单例模式JavaScript具体实现

立即执行函数

const Singleton = (function () {
    let instance;

    function createInstance() {
        let object = new Object("I am the instance");
        return object;
    }

    return {
        getInstance: function () {
            if (!instance) {
                instance = createInstance();
            }
            return instance;
        }
    };
})();

const instance1 = Singleton.getInstance();
const instance2 = Singleton.getInstance();

console.log(instance1 === instance2); // true

ES6 Class

class Singleton {
    constructor() {
        if (!Singleton.instance) {
            Singleton.instance = this;
        }
        return Singleton.instance;
    }
}

const instance1 = new Singleton();
const instance2 = new Singleton();

console.log(instance1 === instance2); // true

Proxy方式

【经典面试题】ES6中的proxy和Reflect

class Person {
  constructor() {
    this.name = "tom"
  }
}


const Singleton = new Proxy(Person, {
  // construct
  // https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Proxy/Proxy/construct
  construct(target, args) {
    // target 是 Person 类
    // args 是代理的参数

    // console.log(`Creating a ${target.name}`);
    // Expected output: "Creating a Person"

    if (target.instance == undefined) {
        target.instance = new target(...args);
    }
    return target.instance;
  }
})


const instance1 = new Singleton();
const instance2 = new Singleton();
console.log(instance1 === instance2); // true
console.log(instance1.name); // tom
console.log(instance2.name); // tom