JavaScript单例模式详解与实例保障

const Singleton = (function() {
  let instance = null;
  function createInstance() {
    return {
      data: Math.random(),
      getName() { return 'Singleton'; }
    };
  }
  return {
    getInstance() {
      if (!instance) {
        instance = createInstance();
      }
      return instance;
    }
  };
})();

// 使用
const a = Singleton.getInstance();
const b = Singleton.getInstance();
console.log(a === b); // true

class Logger {
  #logHistory = [];
  static #instance = null;

  constructor() {
    if (Logger.#instance) {
      return Logger.#instance;
    }
    Logger.#instance = this;
  }

  static getInstance() {
    if (!Logger.#instance) {
      Logger.#instance = new Logger();
    }
    return Logger.#instance;
  }

  log(msg) {
    this.#logHistory.push(msg);
  }
}

const l1 = Logger.getInstance();
const l2 = Logger.getInstance();
console.log(l1 === l2); // true

class Logger {
  constructor() {
    this.logs = [];
  }
  log(msg) {
    this.logs.push(`[${Date.now()}] ${msg}`);
  }
}

// ✅ 直接导出唯一实例
export default new Logger();

import logger from './logger.js';
import logger2 from './logger.js';
console.log(logger === logger2); // true