Core Code
Core Code Modern Dev Handbook
REACT Contents
React Fundamentals
React Architecture Overview JSX and Rendering Model Component Design Principles Props and Data Flow State Management with useState Side Effects with useEffect Event Handling Patterns Conditional Rendering Strategies Lists, Keys, and Reconciliation Forms and Controlled Components Component Composition Lifting State and Shared State Basic Routing with React Router Failure Modes in Beginner React Apps
React + TypeScript
Typing Functional Components Typing Props and Children useState and Type Inference useReducer with Type Safety Typing Event Handlers Generic Components Utility Types in React Discriminated Unions for UI State Strict Mode and Null Safety API Response Typing Strategies Form Typing Patterns Avoiding any and Unsafe Casts Type-Safe Context API Failure Modes in React + TypeScript
React Advanced Patterns
Custom Hooks Architecture Context vs Prop Drilling Tradeoffs Compound Components Pattern Controlled vs Uncontrolled Abstractions Render Props and Pattern Alternatives State Machines in React Performance Optimization Playbook Memoization Strategies Code Splitting and Lazy Loading Error Boundaries and Recovery Portal Architecture Large Scale Folder Structure Testing Strategy: Unit and Integration Common React Anti Patterns
React Production
CSR vs SSR vs SSG Hydration and Mismatch Failures Next.js Architecture Overview App Router Deep Dive Authentication Patterns Token Storage Security Role Based UI Control API Integration Patterns Rate Limiting and UI Resilience Frontend Security Checklist XSS in Modern React Observability in Frontend Bundle Optimization Production Incident Playbook
Distributed Systems
Distributed System Fundamentals CAP Theorem in Practice Consistency Models Replication Strategies Leader Election Concepts Consensus Algorithms Overview Event Driven Architectures Message Queues and Delivery Guarantees Idempotency Patterns Saga Pattern Circuit Breakers Backpressure and Flow Control Observability in Distributed Systems Failure Scenarios and Postmortems

Frontend Security Checklist

Use this production checklist to reduce client side risk. Covers XSS controls, token handling, CSP, dependency hygiene, clickjacking, supply chain defenses, and incident ready logging practices.
On this page

Threat Model for Frontend

  • Primary risks: XSS, token theft, session fixation, CSRF for cookie sessions, supply chain compromise.
  • UI enforcement is not security. Server enforces authorization and validation.
  • Production rule: minimize secrets and trust boundaries in the client.

Input and Output Safety

  • Never render untrusted HTML. Avoid unsafe HTML injection APIs.
  • Escape untrusted text by default, keep it as text, not markup.
  • Sanitize only when HTML is required and document the allowed subset.

Authentication and Tokens

  • Prefer HttpOnly Secure SameSite cookies for session tokens.
  • If bearer tokens exist, keep them in memory and rotate frequently.
  • Implement logout as server revocation plus client cleanup.

Network Controls

  • Use HTTPS everywhere and enforce HSTS at the edge.
  • Use CORS narrowly, never wildcard with credentials.
  • Do not expose internal endpoints and debug routes in production builds.

Content Security Policy

  • Deploy CSP to reduce XSS impact.
  • Avoid unsafe-inline and unsafe-eval in production.
  • Use nonces or hashes for required inline scripts.

Clickjacking and UI Redress

  • Prevent framing with frame-ancestors in CSP or X-Frame-Options where applicable.
  • Protect sensitive actions with explicit confirmations when required.

Dependencies and Supply Chain

  • Lock dependencies and use automated vulnerability scanning.
  • Review packages with high risk profiles and avoid unmaintained libraries.
  • Build and deploy from trusted CI with signed artifacts where possible.

Operational Logging

  • Log auth events: login, logout, refresh failures, permission changes.
  • Log security relevant errors with build version and route context.
  • Do not log secrets, tokens, or PII into client logs.

Release Gate Checklist

  • No unsafe HTML injection paths without sanitization and tests.
  • Token storage policy documented and enforced.
  • CSP deployed and monitored for violations.
  • Dependency audit passes and lockfile is stable.
  • Frame protections are enabled.
  • Security logs are wired to monitoring without sensitive data.
XSS in Modern React →