class CustomWeakMap {

  constructor(relationKey = '__relation') {

    this.relationKey = relationKey;

  }

​

  // 设置键值对 - 使用直接属性赋值以提高性能

  set(key, value) {

    key[this.relationKey] = value;

    return this;

  }

​

  // 获取键对应的值

  get(key) {

    return key[this.relationKey];

  }

​

  // 检查键是否存在

  has(key) {

    return this.relationKey in key;

  }

​

  // 删除键值对

  delete(key) {

    return delete key[this.relationKey];

  }

}

var to0 = {};

var to1 = {};

var to2 = {}

var wm = new WeakMap();

var sy = Symbol();

var cy = new CustomWeakMap();

wm.set(to1, 1);

to1[sy] = 1;

cy.set(to2,1)