feat: cursor-based pagination for comments using "Load more" button

fresh.gen.ts

@@ -38,8 +38,9 @@ import * as $32 from "./routes/submit/_middleware.tsx";
 import * as $33 from "./routes/submit/index.tsx";
 import * as $34 from "./routes/users/[login].tsx";
 import * as $$0 from "./islands/Chart.tsx";
-import * as $$1 from "./islands/PageInput.tsx";
-import * as $$2 from "./islands/VoteButton.tsx";
+import * as $$1 from "./islands/CommentsList.tsx";
+import * as $$2 from "./islands/PageInput.tsx";
+import * as $$3 from "./islands/VoteButton.tsx";
 
 const manifest = {
   routes: {
@@ -81,8 +82,9 @@ const manifest = {
   },
   islands: {
     "./islands/Chart.tsx": $$0,
-    "./islands/PageInput.tsx": $$1,
-    "./islands/VoteButton.tsx": $$2,
+    "./islands/CommentsList.tsx": $$1,
+    "./islands/PageInput.tsx": $$2,
+    "./islands/VoteButton.tsx": $$3,
   },
   baseUrl: import.meta.url,
 };

islands/CommentsList.tsx

@@ -0,0 +1,62 @@
+// Copyright 2023 the Deno authors. All rights reserved. MIT license.
+import { useSignal } from "@preact/signals";
+import { useEffect } from "preact/hooks";
+import { Comment } from "@/utils/db.ts";
+import UserPostedAt from "@/components/UserPostedAt.tsx";
+import { LINK_STYLES } from "@/utils/constants.ts";
+
+async function fetchComments(itemId: string, cursor: string) {
+  let url = `/api/items/${itemId}/comments`;
+  if (cursor !== "" && cursor !== undefined) url += "?cursor=" + cursor;
+  const resp = await fetch(url);
+  if (!resp.ok) throw new Error(`Request failed: GET ${url}`);
+  return await resp.json() as { comments: Comment[]; cursor: string };
+}
+
+function CommentSummary(props: Comment) {
+  return (
+    <div class="py-4">
+      <UserPostedAt {...props} />
+      <p>{props.text}</p>
+    </div>
+  );
+}
+
+export default function CommentsList(props: { itemId: string }) {
+  const commentsSig = useSignal<Comment[]>([]);
+  const cursorSig = useSignal("");
+  const isLoadingSig = useSignal(false);
+
+  async function loadMoreComments() {
+    isLoadingSig.value = true;
+    try {
+      const { comments, cursor } = await fetchComments(
+        props.itemId,
+        cursorSig.value,
+      );
+      commentsSig.value = [...commentsSig.value, ...comments];
+      cursorSig.value = cursor;
+    } catch (error) {
+      console.log(error.message);
+    } finally {
+      isLoadingSig.value = false;
+    }
+  }
+
+  useEffect(() => {
+    loadMoreComments();
+  }, []);
+
+  return (
+    <div>
+      {commentsSig.value.map((comment) => (
+        <CommentSummary key={comment.id} {...comment} />
+      ))}
+      {cursorSig.value !== "" && !isLoadingSig.value && (
+        <button onClick={loadMoreComments} class={LINK_STYLES}>
+          Load more
+        </button>
+      )}
+    </div>
+  );
+}

main.ts

@@ -25,7 +25,7 @@ if (Deno.env.get("RESET_DENO_KV") === "1") {
 /**
  * @todo Remove at v1. This is a quick way to migrate Deno KV, as database changes are likely to occur and require adjustment.
  */
-if (Deno.env.get("MIGRATE_DENO_KEY") === "1") {
+if (Deno.env.get("MIGRATE_DENO_KV") === "1") {
   await migrateKv();
 }
 

routes/items/[id].tsx

@@ -1,25 +1,22 @@
 // Copyright 2023 the Deno authors. All rights reserved. MIT license.
 import type { Handlers, RouteContext } from "$fresh/server.ts";
 import ItemSummary from "@/components/ItemSummary.tsx";
-import PageSelector from "@/components/PageSelector.tsx";
 import { BUTTON_STYLES, INPUT_STYLES } from "@/utils/constants.ts";
-import { calcLastPage, calcPageNum, PAGE_LENGTH } from "@/utils/pagination.ts";
 import {
   type Comment,
   createComment,
   createNotification,
   getAreVotedBySessionId,
-  getCommentsByItem,
   getItem,
   getUserBySession,
   newCommentProps,
   newNotificationProps,
   Notification,
 } from "@/utils/db.ts";
-import UserPostedAt from "@/components/UserPostedAt.tsx";
 import { redirect } from "@/utils/redirect.ts";
 import Head from "@/components/Head.tsx";
 import { SignedInState } from "@/utils/middleware.ts";
+import CommentsList from "@/islands/CommentsList.tsx";
 
 export const handler: Handlers<unknown, SignedInState> = {
   async POST(req, ctx) {
@@ -75,39 +72,19 @@ function CommentInput() {
   );
 }
 
-function CommentSummary(comment: Comment) {
-  return (
-    <div class="py-4">
-      <UserPostedAt
-        userLogin={comment.userLogin}
-        createdAt={comment.createdAt}
-      />
-      <p>{comment.text}</p>
-    </div>
-  );
-}
-
 export default async function ItemsItemPage(
   _req: Request,
   ctx: RouteContext<undefined, SignedInState>,
 ) {
-  const { id } = ctx.params;
-  const item = await getItem(id);
+  const itemId = ctx.params.id;
+  const item = await getItem(itemId);
   if (item === null) return await ctx.renderNotFound();
 
-  const pageNum = calcPageNum(ctx.url);
-  const allComments = await getCommentsByItem(id);
-  const comments = allComments
-    .sort((a, b) => b.createdAt.getTime() - a.createdAt.getTime())
-    .slice((pageNum - 1) * PAGE_LENGTH, pageNum * PAGE_LENGTH);
-
   const [isVoted] = await getAreVotedBySessionId(
     [item],
     ctx.state.sessionId,
   );
 
-  const lastPage = calcLastPage(allComments.length, PAGE_LENGTH);
-
   return (
     <>
       <Head title={item.title} href={ctx.url.href} />
@@ -117,19 +94,7 @@ export default async function ItemsItemPage(
           isVoted={isVoted}
         />
         <CommentInput />
-        <div>
-          {comments.map((comment) => (
-            <CommentSummary
-              {...comment}
-            />
-          ))}
-        </div>
-        {lastPage > 1 && (
-          <PageSelector
-            currentPage={calcPageNum(ctx.url)}
-            lastPage={lastPage}
-          />
-        )}
+        <CommentsList itemId={ctx.params.id} />
       </main>
     </>
   );

utils/db.ts

@@ -27,7 +27,7 @@ async function getValues<T>(
 ) {
   const values = [];
   const iter = kv.list<T>(selector, options);
-  for await (const { value } of iter) values.push(value);
+  for await (const entry of iter) values.push(entry.value);
   return values;
 }
 
@@ -335,10 +335,6 @@ export async function deleteComment(comment: Comment) {
   if (!res.ok) throw new Error(`Failed to delete comment: ${comment}`);
 }
 
-export async function getCommentsByItem(itemId: string) {
-  return await getValues<Comment>({ prefix: ["comments_by_item", itemId] });
-}
-
 export function listCommentsByItem(
   itemId: string,
   options?: Deno.KvListOptions,

utils/db_test.ts

@@ -1,5 +1,6 @@
 // Copyright 2023 the Deno authors. All rights reserved. MIT license.
 import {
+  collectValues,
   type Comment,
   compareScore,
   createComment,
@@ -15,7 +16,6 @@ import {
   formatDate,
   getAllItems,
   getAreVotedBySessionId,
-  getCommentsByItem,
   getDatesSince,
   getItem,
   getItemsByUser,
@@ -30,6 +30,7 @@ import {
   ifUserHasNotifications,
   incrVisitsCountByDay,
   type Item,
+  listCommentsByItem,
   newCommentProps,
   newItemProps,
   newNotificationProps,
@@ -191,16 +192,19 @@ Deno.test("[db] (create/delete)Comment() + getCommentsByItem()", async () => {
   const comment1 = { ...genNewComment(), itemId };
   const comment2 = { ...genNewComment(), itemId };
 
-  assertEquals(await getCommentsByItem(itemId), []);
+  assertEquals(await collectValues(listCommentsByItem(itemId)), []);
 
   await createComment(comment1);
   await createComment(comment2);
   await assertRejects(async () => await createComment(comment2));
-  assertArrayIncludes(await getCommentsByItem(itemId), [comment1, comment2]);
+  assertArrayIncludes(await collectValues(listCommentsByItem(itemId)), [
+    comment1,
+    comment2,
+  ]);
 
   await deleteComment(comment1);
   await deleteComment(comment2);
-  assertEquals(await getCommentsByItem(itemId), []);
+  assertEquals(await collectValues(listCommentsByItem(itemId)), []);
 });
 
 Deno.test("[db] votes", async () => {