Week 1 — Node.js, Express & NestJS HTTP foundations

Understand the Node runtime and Express request flow before learning the structure Nest adds — then ship Notes P1 as this week’s mini-project.

1. Node.js runtime, modules & npm
Nest and Express both run inside Node, so runtime, module, package, and environment behavior still matters after a framework is added.
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2. Node.js async work & the event loop
HTTP handlers, database calls, password hashing, and file operations are asynchronous. Understanding await, rejection, and blocking work prevents framework code from hiding runtime-level failures.
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3. Express routing, middleware & errors
Nest uses Express (or Fastify) as its HTTP platform adapter. Learn the raw request flow first so Nest modules, guards, and pipes map to something concrete.
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4. Nest architecture & CLI
After Node and Express, map what Nest adds: modules, DI, decorators, and the CLI that scaffolds them. Nest ≠ Next — Nest is an HTTP API and database owner, while a React/Next frontend is a client that calls it over HTTP.
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5. Modules
Every Nest feature — tickets, auth, health — is a module. AppModule is the root module that assembles the whole app. Understand modules before controllers; they tell you what exists.
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6. Dependency injection
DI is the hardest Nest concept to fake your way through. Intermediate engineers must reason about tokens, module visibility, scope, and circular graphs — not only “put it in the constructor.”
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7. Decorators
Nest is built almost entirely from decorator metadata: which class is a controller, which method handles which route, which parameter is public/role-gated. A Nest app commonly defines its own decorators for auth.
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8. Controllers
Controllers are the HTTP front door of every Nest module. Keep them thin — parsing, delegating, responding — never doing business logic or raw SQL themselves.
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9. Services
TicketsService is a clear example: repository injection, a DTO in, a mapped response out, and NotFoundException for missing records.
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10. Request pipeline (middleware → guards → pipes → handler → filters)
This is the single most useful Nest debugging model. Intermediate engineers do not guess — they map a status code to a pipeline stage and open the right file.
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11. REST API + Postman / curl
Hands-on API practice for the week: hit /health, walk authenticated CRUD routes, and read ValidationPipe / filter errors.
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12. Notes API — Nest HTTP milestone
Locks Week 1 Node/Express + Nest HTTP foundations. Use a controller→service→DTO CRUD slice as your worked example.
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End-of-week mini-project · practice only

Link Shortener API (Nest HTTP, in-memory)

Build a URL shortener with Nest: create short codes, redirect visitors, and count hits — all in memory, no database yet.

Definition

A standalone Nest HTTP service that turns long URLs into short codes and 302-redirects visitors, exercising the full Week 1 request pipeline without any persistence.

In simpler words

Make your own tiny bit.ly. You POST a long URL, get a short code back, and hitting the code redirects you while the service counts clicks.

Concepts covered this week

Node.js runtime, modules & npm: Scaffold with the Nest CLI; wire npm scripts (start:dev, build) and read package.json.
Async work & the event loop: A non-blocking setInterval sweep expires old links without freezing request handling.
Express routing, middleware & errors: Warm up with a 15-line Express version of the redirect route, then rebuild it the Nest way.
Nest architecture & CLI: nest g module/controller/service generates the LinksModule slice.
Modules: LinksModule groups the controller + providers and is imported by AppModule.
Dependency injection: Inject LinksService and a CodeGenerator provider through the constructor.
Decorators: @Module, @Controller, @Injectable, @Get/@Post, @Param, @Body describe the wiring.
Controllers: LinksController maps POST /links, GET /:code, and the JSON admin routes.
Services: LinksService holds the in-memory Map and all create/lookup/stats logic.
Request pipeline: A logger middleware, an ApiKeyGuard, a ValidationPipe, and a NotFound filter run in order.
REST API + Postman / curl: Exercise every route from Postman/curl and confirm status codes (201, 302, 404).

Deliverables

LinksModule + LinksController + LinksService generated via the Nest CLI
POST /links (validated body) returning a unique short code; GET /:code issuing a 302 redirect
GET /api/links (list) and GET /api/links/:code/stats (hit count)
A request-logger middleware, an ApiKeyGuard on admin routes, a global ValidationPipe, and a filter that returns clean 404 JSON

Build guide

Scaffold the projectRun nest new link-shortener, then nest g module/controller/service links. Enable a global ValidationPipe in main.ts.
Contrast with raw ExpressWrite a throwaway Express route that redirects /:code so you feel what Nest abstracts (routing, middleware order, error handling).
Model the data in memoryIn LinksService keep a Map<string, { url; hits; createdAt }>. Add a CodeGenerator provider returning a short base62 id.
Create + validateCreateLinkDto with @IsUrl(); POST /links returns 201 with { code, shortUrl }. Reject unknown fields with whitelist/forbidNonWhitelisted.
Redirect + countGET /:code looks up the map, increments hits, and 302-redirects to the original URL; unknown codes throw NotFoundException.
Protect admin routesAdd an ApiKeyGuard reading an x-api-key header and apply it to the list/stats routes to practice guards.
Expire in the backgroundUse setInterval in onModuleInit to sweep links older than N minutes — non-blocking event-loop work.
Test the whole surfaceDrive create → redirect → stats → list → 404 from Postman/curl and verify each status code.

Acceptance checklist

- [ ] Nest CLI scaffold with LinksModule/Controller/Service
- [ ] POST /links validates the body and returns a unique code
- [ ] GET /:code redirects (302) and increments the hit counter
- [ ] Unknown code returns a clean 404 via an exception filter
- [ ] Admin routes protected by a guard; logger middleware runs first
- [ ] Every route verified from Postman/curl

Stretch goals

Add custom aliases (POST a desired code) and reject collisions with 409.
Return a QR-code image for a short link.
Hide the in-memory Map behind an interface so Week 2 can drop in Postgres.

Tips

Keep the store behind a service boundary — Week 2 will replace the Map with a repository.
Redirect status is 302 (or 301 for permanent); return JSON only on the /api routes.