Add a early js script.

assets/js/script-early.js

@@ -0,0 +1,13 @@
+/**
+ * @file
+ * A JavaScript file for the theme. Runs first, before jQuery etc. have loaded.
+ */
+
+(function () {
+
+  'use strict';
+
+  // Add a js class to the html-tag when JavsScript is active.
+  document.querySelector('html').classList.replace('nojs', 'js');
+
+})();