TypeScript实现DeepClone函数

function deepClone<T>(obj: T, hashMap = new WeakMap()): T {
  if (typeof obj !== 'object' || obj === null) {
    return obj
  }

  const type = Object.prototype.toString.call(obj)

  // 特殊类型处理
  if (type === '[object Date]') {
    return new Date((obj as Date).getTime()) as T
  }

  if (type === '[object RegExp]') {
    const reg = new RegExp((obj as RegExp).source, (obj as RegExp).flags)
    reg.lastIndex = (obj as RegExp).lastIndex
    return reg as T
  }

  if (type === '[object Error]') {
    const error = new Error((obj as Error).message)
    error.stack = (obj as Error).stack
    return error as T
  }

  if (hashMap.has(obj)) {
    return hashMap.get(obj) as T
  }

  const copy: any = Array.isArray(obj) ? [] : {}

  hashMap.set(obj, copy)

  Object.keys(obj).forEach((key) => {
    if (Object.prototype.hasOwnProperty.call(obj, key)) {
      // 属性值为 undefined 或 NaN，需要特殊处理
      const value = obj[key]
      copy[key] =
        value === undefined
          ? undefined
          : value !== value
          ? NaN
          : deepClone(value, hashMap)
    }
  })

  return copy as T
}