Show exterior cells edited in ModList

Also abstracts jsonFetcher and csvFetcher into common lib functions.

lib/api.ts

@@ -0,0 +1,34 @@
+export async function jsonFetcher<T>(url: string): Promise<T | null> {
+  const res = await fetch(url);
+
+  if (!res.ok) {
+    if (res.status === 404) {
+      return null;
+    }
+    const error = new Error("An error occurred while fetching the data.");
+    throw error;
+  }
+
+  return res.json();
+};
+
+export async function jsonFetcherWithLastModified<T>(url: string): Promise<{ data: T, lastModified: string | null } | null> {
+  const res = await fetch(url);
+
+  if (!res.ok) {
+    if (res.status === 404) {
+      return null;
+    }
+    const error = new Error("An error occurred while fetching the data.");
+    throw error;
+  }
+
+  return {
+    lastModified: res.headers.get("Last-Modified"),
+    data: await res.json(),
+  };
+}
+
+export async function csvFetcher(url: string): Promise<string> {
+  return (await fetch(url)).text();
+}