Frontend System Design: Facebook News Feed

This content originally appeared on DEV Community and was authored by ZeeshanAli-0704

🧠 System Design: Facebook News Feed (Frontend)

• System Design: Facebook News Feed (Frontend)
  • 1. General Requirements
  • 2. Component Architecture
    • Top Level Layout
    • Story Component StoryCard
    • Comment Component CommentList
    • Create Comment Component CreateComment
    • Component Hierarchy
  • 3. Data Entities
  • 4. Data APIs
  • 5. Data Store (Frontend State Management)
  • 6. Infinite Scrolling (Old Feeds)
  • 7. Real Time New Feeds via SSE
  • 8. Complete Feed Flow
  • 9. Optimization Strategies
    • A. Network Performance
    • B. Rendering Performance
    • C. JS Performance
  • 10. Accessibility (A11y)
  • 11. Example Flow: Combined Infinite Scroll SSE
  • 12. Endpoint Summary
  • Final Summary

1. 🎯 General Requirements

• Display feed/stories from people the user follows.
• User can create posts (text, image, video).
• Users can Like, Share, and Comment.

• Should support Infinite Scrolling:

  • Fetch older feeds as you scroll down.
  • Show new feeds in real-time (without refresh).

• Real time updates when:

  • New post is created.
  • Someone likes/comments on an existing post.

2. 🧩 Component Architecture

We’ll design a modular, maintainable component system.

Top Level Layout

• FeedPage

  • Manages initial data load, scrolling, and SSE subscription.
  • Renders a list of StoryCard components.

Story Component StoryCard

Responsibilities:

• Show user avatar, name, timestamp.
• Render post content (text/media).

• Include controls:

  • ❤️ Like
  • 💬 Comment
  • 🔁 Share

Sub-components:

• StoryHeader – avatar, name, timestamp
• StoryMedia – renders image/video
• StoryActions – like/share/comment buttons
• CommentList – render list of comments
• CreateComment – textbox + post button

Comment Component CommentList

• Displays all comments (virtualized for performance).

• Each comment has:

  • Avatar
  • Username
  • Comment text

Create Comment Component CreateComment

• Textarea + Post button.
• Emits comment creation event to parent (StoryCard).

🧠 Component Hierarchy

FeedPage
 ├── StoryCard
 │    ├── StoryHeader
 │    ├── StoryMedia
 │    ├── StoryActions
 │    ├── CommentList
 │    └── CreateComment
 └── InfiniteScrollLoader (sentinel element)

3. 🧱 Data Entities

type Media = {
  id: string;
  type: 'image' | 'video';
  url: string;
  thumbnail?: string;
};

type Comment = {
  id: string;
  user: { id: string; name: string; avatarUrl: string };
  text: string;
  createdAt: string;
};

type Story = {
  id: string;
  author: { id: string; name: string; avatarUrl: string };
  content: string;
  media?: Media[];
  likes: number;
  shares: number;
  comments: Comment[];
  createdAt: string;
};

4. 🔌 Data APIs

5. 🗂️ Data Store (Frontend State Management)

Use React Query, Zustand, or Redux Toolkit for reactive state.

State Structure:

{
  feed: {
    stories: Story[];
    cursor: string; // pagination cursor for older feeds
    loading: boolean;
  },
  newStoriesBuffer: Story[]; // for stories from SSE
  comments: { [storyId: string]: Comment[] },
  user: { id: string; name: string }
}

Behaviors:

• Optimistic Updates: Apply changes (likes/comments) instantly, rollback on failure.
• Normalized Storage: Map comments and stories by IDs.
• Buffer for SSE stories: Temporarily store new stories and show a “New Posts Available” banner.

6. 🔄 Infinite Scrolling (Old Feeds)

Use IntersectionObserver for older feed pagination.

Frontend Flow:

const sentinel = document.querySelector('#load-more');

const observer = new IntersectionObserver(async entries => {
  if (entries[0].isIntersecting) {
    await fetchOlderFeeds(); // REST API call
  }
});

observer.observe(sentinel);

API Example:

GET /api/feed?before=<oldest_story_id>&limit=10

Backend returns:

[
  { "id": 201, "author": "Zeeshan", "content": "Older post...", "createdAt": "..." }
]

7. ⚡ Real Time New Feeds via SSE

To get new stories without sockets, use Server-Sent Events (SSE).

Frontend:

// Connect to SSE endpoint
const eventSource = new EventSource('/api/feeds/stream');

eventSource.onmessage = (event) => {
  const newStory = JSON.parse(event.data);
  addToNewStoryBuffer(newStory); // Show "New posts available" banner
};

When user clicks “Show new posts” → prepend buffer to feed.

Backend SSE Endpoint:

app.get('/api/feeds/stream', (req, res) => {
  res.setHeader('Content-Type', 'text/event-stream');
  res.setHeader('Cache-Control', 'no-cache');
  res.flushHeaders();

  const sendStory = (story) => {
    res.write(`data: ${JSON.stringify(story)}\n\n`);
  };

  feedEmitter.on('newStory', sendStory);

  req.on('close', () => feedEmitter.off('newStory', sendStory));
});

Example Event Pushed:

data: {"id":302,"author":"Ali","content":"New post here!"}

8. 🧭 Complete Feed Flow

9. 🚀 Optimization Strategies

A. Network Performance

• Gzip/Brotli compression.
• WebP/AVIF images.
• Serve assets via CDN.
• Enable HTTP/2.
• Lazy load heavy media via IntersectionObserver.
• Bundle splitting: vendor vs. app bundles.

B. Rendering Performance

• Use SSR or hydration.
• Virtualized list rendering (React Window / VirtualScroller).
• Use defer/async for scripts.
• Memoize components and results.

C. JS Performance

• Debounce scroll handlers.
• Code-splitting by route.
• Offload heavy tasks to Web Workers.

10. 🧩 Accessibility (A11y)

• Semantic HTML: <article>, <header>, <section>, <button>.
• ARIA roles for live feed updates: aria-live="polite".
• Keyboard navigation.
• Alt text for media.
• High contrast colors.

11. 🧮 Example Flow: Combined Infinite Scroll + SSE

Scenario:

1. User opens app → GET /api/feed?limit=10
2. Scrolls to bottom → GET /api/feed?before=201&limit=10
3. Another user posts → Server sends SSE → data: {"id":305,"author":"Sara","content":"New story!"}
4. Frontend receives event → Shows “New posts available” banner.
5. User clicks → New story appears at top of feed.

12. 🧾 Endpoint Summary

✅ Final Summary

This content originally appeared on DEV Community and was authored by ZeeshanAli-0704

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ZeeshanAli-0704 | Sciencx (2025-10-31T14:40:25+00:00) Frontend System Design: Facebook News Feed. Retrieved from https://www.scien.cx/2025/10/31/frontend-system-design-facebook-news-feed/

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