fetch items from server before locally checking available IDs

static/form.js

@@ -3,12 +3,16 @@ const id = new URLSearchParams(window.location.search).get('id');
 
 document.onreadystatechange = function() {
   if (document.readyState === 'interactive') {
+    fetchItems(fillForm);
+  }
+}
+
+function fetchItems(cb) {
   fetch('/api/items').then(r => r.json()).then((data) => {
     items = data;
-      fillForm();
+    cb();
   });
 }
-}
 
 function fillForm() {
   const item = items[id];
@@ -77,6 +81,7 @@ function save() {
     hidden: document.getElementById('hidden').checked,
   }
 
+  fetchItems(() => {
     if (item.id.includes('?')) {
       let n = 1;
       while (true) {
@@ -111,6 +116,7 @@ function save() {
     }).catch(error => {
       alert(`Error:\n${error}`);
     });
+  });
 }
 
 function del() {