diff --git a/8.countingSort.md b/8.countingSort.md
index d0930cf..75ffd0a 100644
--- a/8.countingSort.md
+++ b/8.countingSort.md
@@ -10,7 +10,8 @@
 ## 2. JavaScript 代码实现
 
 ```js
-function countingSort(arr, maxValue) {
+function countingSort(arr) {
+    var maxValue = Math.max(...arr);
     var bucket = new Array(maxValue+1),
         sortedIndex = 0;
         arrLen = arr.length,
@@ -158,4 +159,4 @@ function countingSort($arr, $maxValue = null)
 
     return $arr;
 }
-```
\ No newline at end of file
+```