深拷贝

let arr = [1,2,3,4];

      function deepClone(obj) {

      //定义对象来判断当前的参数是数组还是对象

      let objClone = Array.isArray(obj) ? [] : {};

      //如果obj存在并且为对象    

      if(obj && typeof obj == "object") {

        for(let key in obj) {

          if(obj.hasOwnProperty(key)) {

            //如果obj的子元素为对象，那么递归（层级遍历）

            if(obj[key] && typeof obj[key] == "object") {

              objClone[key] = deepClone(obj[key]);

            } else {

              //如果不是，直接赋值

                objClone[key] = obj[key];

              }

            }

          }

        }

        return objClone;

      }

      let arr1 = deepClone(arr);

      console.log(arr1);//[ [1, 2, 3, 4]]

      arr1[2] = 5;

      console.log(arr1);//[1, 2, 5, 4]

      console.log(arr);//[1, 2, 3, 4]