diff --git a/static/skin/viewer.js b/static/skin/viewer.js
index 085777aab..750cddf61 100644
--- a/static/skin/viewer.js
+++ b/static/skin/viewer.js
@@ -35,13 +35,15 @@ let currentBookTitle = null;
 
 const bookUIGroup = document.getElementById('kiwix_serve_taskbar_book_ui_group');
 const homeButton = document.getElementById('kiwix_serve_taskbar_home_button');
+const contentIframe = document.getElementById('content_iframe');
+
 
 function gotoMainPageOfCurrentBook() {
   location.hash = currentBook + '/';
 }
 
 function gotoUrl(url) {
-  cf.src = url;
+  contentIframe.src = url;
 }
 
 function gotoRandomPage() {
@@ -110,27 +112,26 @@ function iframeUrl2UserUrl(url, query) {
   return url.split('/').slice(2).join('/');
 }
 
-const cf = document.getElementById('content_iframe');
-
 function handle_visual_viewport_change() {
-  cf.height = window.visualViewport.height - cf.offsetTop - 4;
+  contentIframe.height = window.visualViewport.height - contentIframe.offsetTop - 4;
 }
 
 function handle_location_hash_change() {
   const hash = window.location.hash.slice(1);
+  console.log("handle_location_hash_change: " + hash);
   updateCurrentBookIfNeeded(hash);
   const iframeContentUrl = userUrl2IframeUrl(hash);
-  console.log("handle_location_hash_change: " + hash);
-  if ( iframeContentUrl != cf.contentWindow.location.pathname ) {
-    cf.contentWindow.location.replace(iframeContentUrl);
+  if ( iframeContentUrl != contentIframe.contentWindow.location.pathname ) {
+    contentIframe.contentWindow.location.replace(iframeContentUrl);
   }
 }
 
 function handle_content_url_change() {
-  document.title = cf.contentDocument.title;
-  const iframeContentUrl = cf.contentWindow.location.pathname;
-  const iframeContentQuery = cf.contentWindow.location.search;
-  console.log('handle_content_url_change: ' + cf.contentWindow.location.href);
+  const iframeLocation = contentIframe.contentWindow.location;
+  console.log('handle_content_url_change: ' + iframeLocation.href);
+  document.title = contentIframe.contentDocument.title;
+  const iframeContentUrl = iframeLocation.pathname;
+  const iframeContentQuery = iframeLocation.search;
   const newHash = '#' + iframeUrl2UserUrl(iframeContentUrl, iframeContentQuery);
   const viewerURL = location.origin + location.pathname + location.search;
   window.location.replace(viewerURL + newHash);
diff --git a/test/server.cpp b/test/server.cpp
index feca68b2e..57a2158ac 100644
--- a/test/server.cpp
+++ b/test/server.cpp
@@ -202,7 +202,7 @@ R"EXPECTEDRESULT(                                <img src="../skin/download.png?
       /* url */ "/ROOT/viewer",
 R"EXPECTEDRESULT(    <link type="text/css" href="./skin/taskbar.css?cacheid=26082885" rel="Stylesheet" />
     <link type="text/css" href="./skin/css/autoComplete.css?cacheid=08951e06" rel="Stylesheet" />
-    <script type="text/javascript" src="./skin/viewer.js?cacheid=b3ef34f2" defer></script>
+    <script type="text/javascript" src="./skin/viewer.js?cacheid=d7d3dac9" defer></script>
     <script type="text/javascript" src="./skin/autoComplete.min.js?cacheid=1191aaaf"></script>
       const blankPageUrl = `${root}/skin/blank.html`;
             <label for="kiwix_button_show_toggle"><img src="./skin/caret.png?cacheid=22b942b4" alt=""></label>