Try without explicit return

src/api/EpiData.ts

@@ -44,26 +44,16 @@ const ENDPOINT = process.env.EPIDATA_ENDPOINT_URL;
 
 export const fetchOptions: RequestInit = process.env.NODE_ENV === 'development' ? { cache: 'force-cache' } : {};
 
-function processResponse<T>(response: Response): Promise<T> {
-  try {
-    if (response.status == 429) {
-      throw new Error(
-        'Rate limit exceeded for anonymous queries. To remove this limit, register a free API key at https://api.delphi.cmu.edu/epidata/admin/registration_form</p>',
-      );
-    }
-    // eslint-disable-next-line @typescript-eslint/no-unsafe-return
-    return response.json();
-  } catch (error) {
-    throw new Error(`[${response.status}] ${response.text()}`);
-  }
-}
-
 export function fetchImpl<T>(url: URL): Promise<T> {
   const urlGetS = url.toString();
   if (urlGetS.length < 4096) {
     // eslint-disable-next-line @typescript-eslint/no-unsafe-return
     return fetch(url.toString(), fetchOptions).then((d) => {
-      return processResponse(d);
+      try {
+        return d.json();
+      } catch (error) {
+        throw new Error(`[${d.status}] ${d.text()}`);
+      }
     });
   }
   const params = new URLSearchParams(url.searchParams);
@@ -74,7 +64,11 @@ export function fetchImpl<T>(url: URL): Promise<T> {
     method: 'POST',
     body: params,
   }).then((d) => {
-    return processResponse(d);
+    try {
+      return d.json();
+    } catch (error) {
+      throw new Error(`[${d.status}] ${d.text()}`);
+    }
   });
 }
 
@@ -209,7 +203,7 @@ export function loadDataSet(
         .alert(
           `
       <div class="uk-alert uk-alert-error">
-        Failed to fetch API data from <a href="${url.href}">API Link</a>.
+        Failed to fetch API data from <a href="${url.href}">API Link</a>:<br/><i>${error}</i>
       </div>`,
         )
         .then(() => null);