深拷贝

需要考虑环形依赖问题

function cloneDeep(value) {
  function clone(target, map) {
    if(target === null) return null;
    if(typeof target === 'object') {
      let cloneTarget = Array.isArray(target) ? [] : {}
      if(map.get(target)) {
        return map.get(target);
      }
      map.set(target, cloneTarget);
      for(let key in target) {
        // 对象类型
        cloneTarget[key] = clone(target[key], map);
      }
      return cloneTarget;
    } else {
      // 基础类型
      return target
    }

  }

  return clone(value, new WeakMap())
}

let obj = {
  a: 1,
  b: {
    c: 2
  },
  d: [{e: '3'}, '4']
}
obj.e = obj

console.log(cloneDeep(obj));

进阶版

function cloneDeep(value) {
  function isObject(value) {
    return value !== null && (typeof value === 'object')
  }
  function isFunction() { return typeof value === 'function' }
  function cloneFunction(value) {
    const clone = value.bind({});
    for(key in value) {
      clone[key] = value[key]
    }
    clone.prototype = Object.create(value.prototype)
    return clone;
  }
  function isRegExp(value) { return value instanceof RegExp }
  function cloneRegExp(value) {
    if(value instanceof RegExp) {
      const reg = new RegExp(value.source, value.flags);
      reg.lastIndex = value.lastIndex;
      return reg;
    }
  }
  function clone(target, map) {
    if(isObject(target)) {
      // 正则
      if(isRegExp(target)) return cloneRegExp(target);
      // 函数
      if(isFunction(target)) return cloneFunction(target);
      let cloneTarget = Array.isArray(target) ? [] : {}
      if(map.get(target)) {
        return map.get(target);
      }
      map.set(target, cloneTarget);
      for(let key in target) {
        // 对象类型
        cloneTarget[key] = clone(target[key], map);
      }
      return cloneTarget;
    } else {
      // 基础类型
      return target
    }

  }
  return clone(value, new WeakMap())
}

let obj = {
  a: 1,
  b: {
    c: 2
  },
  d: [{e: '3'}, '4']
}
obj.e = obj

// console.log(cloneDeep(obj), cloneDeep.toString());

// const originalRegExp = /hello\d/ig;
// console.log(isRegExp(originalRegExp)); // true
// console.log(originalRegExp.source); // hello\d
// console.log(originalRegExp.flags); // ig

const source = cloneDeep.toString();
const fn = new Function(source)
console.log(fn(obj))