diff --git a/test.js b/test.js
index 942fea9..2303fe2 100644
--- a/test.js
+++ b/test.js
@@ -1,3 +1,7 @@
 function hello_world() {
   alert("Hello world")
 }
+
+this.addEventListener('message', function(event) {
+    document.write(event.data); // NOT OK
+})