Add eslint and prettier to frontend

And format files

frontend/js/index.ts

@@ -1,4 +1,4 @@
 // import CSS so it gets named with a content hash that busts caches
-import "../css/styles.css";
+import '../css/styles.css';
 
-import "./localTimeController";
+import './localTimeController';

frontend/js/localTimeController.ts

@@ -1,24 +1,30 @@
-function convertTimeElements() {
+function convertTimeElements(): void {
   const timeElements = document.querySelectorAll('time.local-time');
   timeElements.forEach((element) => {
-    const utcString = element.getAttribute("datetime");
-    if (utcString) {
+    const utcString = element.getAttribute('datetime');
+    if (utcString !== null) {
       const utcTime = new Date(utcString);
-      element.textContent = utcTime.toLocaleDateString(window.navigator.language, {
-        year: "numeric",
-        month: "long",
-        day: "numeric",
-      });
+      element.textContent = utcTime.toLocaleDateString(
+        window.navigator.language,
+        {
+          year: 'numeric',
+          month: 'long',
+          day: 'numeric',
+        }
+      );
     } else {
-      console.error("Missing datetime attribute on time.local-time element", element);
+      console.error(
+        'Missing datetime attribute on time.local-time element',
+        element
+      );
     }
   });
 }
 
-document.addEventListener("DOMContentLoaded", function() {
+document.addEventListener('DOMContentLoaded', function () {
   convertTimeElements();
 });
 
-document.body.addEventListener('htmx:afterSwap', function() {
+document.body.addEventListener('htmx:afterSwap', function () {
   convertTimeElements();
 });