01 — Why Express

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Goal: understand why a CLI todo needs to become a web API and why Express is the right tool for the job.

What the CLI does well

The CLI todo works fine for one person on one machine:

node cli.js add "buy milk"
node cli.js list

But it has hard limits:

Limit	Why it matters
Single user	Only the person at the terminal can use it
No persistence contract	The JSON file lives on one filesystem — no sharing
No access control	Anyone who can run the file can edit todos
No remote access	You can't use it from your phone, another laptop, or a web app

What a web API gives you

A web server exposes the same logic over HTTP. Any client — web app, mobile app, curl, another server — can call it:

GET  /api/todos      → list all todos
POST /api/todos      → create a todo
PATCH /api/todos/1   → mark done
DELETE /api/todos/1  → remove a todo

Why Express

Express is the most popular Node.js web framework:

• Minimal — a few lines to handle a request
• Middleware ecosystem — auth, logging, rate limiting as plugins
• Stable — v4 has been production-tested for a decade
• Zero config — no CLI boilerplate, just npm install express

The stack you'll build

Layer	Technology
HTTP server	Express
Database	PostgreSQL via pg
Auth	bcrypt + jsonwebtoken
Container	Docker + docker-compose
CI/CD	GitHub Actions
Tests	Jest + supertest

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