Improved logic to check whether more older posts are available

src/routes/+page.svelte

@@ -13,22 +13,44 @@ let interval: NodeJS.Timer | null = null;
 let moreOlderPostsAvailable = true;
 let loadingOlderPosts = false;
 
-function refresh() {
+interface FetchOptions {
+  since?: string,
+  before?: string,
+  count?: number
+}
+
+async function fetchPosts(options: FetchOptions): Promise<Post[]> {
   const params = new URLSearchParams();
-  if (data.posts.length > 0) {
-    params.set('since', data.posts[0].created_at);
+  if (options?.since !== undefined) {
+    params.set('since', options.since);
   }
-  fetch(`/api/posts?${params}`)
-  .then(r => r.json())
-  .then((resp: Post[]) => {
+  if (options?.before !== undefined) {
+    params.set('before', options.before);
+  }
+  if (options?.count !== undefined) {
+    params.set('count', options.count.toFixed(0));
+  }
+
+  const response = await fetch(`/api/posts?${params}`);
+  return await response.json();
+}
+
+function filterDuplicates(posts: Post[]): Post[] {
+  return posts.filter((obj, index, arr) => {
+    return arr.map(mapObj => mapObj.url).indexOf(obj.url) === index;
+  });
+}
+
+function refresh() {
+  let filter: FetchOptions = {};
+  if (data.posts.length > 0) {
+    filter = { since: data.posts[0].created_at };
+  }
+  fetchPosts(filter).then(resp => {
     if (resp.length > 0) {
       // Prepend new posts, filter dupes
       // There shouldn't be any duplicates, but better be safe than sorry
-      const combined = resp.concat(data.posts);
-      const filteredPosts = combined.filter((obj, index, arr) => {
-        return arr.map(mapObj => mapObj.url).indexOf(obj.url) === index;
-      });
-      data.posts = filteredPosts;
+      data.posts = filterDuplicates(resp.concat(data.posts));
     }
   })
   .catch(e => {
@@ -57,24 +79,21 @@ onMount(async () => {
   }
 });
 
-async function loadOlderPosts() {
+function loadOlderPosts() {
   loadingOlderPosts = true;
-  const params = new URLSearchParams();
+  const filter: FetchOptions = { count: 20 };
   if (data.posts.length > 0) {
-    params.set('before', data.posts[data.posts.length - 1].created_at);
+    filter.before = data.posts[data.posts.length - 1].created_at;
   }
-  await fetch(`/api/posts?${params}`)
-  .then(r => r.json())
-  .then((resp: Post[]) => {
+
+
+  fetchPosts(filter).then(resp => {
     if (resp.length > 0) {
       // Append old posts, filter dupes
       // There shouldn't be any duplicates, but better be safe than sorry
-      const combined = data.posts.concat(resp);
-      const filteredPosts = combined.filter((obj, index, arr) => {
-        return arr.map(mapObj => mapObj.url).indexOf(obj.url) === index;
-      });
-      data.posts = filteredPosts;
-      moreOlderPostsAvailable = true;
+      data.posts = filterDuplicates(data.posts.concat(resp));
+      // If we got less than we expected, there are no older posts available
+      moreOlderPostsAvailable = resp.length < (filter.count ?? 20);
     } else {
       moreOlderPostsAvailable = false;
     }