diff --git a/5.mergeSort.md b/5.mergeSort.md
index c030d8f..38c43b1 100644
--- a/5.mergeSort.md
+++ b/5.mergeSort.md
@@ -50,7 +50,7 @@ function mergeSort(arr) {  // 采用自上而下的递归方法
     return merge(mergeSort(left), mergeSort(right));
 }
 
-function merge(left, right)
+function merge(left = [], right = [])
 {
     var result = [];