diff --git a/hello/app.js b/hello/app.js
index 7d9c1f2..7fe3c0a 100644
--- a/hello/app.js
+++ b/hello/app.js
@@ -1,9 +1,9 @@
-
+"use strict;"
 
 let bookId = 0;
 
 function genNewBookId() {
-    bookID = 1
+    bookID = 1;
     bookID++;
     return bookId;
 }