Added error messages

src/javascript/index.js

@@ -32,7 +32,11 @@ setEventListeners(upload, async () => {
             method: 'POST',
             body: formData
         }).then((response) => {
-            location.reload();
+            if (!response.ok) {
+                alert(`Upload unsuccessful. ${response.status}`);
+            } else {
+                location.reload();
+            }
         });
     }
     const onSelectFile = () => upload(input.files[0]);