add error for non-whitelisted http: locations

public/register-sw.js

@@ -4,11 +4,22 @@
  */
 const stockSW = "/uv/sw.js";
 
+/**
+ * List of hostnames that are allowed to run serviceworkers on http:
+ */
+const swAllowedHostnames = ["localhost", "127.0.0.1"];
+
 /**
  * Global util
  * Used in 404.html and index.html
  */
 async function registerSW() {
+  if (
+    location.protocol !== "https:" &&
+    !swAllowedHostnames.includes(location.hostname)
+  )
+    throw new Error("Service workers cannot be registered without https.");
+
   if (!navigator.serviceWorker)
     throw new Error("Your browser doesn't support service workers.");