JavaScript 深拷贝(无 function 拷贝)

function isObject (obj) {
  return (typeof obj === 'object' || typeof obj === 'function') 
          && (obj !== null)
}

function deepcopy (obj, hash = new WeakMap()) {
  let copyObj, 
      constructor = obj.constructor
  switch (constructor) {
    case RegExp:
    case Date:
      copyObj = new constructor(obj)
      break;
    default:
      if (hash.has(obj)) return hash.get(obj)
      copyObj = Array.isArray(obj) ? [] : {}
      hash.set(obj, copyObj)
  }
  for (let key in obj) {
    copyObj[key] = isObject(obj[key]) ? deepcopy((obj[key]), hash) : obj[key]
  }
  return copyObj
}

var obj = {
  arr: [1, 2],
  obj: { key: {prop: 'something'} },
  a: () => { },
  date: new Date(),
  regExp: new RegExp('-', "g"),
  reg: /-/g,
  null: null,
  undefined: undefined
}
obj.self = obj
var result = deepcopy(obj)
console.log(result)