JavaScript单例模式实现方法详解

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

class Singleton {
  constructor() {
    if (Singleton.instance) {
      throw new Error('Use Singleton.getInstance() instead');
    }
    this.data = 'Singleton instance';
    Singleton.instance = this;
  }
  static getInstance() {
    if (!Singleton.instance) {
      Singleton.instance = new Singleton();
    }
    return Singleton.instance;
  }
}

// singleton.js
export const instance = {
  data: 'Module-based singleton',
  count: 0,
  increment() { this.count++; }
};

// app.js
import { instance as a } from './singleton.js';
import { instance as b } from './singleton.js';
console.log(a === b); // true

const ConfigurableSingleton = (function() {
  let instance = null;
  let config = null;
  return {
    getInstance: function(options = {}) {
      if (!instance) {
        config = { ...options, createdAt: Date.now() };
        instance = { config, doSomething() { return 'done'; } };
      }
      return instance;
    }
  };
})();