Designing a News Feed is one of those problems that looks simple until you actually start building it. Underneath the scrolling posts and likes are dozens of decisions — how to manage state, what rendering model to use, and how to make updates instant without losing consistency.

In this post, we’ll walk through how to design a scalable News Feed frontend — using the RCADO structure as a thinking guide.

R — Requirements

What to Explain

In an interview, this is where you clarify the scope, goals, and constraints before jumping into architecture.
Interviewers expect you to ask questions and define boundaries instead of jumping straight into solutions.

Functional Requirements

  • View a scrollable list of posts (from user and friends).
  • Create and publish new posts.
  • Like and comment on posts.
  • Load additional posts on scroll or via “load more” button.
  • Handle updates (e.g., new likes or comments).

Non-Functional Requirements

  • Responsive and mobile-friendly.
  • Fast initial load and smooth interactions.
  • Accessible to all users (ARIA, keyboard navigation).
  • Secure against client-side attacks.
  • Support localization and multiple languages.
  • Optionally work offline or in poor network conditions.

Interview Tip:
Explain the difference between functional (“what the system does”) and non-functional (“how well it does it”). Most candidates skip this — doing so instantly makes your approach structured.

C — Components

What to Explain

Here, focus on UI breakdown, state ownership, and data flow between components. Interviewers care about how you translate requirements into a maintainable component tree.

Component

Props

Responsibility

Feed

posts, onLoadMore

Owns the post list, handles pagination, fetch, and updates.

PostCard

post, onLike, onComment

Displays a single post (author, content, likes, comments).

LikeButton

liked, onToggle

Handles toggling of like state and visual feedback.

CommentSection

comments, onAddComment

Renders all comments related to a post.

CommentComposer

onSubmit

Manages input for adding a new comment.

PostComposer

onSubmit, initialText?

Text/image input area for creating new posts.

Ownership & Flow

  • Feed owns and updates the posts array.
  • PostCard is mostly presentational.
  • CommentSection has isolated state for comment list and input.
  • Top-down data, bottom-up actions keep updates predictable.

FeedPost composerEditor (Lexical)PostMedia uploadLike ButtonComment composer


Interview Tip:
Explain why a component owns certain data. For example, “Feed owns the posts because it fetches them and handles pagination. Individual PostCards only need to render their portion of that data.”

A — Architecture

What to Explain

Here, focus on rendering, routing, and state/data management choices.
Interviewers want to see that you understand trade-offs — not just frameworks.

Rendering Approaches

Rendering defines how HTML gets to the user. There are four major patterns:

Method

Description

Pros

Cons

Server-Side Rendering (SSR)

Server sends HTML before JavaScript runs.

Fast initial load, good for SEO.

Slower interactivity, more server load.

Client-Side Rendering (CSR)

Browser loads JS, then builds DOM dynamically.

Great for interactivity and dynamic UIs.

Slower first paint, bad for SEO.

Static Site Generation (SSG)

Pages pre-built during deployment.

Fast for static content.

Not suitable for dynamic feeds.

Hybrid Rendering (SSR + Hydration)

Initial page via SSR, then client JS takes over.

Combines SEO + interactivity.

Slightly more complex setup.

Choice:
For a dynamic feed (frequent updates, infinite scroll), Hybrid Rendering is ideal.
It gives users instant visual feedback while enabling real-time interactions after hydration.
👉 You can read more about rendering strategies [here].

Single Page vs Multi Page

Type

Description

Pros

Cons

Single Page Application (SPA)

Entire app loads once; navigation handled client-side.

Smooth transitions, less reload.

Larger bundle size, needs good caching.

Multi Page Application (MPA)

Each page reloads independently.

Simple architecture, SEO-friendly.

Full reloads between pages.

Choice:
A News Feed is inherently SPA-friendly, since scrolling, liking, and commenting all happen dynamically without navigation.
You can, however, combine SPA routing with SSR for hybrid optimization.
(Learn more about SPA vs MPA [here].)

State Management

When building a feed, different states coexist. Interviewers expect you to reason through which state belongs where and why.

Type

Description

Where It Lives

Local State

Short-lived data like form input, modals, toggles.

Component-level.

Global State

Shared data across components (user info, theme).

Central store or dependency injection.

Server State

Data from APIs that needs caching and synchronization.

Network layer with caching.

Persistent State

Data saved locally for offline or quick access.

IndexedDB, localStorage, or service worker cache.

Choice:
Feed data = server state,
UI toggles (like modals) = local state,
User session = global state,
Offline cache = persistent state.

This separation avoids unwanted side effects and makes debugging easier.
Read more about frontend state models [here].

Communication & Pagination

Two main pagination methods exist:

Type

How It Works

Pros

Cons

Offset-based

Fetches data using page numbers (?page=2&limit=10).

Easy to implement.

Can duplicate or skip data if posts are updated.

Cursor-based

Uses a unique key (?cursor=xyz) to fetch next results.

More accurate and scalable.

Slightly complex to manage.

Choice:
Feeds evolve in real time — posts can appear or disappear.
So cursor-based pagination ensures smooth infinite scroll and consistent ordering, avoiding duplicate or missing data.
Learn more about pagination types [here].

Routing

For feeds, the following routes are typical:

Route

Primary Resource / Data Owner

Responsibility & Feature Mapping

/feed

Global Feed Data

Owns the master list of posts. Manages global pagination state (cursor/page).

/post/:id

Single Post Data

Fetches the full post object using the :id. This is the canonical data source for all nested features.

/profile/:id

User's Post Feed Data

Owns the list of posts filtered by the user :id. Manages profile-specific pagination.

/comments/:postId

Post's Comment Data (nested resource)

Mapped to /post/:id context. The CommentSection component handles nested pagination and all related API interactions (fetch/add).

/likes/:postId

Post's Reaction Data (nested resource)

Mapped to /post/:id context (data update). The LikeButton component handles optimistic updates of likesCount and likedByUser via API (e.g., POST /api/post/:id/like).


Interviewers expect clarity in which route owns which data (e.g., /feed handles global pagination, /post/:id fetches a single post).

D — Data Model

What to Explain

Discuss data structure design, ownership, and synchronization flow between client and server. Interviewers look for clarity and reactivity, not raw schema.

type User = {
id: string
name: string
avatar: string
}

type Comment = {
id: string
postId: string
author: User
content: string
createdAt: string
}

type Post = {
id: string
author: User
content: string
image?: string
likes: number
likedByUser: boolean
comments: Comment[]
createdAt: string
}

Ownership

  • Feed → owns list of posts.
  • PostCard → owns individual post and likes.
  • CommentSection → owns its list of comments.

Data Flow

  1. Fetch feed data (paginated).
  2. Render list of posts.
  3. When user likes or comments, apply optimistic update locally.
  4. Sync with server → confirm or rollback.

This ensures low latency for users while maintaining consistency across sessions.

Interview Tip:
Explain why optimistic updates matter: they make UIs feel instant and responsive, even if the network is slow.

O — Other (Performance, Accessibility, Security)

What to Explain

This is where you show depth — performance, accessibility, and security often distinguish senior-level answers.

Performance

  • Virtualized rendering for large lists (e.g., 1000+ posts).
  • Prefetch upcoming data before user scrolls to bottom.
  • Lazy-load comments and media only when needed.
  • Debounce expensive actions like search or scroll listeners.
  • Split code by routes or components to optimize bundle size.
    You can read more about feed optimization [here].

Accessibility

  • Semantic elements: <article> for posts, <section> for comments.
  • Proper ARIA roles (role="feed", role="article").
  • Focus management for modal composers.
  • Keyboard-friendly actions for like/comment.
  • Maintain color contrast and text size.

Security

  • Sanitize all user input before rendering.
  • Escape dynamic content to avoid XSS.
  • Use secure cookies or memory for auth tokens.
  • Prevent CSRF via anti-forgery tokens.
  • Disable inline JS execution.

Interview Tip:
Briefly tie these back to your design — e.g., “Since users can post HTML content, sanitization at render time is mandatory.”