ES6 Proxy实现单例模式如何实现？

Question

const singletonify = fn => {

  const one = new fn()

  return new Proxy(fn, {

    construct(target, argumentsList, newTarget) {

      return one

    }

  })

}

class A () {}

const SingleA = singletonify(A)

const a1 = new SingleA()

const a2 = new SingleA()

const a3 = new SingleA()

a1 === a2; //true, but why?

a2 === a3; //true

以上这段代码如何实现单例模式？为何每次创建的const one = new fn();都相同？

Answer 1

one被闭包引用了 在内存中一直存在construct接口拦截了fn的实例化操作 直接返回one 也就是new A();