refactor: update auto scroll mechanism (#970)

biome.jsonc

@@ -54,7 +54,8 @@
         "noUselessStringConcat": "warn", // Not in recommended ruleset, turning on manually
         "noForEach": "off", // forEach is too familiar to ban
         "noUselessSwitchCase": "off", // Turned off due to developer preferences
-        "noUselessThisAlias": "off" // Turned off due to developer preferences
+        "noUselessThisAlias": "off", // Turned off due to developer preferences
+        "noBannedTypes": "off"
       },
       "correctness": {
         "noUnusedImports": "warn", // Not in recommended ruleset, turning on manually

components/artifact-messages.tsx

@@ -1,11 +1,12 @@
-import { PreviewMessage } from './message';
-import { useScrollToBottom } from './use-scroll-to-bottom';
-import { Vote } from '@/lib/db/schema';
-import { UIMessage } from 'ai';
+import { PreviewMessage, ThinkingMessage } from './message';
+import type { Vote } from '@/lib/db/schema';
+import type { UIMessage } from 'ai';
 import { memo } from 'react';
 import equal from 'fast-deep-equal';
-import { UIArtifact } from './artifact';
-import { UseChatHelpers } from '@ai-sdk/react';
+import type { UIArtifact } from './artifact';
+import type { UseChatHelpers } from '@ai-sdk/react';
+import { motion } from 'framer-motion';
+import { useMessages } from '@/hooks/use-messages';
 
 interface ArtifactMessagesProps {
   chatId: string;
@@ -27,8 +28,16 @@ function PureArtifactMessages({
   reload,
   isReadonly,
 }: ArtifactMessagesProps) {
-  const [messagesContainerRef, messagesEndRef] =
-    useScrollToBottom<HTMLDivElement>();
+  const {
+    containerRef: messagesContainerRef,
+    endRef: messagesEndRef,
+    onViewportEnter,
+    onViewportLeave,
+    hasSentMessage,
+  } = useMessages({
+    chatId,
+    status,
+  });
 
   return (
     <div
@@ -49,12 +58,21 @@ function PureArtifactMessages({
           setMessages={setMessages}
           reload={reload}
           isReadonly={isReadonly}
+          requiresScrollPadding={
+            hasSentMessage && index === messages.length - 1
+          }
         />
       ))}
 
-      <div
+      {status === 'submitted' &&
+        messages.length > 0 &&
+        messages[messages.length - 1].role === 'user' && <ThinkingMessage />}
+
+      <motion.div
         ref={messagesEndRef}
         className="shrink-0 min-w-[24px] min-h-[24px]"
+        onViewportLeave={onViewportLeave}
+        onViewportEnter={onViewportEnter}
       />
     </div>
   );

components/artifact.tsx

@@ -26,7 +26,7 @@ import { codeArtifact } from '@/artifacts/code/client';
 import { sheetArtifact } from '@/artifacts/sheet/client';
 import { textArtifact } from '@/artifacts/text/client';
 import equal from 'fast-deep-equal';
-import { UseChatHelpers } from '@ai-sdk/react';
+import type { UseChatHelpers } from '@ai-sdk/react';
 
 export const artifactDefinitions = [
   textArtifact,
@@ -309,7 +309,7 @@ function PureArtifact({
                 )}
               </AnimatePresence>
 
-              <div className="flex flex-col h-full justify-between items-center gap-4">
+              <div className="flex flex-col h-full justify-between items-center">
                 <ArtifactMessages
                   chatId={chatId}
                   status={status}

components/message.tsx

@@ -28,6 +28,7 @@ const PurePreviewMessage = ({
   setMessages,
   reload,
   isReadonly,
+  requiresScrollPadding,
 }: {
   chatId: string;
   message: UIMessage;
@@ -36,6 +37,7 @@ const PurePreviewMessage = ({
   setMessages: UseChatHelpers['setMessages'];
   reload: UseChatHelpers['reload'];
   isReadonly: boolean;
+  requiresScrollPadding: boolean;
 }) => {
   const [mode, setMode] = useState<'view' | 'edit'>('view');
 
@@ -65,7 +67,11 @@ const PurePreviewMessage = ({
             </div>
           )}
 
-          <div className="flex flex-col gap-4 w-full">
+          <div
+            className={cn('flex flex-col gap-4 w-full', {
+              'min-h-96': message.role === 'assistant' && requiresScrollPadding,
+            })}
+          >
             {message.experimental_attachments &&
               message.experimental_attachments.length > 0 && (
                 <div
@@ -236,6 +242,8 @@ export const PreviewMessage = memo(
   (prevProps, nextProps) => {
     if (prevProps.isLoading !== nextProps.isLoading) return false;
     if (prevProps.message.id !== nextProps.message.id) return false;
+    if (prevProps.requiresScrollPadding !== nextProps.requiresScrollPadding)
+      return false;
     if (!equal(prevProps.message.parts, nextProps.message.parts)) return false;
     if (!equal(prevProps.vote, nextProps.vote)) return false;
 
@@ -249,7 +257,7 @@ export const ThinkingMessage = () => {
   return (
     <motion.div
       data-testid="message-assistant-loading"
-      className="w-full mx-auto max-w-3xl px-4 group/message "
+      className="w-full mx-auto max-w-3xl px-4 group/message min-h-96"
       initial={{ y: 5, opacity: 0 }}
       animate={{ y: 0, opacity: 1, transition: { delay: 1 } }}
       data-role={role}

components/messages.tsx

@@ -1,11 +1,12 @@
 import type { UIMessage } from 'ai';
 import { PreviewMessage, ThinkingMessage } from './message';
-import { useScrollToBottom } from './use-scroll-to-bottom';
 import { Greeting } from './greeting';
 import { memo } from 'react';
 import type { Vote } from '@/lib/db/schema';
 import equal from 'fast-deep-equal';
 import type { UseChatHelpers } from '@ai-sdk/react';
+import { motion } from 'framer-motion';
+import { useMessages } from '@/hooks/use-messages';
 
 interface MessagesProps {
   chatId: string;
@@ -27,13 +28,21 @@ function PureMessages({
   reload,
   isReadonly,
 }: MessagesProps) {
-  const [messagesContainerRef, messagesEndRef] =
-    useScrollToBottom<HTMLDivElement>();
+  const {
+    containerRef: messagesContainerRef,
+    endRef: messagesEndRef,
+    onViewportEnter,
+    onViewportLeave,
+    hasSentMessage,
+  } = useMessages({
+    chatId,
+    status,
+  });
 
   return (
     <div
       ref={messagesContainerRef}
-      className="flex flex-col min-w-0 gap-6 flex-1 overflow-y-scroll pt-4"
+      className="flex flex-col min-w-0 gap-6 flex-1 overflow-y-scroll pt-4 relative"
     >
       {messages.length === 0 && <Greeting />}
 
@@ -51,6 +60,9 @@ function PureMessages({
           setMessages={setMessages}
           reload={reload}
           isReadonly={isReadonly}
+          requiresScrollPadding={
+            hasSentMessage && index === messages.length - 1
+          }
         />
       ))}
 
@@ -58,9 +70,11 @@ function PureMessages({
         messages.length > 0 &&
         messages[messages.length - 1].role === 'user' && <ThinkingMessage />}
 
-      <div
+      <motion.div
         ref={messagesEndRef}
         className="shrink-0 min-w-[24px] min-h-[24px]"
+        onViewportLeave={onViewportLeave}
+        onViewportEnter={onViewportEnter}
       />
     </div>
   );

components/multimodal-input.tsx

@@ -23,6 +23,9 @@ import { Textarea } from './ui/textarea';
 import { SuggestedActions } from './suggested-actions';
 import equal from 'fast-deep-equal';
 import type { UseChatHelpers } from '@ai-sdk/react';
+import { AnimatePresence, motion } from 'framer-motion';
+import { ArrowDown } from 'lucide-react';
+import { useScrollToBottom } from '@/hooks/use-scroll-to-bottom';
 
 function PureMultimodalInput({
   chatId,
@@ -179,8 +182,41 @@ function PureMultimodalInput({
     [setAttachments],
   );
 
+  const { isAtBottom, scrollToBottom } = useScrollToBottom();
+
+  useEffect(() => {
+    if (status === 'submitted') {
+      scrollToBottom();
+    }
+  }, [status, scrollToBottom]);
+
   return (
     <div className="relative w-full flex flex-col gap-4">
+      <AnimatePresence>
+        {!isAtBottom && (
+          <motion.div
+            initial={{ opacity: 0, y: 10 }}
+            animate={{ opacity: 1, y: 0 }}
+            exit={{ opacity: 0, y: 10 }}
+            transition={{ type: 'spring', stiffness: 300, damping: 20 }}
+            className="absolute left-1/2 bottom-28 -translate-x-1/2 z-50"
+          >
+            <Button
+              data-testid="scroll-to-bottom-button"
+              className="rounded-full"
+              size="icon"
+              variant="outline"
+              onClick={(event) => {
+                event.preventDefault();
+                scrollToBottom();
+              }}
+            >
+              <ArrowDown />
+            </Button>
+          </motion.div>
+        )}
+      </AnimatePresence>
+
       {messages.length === 0 &&
         attachments.length === 0 &&
         uploadQueue.length === 0 && (

components/use-scroll-to-bottom.ts

@@ -1,31 +0,0 @@
-import { useEffect, useRef, type RefObject } from 'react';
-
-export function useScrollToBottom<T extends HTMLElement>(): [
-  RefObject<T>,
-  RefObject<T>,
-] {
-  const containerRef = useRef<T>(null);
-  const endRef = useRef<T>(null);
-
-  useEffect(() => {
-    const container = containerRef.current;
-    const end = endRef.current;
-
-    if (container && end) {
-      const observer = new MutationObserver(() => {
-        end.scrollIntoView({ behavior: 'instant', block: 'end' });
-      });
-
-      observer.observe(container, {
-        childList: true,
-        subtree: true,
-        attributes: true,
-        characterData: true,
-      });
-
-      return () => observer.disconnect();
-    }
-  }, []);
-
-  return [containerRef, endRef];
-}

hooks/use-messages.tsx

@@ -0,0 +1,45 @@
+import { useState, useEffect } from 'react';
+import { useScrollToBottom } from './use-scroll-to-bottom';
+import type { UseChatHelpers } from '@ai-sdk/react';
+
+export function useMessages({
+  chatId,
+  status,
+}: {
+  chatId: string;
+  status: UseChatHelpers['status'];
+}) {
+  const {
+    containerRef,
+    endRef,
+    isAtBottom,
+    scrollToBottom,
+    onViewportEnter,
+    onViewportLeave,
+  } = useScrollToBottom();
+
+  const [hasSentMessage, setHasSentMessage] = useState(false);
+
+  useEffect(() => {
+    if (chatId) {
+      scrollToBottom('instant');
+      setHasSentMessage(false);
+    }
+  }, [chatId, scrollToBottom]);
+
+  useEffect(() => {
+    if (status === 'submitted') {
+      setHasSentMessage(true);
+    }
+  }, [status]);
+
+  return {
+    containerRef,
+    endRef,
+    isAtBottom,
+    scrollToBottom,
+    onViewportEnter,
+    onViewportLeave,
+    hasSentMessage,
+  };
+}

hooks/use-scroll-to-bottom.tsx

@@ -0,0 +1,49 @@
+import useSWR from 'swr';
+import { useRef, useEffect, useCallback } from 'react';
+
+type ScrollFlag = ScrollBehavior | false;
+
+export function useScrollToBottom() {
+  const containerRef = useRef<HTMLDivElement>(null);
+  const endRef = useRef<HTMLDivElement>(null);
+
+  const { data: isAtBottom = false, mutate: setIsAtBottom } = useSWR(
+    'messages:is-at-bottom',
+    null,
+    { fallbackData: false },
+  );
+
+  const { data: scrollBehavior = false, mutate: setScrollBehavior } =
+    useSWR<ScrollFlag>('messages:should-scroll', null, { fallbackData: false });
+
+  useEffect(() => {
+    if (scrollBehavior) {
+      endRef.current?.scrollIntoView({ behavior: scrollBehavior });
+      setScrollBehavior(false);
+    }
+  }, [setScrollBehavior, scrollBehavior]);
+
+  const scrollToBottom = useCallback(
+    (scrollBehavior: ScrollBehavior = 'smooth') => {
+      setScrollBehavior(scrollBehavior);
+    },
+    [setScrollBehavior],
+  );
+
+  function onViewportEnter() {
+    setIsAtBottom(true);
+  }
+
+  function onViewportLeave() {
+    setIsAtBottom(false);
+  }
+
+  return {
+    containerRef,
+    endRef,
+    isAtBottom,
+    scrollToBottom,
+    onViewportEnter,
+    onViewportLeave,
+  };
+}

package.json

@@ -1,6 +1,6 @@
 {
   "name": "ai-chatbot",
-  "version": "3.0.14",
+  "version": "3.0.15",
   "private": true,
   "scripts": {
     "dev": "next dev --turbo",

tests/e2e/chat.test.ts

@@ -150,4 +150,21 @@ test.describe('Chat activity', () => {
     const assistantMessage = await chatPage.getRecentAssistantMessage();
     expect(assistantMessage.content).toContain("It's just blue duh!");
   });
+
+  test('auto-scrolls to bottom after submitting new messages', async () => {
+    await chatPage.sendMultipleMessages(5, (i) => `filling message #${i}`);
+    await chatPage.waitForScrollToBottom();
+  });
+
+  test('scroll button appears when user scrolls up, hides on click', async () => {
+    await chatPage.sendMultipleMessages(5, (i) => `filling message #${i}`);
+    await expect(chatPage.scrollToBottomButton).not.toBeVisible();
+
+    await chatPage.scrollToTop();
+    await expect(chatPage.scrollToBottomButton).toBeVisible();
+
+    await chatPage.scrollToBottomButton.click();
+    await chatPage.waitForScrollToBottom();
+    await expect(chatPage.scrollToBottomButton).not.toBeVisible();
+  });
 });

tests/fixtures.ts

@@ -8,7 +8,7 @@ interface Fixtures {
   curieContext: UserContext;
 }
 
-export const test = baseTest.extend<any, Fixtures>({
+export const test = baseTest.extend<{}, Fixtures>({
   adaContext: [
     async ({ browser }, use, workerInfo) => {
       const ada = await createAuthenticatedContext({

tests/pages/chat.ts

@@ -18,6 +18,14 @@ export class ChatPage {
     return this.page.getByTestId('multimodal-input');
   }
 
+  public get scrollContainer() {
+    return this.page.locator('.overflow-y-scroll');
+  }
+
+  public get scrollToBottomButton() {
+    return this.page.getByTestId('scroll-to-bottom-button');
+  }
+
   async createNewChat() {
     await this.page.goto('/');
   }
@@ -195,4 +203,37 @@ export class ChatPage {
     const sidebarToggleButton = this.page.getByTestId('sidebar-toggle-button');
     await sidebarToggleButton.click();
   }
+
+  public async isScrolledToBottom(): Promise<boolean> {
+    return this.scrollContainer.evaluate(
+      (el) => Math.abs(el.scrollHeight - el.scrollTop - el.clientHeight) < 1,
+    );
+  }
+
+  public async waitForScrollToBottom(timeout = 5_000): Promise<void> {
+    const start = Date.now();
+
+    while (Date.now() - start < timeout) {
+      if (await this.isScrolledToBottom()) return;
+      await this.page.waitForTimeout(100);
+    }
+
+    throw new Error(`Timed out waiting for scroll bottom after ${timeout}ms`);
+  }
+
+  public async sendMultipleMessages(
+    count: number,
+    makeMessage: (i: number) => string,
+  ) {
+    for (let i = 0; i < count; i++) {
+      await this.sendUserMessage(makeMessage(i));
+      await this.isGenerationComplete();
+    }
+  }
+
+  public async scrollToTop(): Promise<void> {
+    await this.scrollContainer.evaluate((element) => {
+      element.scrollTop = 0;
+    });
+  }
 }