简易版

const getType = obj => Object.prototype.toString.call(obj)
function deepClone(target, map = new WeakMap()) {
  if (typeof target !== 'object') return target
  if (map.get(target)) return target
  let cloneTarget = Array.isArray(target) ? [] : new target.constructor()
  let type = getType(target)
  map.set(target, true)
  if (type === '[object Map]') {
    target.forEach((item, key) => {
      cloneTarget.set(deepClone(key, map), deepClone(item, map))
    })
  }
  if (type === '[object Set]') {
    target.forEach((item) => {
      cloneTarget.add(deepClone(item, map))
    })
  }
  for (const key in target) {
    if (target.hasOwnProperty(key)) {
      cloneTarget[key] = deepClone(target[key], map)
    }
  }
  return cloneTarget
}

for in 会遍历原型链上的属性，hasOwnProperty不会，所以需要用hasOwnProperty判断下

PLUS版本

const getType = obj => Object.prototype.toString.call(obj);
const isObject = (target) => (typeof target === 'object' || typeof target === 'function') && target !== null;
const canTraverse = {
  '[object Map]': true,
  '[object Set]': true,
  '[object Array]': true,
  '[object Object]': true,
  '[object Arguments]': true,
};
const mapTag = '[object Map]';
const setTag = '[object Set]';
const boolTag = '[object Boolean]';
const numberTag = '[object Number]';
const stringTag = '[object String]';
const symbolTag = '[object Symbol]';
const dateTag = '[object Date]';
const errorTag = '[object Error]';
const regexpTag = '[object RegExp]';
const funcTag = '[object Function]';
const handleRegExp = (target) => {
  const { source, flags } = target;
  return new target.constructor(source, flags);
}
const handleFunc = (func) => {
  // 箭头函数直接返回自身
  if(!func.prototype) return func;
  const bodyReg = /(?<={)(.|\n)+(?=})/m;
  const paramReg = /(?<=\().+(?=\)\s+{)/;
  const funcString = func.toString();
  // 分别匹配 函数参数 和 函数体
  const param = paramReg.exec(funcString);
  const body = bodyReg.exec(funcString);
  if(!body) return null;
  if (param) {
    const paramArr = param[0].split(',');
    return new Function(...paramArr, body[0]);
  } else {
    return new Function(body[0]);
  }
}
const handleNotTraverse = (target, tag) => {
  const Ctor = target.constructor;
  switch(tag) {
    case boolTag:
      return new Object(Boolean.prototype.valueOf.call(target));
    case numberTag:
      return new Object(Number.prototype.valueOf.call(target));
    case stringTag:
      return new Object(String.prototype.valueOf.call(target));
    case symbolTag:
      return new Object(Symbol.prototype.valueOf.call(target));
    case errorTag: 
    case dateTag:
      return new Ctor(target);
    case regexpTag:
      return handleRegExp(target);
    case funcTag:
      return handleFunc(target);
    default:
      return new Ctor(target);
  }
}
const deepClone = (target, map = new WeakMap()) => {
  if(!isObject(target)) 
    return target;
  let type = getType(target);
  let cloneTarget;
  if(!canTraverse[type]) {
    // 处理不能遍历的对象
    return handleNotTraverse(target, type);
  }else {
    // 这波操作相当关键，可以保证对象的原型不丢失！
    let ctor = target.constructor;
    cloneTarget = new ctor();
  }
  if(map.get(target)) 
    return target;
  map.set(target, true);
  if(type === mapTag) {
    //处理Map
    target.forEach((item, key) => {
      cloneTarget.set(deepClone(key, map), deepClone(item, map));
    })
  }
  if(type === setTag) {
    //处理Set
    target.forEach(item => {
      cloneTarget.add(deepClone(item, map));
    })
  }
  // 处理数组和对象
  for (let prop in target) {
    if (target.hasOwnProperty(prop)) {
        cloneTarget[prop] = deepClone(target[prop], map);
    }
  }
  return cloneTarget;
}

参考文章

loash
如何写出一个惊艳面试官的深拷贝?