Master Table of Contents

• See full index in [01. Introduction]

Who this chapter is for

• Frontend learners who want practical full-stack fundamentals
• Beginners building their first backend API with TypeScript
• Anyone who wants better frontend-backend collaboration in real projects

What you’ll learn

• Node.js server fundamentals with an API-first mindset
• REST API design basics that are easy to maintain
• Request validation and consistent error response patterns

Why this topic matters

When you understand backend basics, you stop treating APIs like black boxes.

This helps you design better frontend integrations, debug faster, and communicate much better with backend teammates.

Core concepts

HTTP fundamentals

• Methods: GET, POST, PUT/PATCH, DELETE
• Status codes and response shape consistency

Think of HTTP as contract language between client and server.

API architecture

• Routes, controllers, services (basic separation)
• Validation before processing data

Simple separation keeps code readable as endpoints grow.

Step-by-step walkthrough

Step 1 — Create API project

Initialize a Node + TypeScript project with a clean folder structure.

Step 2 — Add CRUD routes

Implement CRUD endpoints with consistent response shape.

Step 3 — Add validation and error middleware

Add validation and centralized error middleware so responses stay predictable.

Goal: API behavior is clear for both frontend and backend developers.

Practical examples

Example 1 — GET route

app.get("/tasks", (_req, res) => {
	res.json([{ id: 1, title: "Learn Node.js" }]);
});

Tip:

• Keep route handlers short; delegate heavy logic to service functions.

Example 2 — Validation rule concept

• Ensure title is non-empty
• Return 400 with readable message if invalid

Also keep error shape consistent (for example: message, code, and optional details).

Common mistakes and how to avoid them

• Returning inconsistent JSON structures -> define and follow one response standard
• Skipping input validation -> invalid data leaks into storage
• Putting business logic directly in routes -> keep handlers slim and move logic to services
• Exposing internal error details -> map to safe client-facing messages

Mini Project

• Build a Task API with:
• full CRUD endpoints,
• request body validation,
• consistent success/error response format,
• in-memory storage for simplicity.

Bonus:

• Add pagination query params for the task list endpoint.

Quick practice

• Add one GET route and one POST route
• Return 400 for invalid body
• Add one simple in-memory data store
• Add one reusable helper for API success responses

Key takeaways

• Backend basics make frontend developers much stronger in real product teams
• Consistent API contracts reduce integration bugs significantly
• Validation and clear error standards are non-negotiable for reliable APIs

Next step

Continue to [18. Deployment and Production Basics].