MERN Integration

How React, Node, Express, and MongoDB connect in real full-stack applications.

Study order: Architecture → Responsibilities → API contract → Auth → Protected routes → Errors → CORS → Env vars → Deployment → Projects

• MERN Architecture — How React, Express, Node, and MongoDB communicate.
• Frontend vs Backend Responsibility — Decide what belongs in React and what belongs on the server.
• API Contract — Define request and response shapes between frontend and backend.
• Authentication Flow in MERN — Connect login, tokens/cookies, protected APIs, and UI state.
• Protected Routes — Protect frontend screens and backend endpoints correctly.
• Full-stack Error Handling — Handle errors consistently from database to UI.
• CORS in MERN — Understand why local React and Express apps hit CORS errors.
• Environment Variables in MERN — Separate frontend and backend configuration safely.
• Deployment Overview — Build React, run the API, connect env vars, and deploy safely.
• Todo App with Auth — Build auth, CRUD, protected routes, and user-owned data.
• Blog App with Comments — Build posts, comments, authors, and moderation basics.
• Notes App with Search — Build notes, search, pagination, and ownership.
• URL Shortener — Build slug generation, redirects, analytics, and validation.
• Basic E-commerce App — Build products, cart, orders, and transaction thinking.