add saving draft to localStorage

data/static/js/bits/progressive-enhancement.js

@@ -3,6 +3,10 @@ export const b = {
 }
 
 export function enhance(_, __, el) {
+  if (el === undefined) { // nothing to enhance but init still runs
+    return;
+  }
+
   if (el.classList.contains('js-only')) {
     el.classList.remove('js-only');
   }