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

Conditional Rendering Strategies

Conditional rendering must be deterministic. Model UI states explicitly (loading/empty/error/ready) and avoid boolean soup that produces impossible combinations and flicker.
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Why Conditional Rendering Fails in Production

  • Most UIs have multiple states: loading, error, empty, ready, partial.
  • Ad-hoc booleans create contradictions (e.g., loading + error + data).
  • Inconsistent transitions cause flicker and confusing user feedback.

State Enumeration (Baseline)

  • loading: request in-flight, no usable data.
  • error: request failed, show actionable retry.
  • empty: request succeeded but no results.
  • ready: data is available and valid.

Preferred Pattern: Early Returns

function UsersView({ state }) {
  if (state.status === 'loading') return <Spinner />;
  if (state.status === 'error') return <ErrorBox message={state.message} />;
  if (state.status === 'empty') return <EmptyState />;
  return <UserTable users={state.users} />;
}

Avoid Boolean Soup

// ❌ Hard to reason about, easy to contradict
if (isLoading) ...
if (hasError) ...
if (data) ...
if (!data) ...

// ✅ Use a single state machine-like status
// status: loading | error | empty | ready

Operational Checklist

  • Every async view has explicit loading, error, empty, ready UI.
  • Error UI includes a retry action and preserves context.
  • Loading UI is stable (no layout jumps if possible).
  • Transitions are intentional (don't clear data unless required).

Failure Modes

  • Flicker: clearing data on refetch causes empty → loading → ready flashes.
  • Silent failure: error state hidden by a falsey condition.
  • Impossible combinations: multiple booleans true at once.
  • Retry loops: auto-retry without caps or user control.

Incident Triage Playbook

  • Step 1: Confirm state model (is it enumerated or boolean soup?).
  • Step 2: Verify transitions on refetch (keep previous data or not?).
  • Step 3: Ensure error UI is reachable and actionable.
  • Step 4: Add logging around state transitions to prove the sequence.

Code Review Checklist

  • No nested ternary chains for major view states.
  • Error and empty states are explicitly handled.
  • State transitions are deterministic and testable.
Lists, Keys, and Reconciliation →