diff --git a/public/error.js b/public/error.js
index f6c38b9..412fde6 100644
--- a/public/error.js
+++ b/public/error.js
@@ -1,3 +1,4 @@
+"use strict";
 const error = document.getElementById("error");
 const errorCode = document.getElementById("error-code");
 const registerButton = document.getElementById("register-sw");
diff --git a/public/index.js b/public/index.js
index 7b6db8f..35804cb 100644
--- a/public/index.js
+++ b/public/index.js
@@ -1,3 +1,4 @@
+"use strict";
 const form = document.getElementById("uv-form");
 const input = document.getElementById("uv-address");
 const error = document.getElementById("error");
diff --git a/public/register-sw.js b/public/register-sw.js
index 6b92f04..cb8fe7e 100644
--- a/public/register-sw.js
+++ b/public/register-sw.js
@@ -1,3 +1,4 @@
+"use strict";
 /**
  * Global util
  * Used in 404.html and index.html