diff --git a/background.html b/background.html
index 9255fdd79..a65bbc589 100644
--- a/background.html
+++ b/background.html
@@ -35,7 +35,6 @@
     <script type="text/javascript" src="js/storage.js"></script>
     <script type="text/javascript" src="js/libtextsecure.js"></script>
 
-    <script type="text/javascript" src="js/focus_listener.js"></script>
     <script type="text/javascript" src="js/notifications.js"></script>
     <script type="text/javascript" src="js/read_receipts.js"></script>
     <script type="text/javascript" src="js/read_syncs.js"></script>
diff --git a/js/focus_listener.js b/js/focus_listener.js
deleted file mode 100644
index c9a728233..000000000
--- a/js/focus_listener.js
+++ /dev/null
@@ -1,14 +0,0 @@
-// eslint-disable-next-line func-names
-(function() {
-  'use strict';
-
-  let windowFocused = false;
-  window.addEventListener('blur', () => {
-    windowFocused = false;
-  });
-  window.addEventListener('focus', () => {
-    windowFocused = true;
-  });
-
-  window.isFocused = () => windowFocused;
-})();
diff --git a/ts/util/focusListener.ts b/ts/util/focusListener.ts
new file mode 100644
index 000000000..2fb81cf2c
--- /dev/null
+++ b/ts/util/focusListener.ts
@@ -0,0 +1,9 @@
+let windowFocused = false;
+window.addEventListener('blur', () => {
+  windowFocused = false;
+});
+window.addEventListener('focus', () => {
+  windowFocused = true;
+});
+
+export const isWindowFocused = () => windowFocused;