WeakMap与Map，使用WeakMap实现深拷贝循环引用问题

  function deepClone (origin, weakMap = new WeakMap()) {
    if (origin == undefined || typeof origin != ‘object‘) {
      return origin
    }
    if (origin instanceof Date) {
      return new Date(origin)
    }
    if (origin instanceof RegExp) {
      return new RegExp(origin)
    }
    const val = weakMap.get(origin)
    if (val) return val
    const target = new origin.constructor()
    weakMap.set(origin, target)
    for (let k in origin) {
      target[k] = deepClone(origin[k], weakMap)
    }
    return target
  }
测试代码：

let obj1 = {}
obj1.obj2 = obj1
let obj2 = deepClone(obj1)
console.log(obj2, ‘obj2‘)