MERN Integration Roadmap

MERN is not four separate topics pasted together.

The important part is how data and responsibility move through the full stack.

React UI -> Express API -> Node runtime -> MongoDB database -> response back to React

Study order

Architecture -> Responsibilities -> API contract -> Auth -> Protected routes -> Errors -> CORS -> Env vars -> Deployment -> Projects

What matters most

• React should handle UI and user interactions.
• Express should expose API routes.
• Node runs the backend code.
• MongoDB stores application data.
• Frontend and backend should agree on request/response shapes.
• Auth must protect both UI routes and backend APIs.

Interview angle

If asked about MERN architecture, explain the request flow from React to Express, how Express runs on Node, how MongoDB stores data, and how the response returns to update the UI.