;
  constructor() {
    if (Singleton.instance) {
      return Singleton.instance;
    }
    this.id = Math.random();
    Singleton.instance = this;
  }
}

class Subject {
  constructor() {
    this.observers = [];
  }
  attach(observer) {
    if (typeof observer.update === 'function') {
      this.observers.push(observer);
    }
  }
  detach(observer) {
    this.observers = this.observers.filter(obs => obs !== observer);
  }
  notify(data) {
    this.observers.forEach(observer => observer.update(data));
  }
}

const observer1 = {
  update(data) {
    console.log('Observer 1 got:', data);
  }
};
const observer2 = {
  update(data) {
    console.log('Observer 2 got:', data);
  }
};

const subject = new Subject();
subject.attach(observer1);
subject.attach(observer2);
subject.notify('Hello from subject!');