Node.js

Why Node scales connections cheaply on one thread - and what CPU-bound work does to it.

import vs require, package.json 'type' and interop - the module system you'll debug eventually.

Dependencies, lockfiles, semver and npx - the contract of every Node project.

fs, path, http, os and events - the standard library that pays rent daily.

Processing data bigger than memory: readable/writable streams, piping and backpressure at concept level.

Routing, middleware chains and centralised error handling - the request pipeline as one coherent design.

Resources, verbs, status codes and pagination - APIs a stranger can navigate without a meeting.

Fastify for speed, NestJS for structure, Hono for the edge - Express concepts transfer; know when each alternative earns its keep.

Schema-validating every input at the boundary (zod/joi) - the cheapest security and quality win.

bcrypt hashing, token vs session trade-offs, refresh flows and protected routes.

CORS, rate limiting, helmet headers and injection defence - the OWASP basics wired into middleware.

Postgres with pooling, parameterised queries and transactions - or Prisma when an ORM earns its keep.

Mongoose schemas, queries and aggregation - document modelling with guardrails.

Vitest/Jest + supertest: unit tests for logic, integration tests for endpoints - confidence to refactor.

env vars, secrets and twelve-factor structure - one build, many environments.

The observer pattern at Node's core - how streams, servers and your own decoupled modules communicate.

Shelling out, spawning workers and clustering - escaping the single thread for CPU-bound work.

argv parsing (commander), prompts (inquirer) and exit codes - Node as a tool-building platform, not just a server.

package.json exports, semver discipline and npm publish - shipping reusable code to the registry.

--inspect with DevTools, heap snapshots and spotting leaks - evidence-driven debugging under load.

Central error middleware, structured logs (pino) and not leaking stack traces to clients.

Docker or a PaaS, health checks, graceful shutdown and process managers.

Profiling, avoiding event-loop blocking, and caching hot reads - measured, not guessed.

Take the OneRoadmap Node.js certification - verified backend fundamentals.