深度拷贝~~~

      // source是什么类型
      // target就传入相同类型
      const obj = {
        name: 'jack',
        age: 18,
        hobbies: ['唱', '跳', 'rap']
      }
      const arr = [2, [23]]

      function deepCopy(source, target) {
        for (let k in source) {
          let item = source[k]
          if (item instanceof Array) {
            target[k] = []
            deepCopy(item, target[k])
          } else if (item instanceof Object) {
            target[k] = {}
            deepCopy(item, target[k])
          } else {
            target[k] = item
          }
        }
      }

      let o = {}
      let a = []

      // deepCopy(obj, o)
      deepCopy(arr, a)
      console.log(a)