Frontend System Design Mastery Roadmap

Table of Contents

RADIO Framework - Interview Approach

1. Networking
2. Communication
3. Security
4. Testing
5. Performance
6. Database & Caching
7. Logging & Monitoring
8. Accessibility
9. Offline Support
10. Low-Level Design (LLD)
11. High-Level Design (HLD)
12. Modern Frontend Architecture
13. DevOps & Deployment
14. Advanced Topics
15. Soft Skills & Career
16. Appendix: Resources
17. Study Approach

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RADIO Framework - Interview Approach

A structured approach to ace frontend system design interviews.

What is RADIO?

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R - Requirements Exploration (~15%)

Objective: Understand the problem and determine scope through clarifying questions.

Key Questions to Ask:

• What are the main use cases and core features?
• What are the functional vs non-functional requirements?
• Which features are core vs nice-to-have?
• What devices/platforms need support (desktop/mobile/tablet)?
• Is offline support necessary?
• Who are the primary users?
• Any specific performance requirements?

Example: Design Facebook News Feed

• Focus on: News feed display, creating posts, pagination
• Functional: View feed, create posts, like/react
• Non-functional: Fast loading, smooth scrolling, real-time updates
• Core features: Text posts, images, reactions
• Nice-to-have: Videos, polls, location check-ins

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A - Architecture / High-Level Design (~20%)

Objective: Identify key components and their relationships.

Common Components:

• Server - Backend APIs (black box)
• Controller - Handles user interactions and data flow
• Model/Store - Client-side data storage
• View - UI components

Example Architecture: Facebook News Feed

Component Responsibilities:

• Server: Provides feed data, creates new posts
• Controller: Manages API calls, data transformation
• Client Store: Caches user data, feed posts
• Feed UI: Renders post list and composer
• Feed Post: Displays individual post with interactions
• Post Composer: Interface for creating new posts

---

D - Data Model / Core Entities (~10%)

Objective: Define data entities, fields, and ownership.

Data Types:

• Server-originated: From database (user profiles, posts)
• Client-only: Local state (form inputs, UI state)

Example Data Model: News Feed

Source	Entity	Component	Fields
Server	Post	Feed Post	id, created_time, content, image, author (User), reactions
Server	Feed	Feed UI	posts[], pagination (cursor, hasNext)
Server	User	Client Store	id, name, profile_photo_url
Client	NewPost	Composer	message, image, isDraft
Client	UI State	Feed UI	isLoading, error, selectedTab

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I - Interface Definition (API) (~15%)

Objective: Define APIs between components - their functionality, parameters, and responses.

Server-Client API Example

Fetch Feed Posts

// API Specification
GET /feed

// Parameters
{
  "size": 10,
  "cursor": "dXNlcjpXMDdRQ1JQQTQ"
}

// Response
{
  "pagination": {
    "size": 10,
    "next_cursor": "dXNlcjpVMEc5V0ZYTlo",
    "has_next": true
  },
  "results": [
    {
      "id": "123",
      "author": {
        "id": "456",
        "name": "John Doe",
        "profile_photo": "https://example.com/photo.jpg"
      },
      "content": "Hello world!",
      "image": "https://example.com/post.jpg",
      "reactions": {
        "likes": 20,
        "loves": 5
      },
      "created_time": 1620639583
    }
  ]
}

Create New Post

POST /posts

// Parameters
{
  "content": "My new post",
  "image": "base64_encoded_image",
  "visibility": "public"
}

// Response
{
  "id": "789",
  "status": "published",
  "created_time": 1620639999
}

Client-Client API Example

// Controller to Store
function addPostToFeed(post: Post): void

// Controller to View
function updateFeedUI(posts: Post[], isLoading: boolean): void

// Composer to Controller
function submitNewPost(content: string, image?: File): Promise<Post>

---

O - Optimizations & Deep Dive (~40%)

Objective: Discuss optimizations and dive deep into critical areas.

Focus Areas (choose based on product needs):

1. Performance

• Initial Load: Code splitting, lazy loading, SSR
• Runtime: Virtual scrolling for long feeds
• Images: Lazy loading, responsive images, WebP format
• Caching: Service workers, HTTP caching

2. User Experience

• Optimistic Updates: Show post immediately, rollback on error
• Skeleton Screens: Show loading placeholders
• Infinite Scroll: Intersection Observer for pagination
• Pull-to-Refresh: Mobile gesture support

3. Network

• Request Batching: Combine multiple API calls
• Debouncing: Limit API calls for search/autocomplete
• Retry Logic: Handle network failures gracefully
• WebSockets: Real-time updates for new posts

4. Accessibility

• Keyboard Navigation: Tab through posts, shortcuts
• Screen Readers: ARIA labels, semantic HTML
• Focus Management: Maintain focus after interactions
• Color Contrast: WCAG AA/AAA compliance

5. Scalability

• Pagination Strategy: Cursor-based for infinite scroll
• State Management: Redux/Zustand for complex apps
• Component Reusability: Atomic design principles

6. Security

• XSS Prevention: Sanitize user input
• CSRF Protection: Token-based validation
• Content Security Policy: Restrict resource loading

---

Example Deep Dive: Infinite Scroll Implementation

// Using Intersection Observer for efficient infinite scroll
const FeedComponent = () => {
  const [posts, setPosts] = useState([]);
  const [cursor, setCursor] = useState(null);
  const [isLoading, setIsLoading] = useState(false);
  const observerTarget = useRef(null);

  useEffect(() => {
    const observer = new IntersectionObserver(
      entries => {
        if (entries[0].isIntersecting && !isLoading && cursor) {
          loadMorePosts();
        }
      },
      { threshold: 0.5 }
    );

    if (observerTarget.current) {
      observer.observe(observerTarget.current);
    }

    return () => observer.disconnect();
  }, [cursor, isLoading]);

  const loadMorePosts = async () => {
    setIsLoading(true);
    const data = await fetchFeed({ cursor, size: 10 });
    setPosts(prev => [...prev, ...data.results]);
    setCursor(data.pagination.next_cursor);
    setIsLoading(false);
  };

  return (
    <div>
      {posts.map(post => (
        <PostCard key={post.id} post={post} />
      ))}
      <div ref={observerTarget} />
      {isLoading && <Skeleton />}
    </div>
  );
};

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RADIO Framework Summary

Step	Duration	Key Focus
Requirements	<15%	Clarify scope, features, constraints
Architecture	~20%	Component diagram, relationships
Data Model	~10%	Entities, fields, data flow
Interface	~15%	APIs, parameters, responses
Optimizations	~40%	Performance, UX, scalability

Pro Tips:

• Write down requirements for reference
• Draw diagrams for architecture
• Choose optimization topics based on product type and your strengths
• Show depth over breadth in the deep dive section

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1. Networking

Introduction

• Important Guidelines
• Network Fundamentals
• Browser Networking APIs

Core Concepts

• How the Web Works
  • DNS Resolution
  • TCP/IP Protocol
  • HTTP/HTTPS Protocol
  • Browser Rendering Pipeline
• Communication Protocols
  • HTTP/1.1, HTTP/2, HTTP/3
  • WebSocket Protocol
  • UDP vs TCP

API & Communication Tools

• REST APIs
  • RESTful Principles
  • HTTP Methods & Status Codes
  • API Versioning
  • Rate Limiting
• GraphQL
  • Queries & Mutations
  • Schema Design
  • Caching Strategies
  • Apollo Client vs Relay
• gRPC
  • Protocol Buffers
  • Streaming
  • Web gRPC
• Additional Patterns
  • JSON-RPC
  • SOAP (Legacy Systems)
  • WebRTC for Peer-to-Peer

---

2. Communication

Introduction

• Communication Overview
• Client-Server Architecture
• Bidirectional Communication

Techniques for Real-Time Data

• Short Polling
  • Use Cases
  • Pros & Cons
• Long Polling
  • Implementation
  • When to Use
• WebSockets
  • Full-Duplex Communication
  • Socket.io vs Native WebSocket
  • Reconnection Strategies
• Server-Sent Events (SSE)
  • EventSource API
  • Comparison with WebSockets
• WebHooks
  • Webhook Security
  • Retry Mechanisms
• Additional Techniques
  • WebRTC Data Channels
  • Message Queues (Frontend Integration)

---

3. Security

Introduction

• Security Overview
• Security Best Practices
• Security Mindset

Frontend Security Concepts

• Cross-Site Scripting (XSS)
  • Stored XSS
  • Reflected XSS
  • DOM-based XSS
  • Prevention Techniques
• iFrame Protection
  • X-Frame-Options
  • Frame Busting
  • Sandboxing
• Security Headers
  • Content-Security-Policy (CSP)
  • Strict-Transport-Security (HSTS)
  • X-Content-Type-Options
  • Referrer-Policy
• Client-side Security
  • JWT Storage Best Practices
  • Token Management
  • Secure Cookie Attributes
• Secure Communication (HTTPS)
  • TLS/SSL
  • Certificate Pinning
  • Mixed Content Issues
• Dependency Security
  • NPM Audit
  • Snyk & Dependabot
  • Supply Chain Attacks
• Compliance & Regulation
  • GDPR
  • CCPA
  • Cookie Consent
• Input Validation and Sanitization
  • DOMPurify
  • Validator Libraries
  • Schema Validation

Server-Side Security (Frontend Perspective)

• Server-Side Request Forgery (SSRF)
• Server-side JavaScript Injection (SSJI)
• SQL Injection (via APIs)
• Authentication & Authorization
  • OAuth 2.0 / OpenID Connect
  • Session Management
  • Multi-Factor Authentication (MFA)

Policy & Integrity

• Feature Policy | Permissions-Policy
• Subresource Integrity (SRI)
• Cross-Origin Resource Sharing (CORS)
  • Preflight Requests
  • Credential Handling
• Cross-Site Request Forgery (CSRF)
  • CSRF Tokens
  • SameSite Cookie Attribute
• Additional Security Topics
  • Clickjacking Prevention
  • Tabnabbing Protection
  • Prototype Pollution

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4. Testing

Introduction

• Testing Overview
• Testing Pyramid
• Testing Best Practices

Testing Techniques

• Unit & Integration Testing
  • Jest, Vitest, Mocha
  • Testing Library
  • Mocking & Stubbing
• End-to-End (E2E) & Automation Testing
  • Cypress
  • Playwright
  • Puppeteer
  • Selenium
• A/B Testing
  • Feature Flags
  • Split Testing
  • Analytics Integration
• Performance Testing
  • Lighthouse CI
  • WebPageTest
  • Load Testing
• Test-Driven Development (TDD) Overview
• Security Testing
  • OWASP ZAP
  • Penetration Testing
  • Vulnerability Scanning
• Additional Testing Types
  • Visual Regression Testing (Percy, Chromatic)
  • Accessibility Testing (axe-core)
  • Smoke Testing
  • Snapshot Testing
  • Contract Testing

Bonus

• Testing in React Components
  • Component Testing
  • Hook Testing
  • Context Testing

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5. Performance

Introduction

• Performance Overview
• Importance of Performance
• Core Web Vitals
  • Largest Contentful Paint (LCP)
  • First Input Delay (FID) / Interaction to Next Paint (INP)
  • Cumulative Layout Shift (CLS)

Monitoring & Tools

• Performance Monitoring
  • Real User Monitoring (RUM)
  • Synthetic Monitoring
  • Error Tracking (Sentry, Bugsnag)
• Performance Tools
  • Chrome DevTools
  • Lighthouse
  • WebPageTest
  • Performance API

Optimization Techniques

• Network Optimization
  • Resource Compression (Gzip, Brotli)
  • CDN Usage
  • HTTP/2 & HTTP/3
  • DNS Prefetching
  • Preconnect, Prefetch, Preload
  • Resource Hints
• Rendering Patterns
  • Client-Side Rendering (CSR)
  • Server-Side Rendering (SSR)
  • Static Site Generation (SSG)
  • Incremental Static Regeneration (ISR)
  • Streaming SSR
  • Progressive Hydration
  • Islands Architecture
• Build Optimization
  • Code Splitting
  • Tree Shaking
  • Bundle Analysis
  • Minification & Uglification
  • Dead Code Elimination
• Additional Optimization
  • Image Optimization (WebP, AVIF, Lazy Loading)
  • Font Optimization (FOUT, FOIT, Variable Fonts)
  • JavaScript Optimization (Defer, Async)
  • CSS Optimization (Critical CSS, Unused CSS Removal)
  • Virtual Scrolling
  • Web Workers
  • Request Batching & Debouncing

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6. Database & Caching

Introduction

• Database & Caching Overview
• Frontend Data Strategy

Frontend Storage Techniques

• Local Storage
  • Use Cases
  • Size Limits
  • Security Considerations
• Session Storage
• Cookie Storage
  • Cookie Attributes
  • Third-Party Cookies
• Indexed DB
  • Dexie.js
  • Complex Queries
• Additional Storage
  • Cache API
  • Web SQL (Deprecated but good to know)

Database Design

• Normalization
  • Normal Forms
  • Denormalization for Frontend
• Data Modeling
  • Entity Relationships
  • Schema Design for Frontend Consumption
• Query Optimization

Caching Techniques

• HTTP Caching
  • Cache-Control Headers
  • ETag & Last-Modified
  • Stale-While-Revalidate
• Service Worker Caching
  • Cache Strategies (Network First, Cache First, etc.)
  • Background Sync
• API Caching
  • Client-Side Caching
  • SWR (Stale-While-Revalidate)
  • React Query / TanStack Query
• Additional Caching
  • Memoization
  • Edge Caching (CDN)
  • Browser Cache vs Application Cache

State Management

• Managing Application State
  • Redux / Redux Toolkit
  • Zustand
  • MobX
  • Recoil
  • Jotai
  • Context API
  • State Machines (XState)
• Server State vs Client State
• Optimistic Updates
• State Persistence

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7. Logging & Monitoring

Introduction

• Logging & Monitoring Overview
• Observability Pillars

Core Concepts

• Telemetry
  • Metrics Collection
  • Distributed Tracing
  • User Session Recording
• Alerting
  • Error Boundaries
  • Notification Systems
  • Incident Management
• Fixing Issues
  • Debugging Techniques
  • Source Maps
  • Reproduction Steps
• Additional Concepts
  • Log Aggregation (LogRocket, Datadog)
  • Application Performance Monitoring (APM)
  • Analytics (Google Analytics, Mixpanel, Amplitude)
  • Feature Usage Tracking
  • Crash Reporting

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8. Accessibility

Accessibility Overview

• WCAG Guidelines
• ARIA (Accessible Rich Internet Applications)
• Semantic HTML

Keyboard Accessibility

• Tab Navigation
• Keyboard Shortcuts
• Focus Indicators

Screen Reader Compatibility

• ARIA Labels & Descriptions
• Live Regions
• Screen Reader Testing

Focus Management

• Focus Trapping
• Skip Links
• Focus Order

Color Contrast

• WCAG Contrast Ratios
• Color Blindness Considerations

Accessibility Tools

• axe DevTools
• WAVE
• Lighthouse Accessibility Audit
• Screen Readers (NVDA, JAWS, VoiceOver)

Fixing Accessibility Issues

• Common Violations
• Remediation Strategies

Additional Topics

• Mobile Accessibility
• Forms Accessibility
• Alternative Text for Images
• Captions & Transcripts
• Accessible Animations (prefers-reduced-motion)

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9. Offline Support

Service Workers

• Service Worker Lifecycle
• Caching Strategies
• Background Sync
• Push Notifications

Progressive Web Applications (PWAs)

• Web App Manifest
• Install Prompts
• App Shell Architecture
• Offline First Strategy
• Workbox

Additional Offline Features

• IndexedDB for Offline Data
• Network Detection
• Offline UI Patterns
• Sync Conflicts Resolution

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10. Low-Level Design (LLD)

Component Patterns

• Component Design
  • Atomic Design
  • Compound Components
  • Render Props
  • Higher-Order Components (HOC)
• Design Systems
  • Component Libraries
  • Theming
  • Token Systems

UI Patterns & Features

• Config-Driven UI
• Shimmer UI / Skeleton Screens
• Routing & Protected Routes
  • React Router / Next.js Router
  • Route Guards
  • Dynamic Routes
• State Management + Libraries
• Multi-Language Support (i18n)
  • react-i18next
  • FormatJS
  • RTL Support
• Infinite Scroll
  • Virtual Scrolling
  • Intersection Observer
• Accordion
• Reddit Nested Comments
  • Recursive Components
• Image Slider / Carousel
• Pagination (Part 1 & Part 2)
  • Cursor-based
  • Offset-based
• Real-Time Updates
• YouTube Live Stream Chat UI
• Autocomplete & Search Bar
  • Debouncing
  • Fuzzy Search
  • Highlighting

Additional LLD Topics

• Modal & Dialog Management
• Toast Notifications
• Dropdown & Select Components
• Tabs Component
• Form Handling & Validation
  • React Hook Form
  • Formik
  • Yup / Zod Validation
• Drag and Drop
• File Upload
  • Progress Indicators
  • Chunk Upload
• Data Tables
  • Sorting, Filtering, Search
  • TanStack Table
• Charts & Graphs
• Date/Time Pickers
• Rich Text Editors
• Command Palette
• Virtualized Lists
• Responsive Design Patterns

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11. High-Level Design (HLD)

HLD Overview

• System Design Fundamentals
• Scalability Principles
• Architecture Patterns
• Trade-offs & Decisions

Applications & Architectures

Social Media & Content

• Photo Sharing App (Instagram)
  • Image Upload & Optimization
  • Feed Generation
  • Story Feature
  • Like/Comment System
• News Media Feed (Facebook/Twitter)
  • Timeline Architecture
  • Real-time Updates
  • Recommendation Engine
  • Content Moderation

E-commerce

• E-commerce App (Amazon/Flipkart)
  • Product Catalog
  • Search & Filtering
  • Shopping Cart
  • Payment Integration
  • Order Tracking
  • Recommendation Engine

Streaming

• Video Streaming (Netflix)
  • Adaptive Bitrate Streaming
  • CDN Strategy
  • Recommendation Algorithm
  • Content Delivery
  • Offline Downloads
• Music Streaming (Spotify)
  • Audio Streaming
  • Playlist Management
  • Collaborative Playlists
  • Discovery Algorithm

Productivity & Communication

• Email Client (Gmail/Outlook)
  • Email Threading
  • Search Functionality
  • Offline Support
  • Attachment Handling
  • Spam Filtering
• Google Docs & Google Sheets
  • Operational Transformation (OT)
  • Conflict-Free Replicated Data Types (CRDTs)
  • Real-time Collaboration
  • Cursor Positioning
  • Undo/Redo

Tools & Utilities

• Diagram Tools (Excalidraw)
  • Canvas Rendering
  • Collaborative Drawing
  • Export Functionality
• Analytics Dashboard (Google Analytics)
  • Data Visualization
  • Real-time Metrics
  • Report Generation
  • Data Aggregation

Real-time Applications

• Live Commentary (CricInfo/Crickbuzz)
  • Live Score Updates
  • Ball-by-Ball Commentary
  • Real-time Notifications
  • WebSocket Implementation

Microfrontend Architecture

• Module Federation
• Single-SPA
• Micro-app Communication
• Shared Dependencies
• Independent Deployment
• Team Boundaries

Additional HLD Topics

• Chat Application (WhatsApp/Slack)
  • Message Queue
  • Read Receipts
  • End-to-End Encryption
  • Group Chats
• Video Conferencing (Zoom/Meet)
  • WebRTC
  • Peer-to-Peer vs Server-Mediated
  • Screen Sharing
• Ride-Sharing App (Uber/Lyft)
  • Real-time Location Tracking
  • Map Integration
  • Matching Algorithm
• Food Delivery App (DoorDash/Zomato)
  • Restaurant Search
  • Order Management
  • Real-time Tracking
• Booking System (Airbnb/Booking.com)
  • Search & Filters
  • Availability Calendar
  • Booking Conflicts
• Content Management System (CMS)
  • WYSIWYG Editor
  • Version Control
  • Publishing Workflow
• Notification System
  • Push Notifications
  • In-app Notifications
  • Email Notifications

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12. Modern Frontend Architecture

Build Tools & Bundlers

• Webpack
• Vite
• Rollup
• Turbopack
• esbuild
• SWC

Meta Frameworks

• Next.js
  • App Router
  • Server Components
  • Server Actions
• Remix
• Astro
• SvelteKit
• Nuxt.js

Design Patterns

• SOLID Principles in Frontend
• MVC, MVVM, MVP
• Flux Architecture
• Repository Pattern
• Facade Pattern
• Observer Pattern
• Singleton Pattern

Code Quality

• Linting (ESLint)
• Formatting (Prettier)
• Type Safety (TypeScript)
• Code Reviews
• Documentation (Storybook, JSDoc)
• Git Workflow & Version Control

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13. DevOps & Deployment

CI/CD

• GitHub Actions
• GitLab CI
• Jenkins
• CircleCI

Deployment Strategies

• Blue-Green Deployment
• Canary Deployment
• Rolling Updates
• Feature Toggles

Hosting & Infrastructure

• Vercel
• Netlify
• AWS (S3, CloudFront, Amplify)
• Google Cloud Platform
• Azure
• Docker Containers

Monitoring & Analytics

• Performance Monitoring in Production
• Error Tracking
• Usage Analytics
• A/B Testing Infrastructure

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14. Advanced Topics

Web Assembly (WASM)

• Performance-Critical Operations
• Porting C/C++ Code
• Use Cases

Edge Computing

• Edge Functions
• Cloudflare Workers
• Vercel Edge Functions

AI/ML Integration

• TensorFlow.js
• ML Models in Browser
• AI-Powered Features

Browser APIs

• Web Bluetooth
• Web USB
• Web NFC
• Media Capture & Streams
• Web Audio API
• Canvas & WebGL
• Geolocation API
• Battery Status API
• Vibration API

Emerging Technologies

• Web3 Integration
• Blockchain Frontend
• WebGPU
• WebXR (AR/VR)

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15. Soft Skills & Career

Technical Communication

• Technical Writing
• Documentation
• Code Comments
• Architecture Decision Records (ADRs)

Collaboration

• Agile/Scrum
• Code Reviews
• Pair Programming
• Cross-functional Teams

Problem Solving

• Debugging Strategies
• Root Cause Analysis
• Performance Profiling
• Trade-off Analysis

Continuous Learning

• Staying Updated
• Open Source Contribution
• Technical Blogs
• Conference Talks

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Appendix: Resources

Books

• "Designing Data-Intensive Applications" by Martin Kleppmann
• "Web Performance in Action" by Jeremy Wagner
• "High Performance Browser Networking" by Ilya Grigorik

Online Platforms

• Frontend Masters
• Web.dev
• MDN Web Docs
• JavaScript.info

Practice Platforms

• Frontend Interview Handbook
• GreatFrontEnd
• LeetCode Frontend Questions
• Building Real-World Projects

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Study Approach

1. Foundation First: Master networking, communication, and security basics
2. Hands-On Practice: Build projects implementing each LLD pattern
3. Progressive Complexity: Move from LLD to HLD gradually
4. Real-World Projects: Clone popular applications
5. Performance Focus: Always optimize and measure
6. Security Mindset: Think about security in every design decision
7. Continuous Testing: Write tests alongside features
8. Document Learning: Maintain a knowledge base

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This roadmap is comprehensive but not exhaustive. Frontend system design is constantly evolving, so stay curious and keep learning!