JS数组递归循环

<script>
        var arr = [1,2,3,[1,2,3,1,3,[1,2,3,6,4,[1,2,3,1]]],2]; 

        let last = []
        function multiarr(arr){
          let k=0
          for (let i=0;i<arr.length;i++){
            if(arr[i] instanceof Array){
              k++
              arr = arr[i];
              multiarr(arr);
            }
          }
          if(k==0){
            last = arr
          }
          return last
        }
        console.log(multiarr(arr));
</script>