diff --git a/webmusic.js b/webmusic.js
index 0507a4d..e290c80 100644
--- a/webmusic.js
+++ b/webmusic.js
@@ -1,3 +1,5 @@
+'use strict';
+
 let audioPlayer  = new Audio();
 let selectedItem = 0;
 let playingItem  = 0;