对象深拷贝

    let deepCopy = (obj) => {
        var result = Array.isArray(obj) ? [] : {}
        
        for (var key in obj) {
          if (obj.hasOwnProperty(key)) {
            if (typeof obj[key] === 'object' && obj[key]!==null) {
              result[key] = deepCopy(obj[key])   //递归复制
            } else {
              result[key] = obj[key]
            }
          }
        }
        return result
      }