JS单例（ES6）

ES6引入class和constructor来创建对象，下面我们使用ES6实现单例模式
使用static关键字定义静态方法

class Singleton {
    constructor(name) {
        this.name = name;
        this.instance = null;
    }

    static getInstance(name) {
        if(!this.instance) {
            this.instance = new Singleton(name);
        }
        return this.instance;
    }
}

const singleton1 = Singleton.getInstance('singleton1');
const singleton2 = Singleton.getInstance('singleton2');
console.log(singleton1 === singleton2); //true

JS中没有私有变量，所以我们借助Symbol

const name1 = Symbol('name1');
class Singleton {
    constructor(name) {
        this.name = name;
        this[name1] = name;
        this.instance = null;
    }

    static getInstance(name) {
        if(!this.instance) {
            this.instance = new Singleton(name);
        }
        return this.instance;
    }
}

const singleton1 = Singleton.getInstance('singleton1');
console.log(singleton1.name); //singleton1
console.log(singleton1.name1); //undefined