对象浅拷贝和深拷贝

浅拷贝：

let obj = {};
let shadowObj = Object.assgin({}, obj);

深拷贝：

let obj = {};
let deepObj = JSON.parse(JSON.stringify(obj));

扩展链接：

• https://www.zhihu.com/question/23031215
• https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Object/assign