diff --git a/hello/app.js b/hello/app.js
index 5dd518b..d1d62cd 100644
--- a/hello/app.js
+++ b/hello/app.js
@@ -1 +1,10 @@
-console.log("Hello!")
+"use strict;"
+
+let bookId = 0;
+
+function genNewBookId() {
+    bookId++;
+    return bookId;
+}
+
+console.log(genNewBookId());