Backend basics

backend-basics

Build someone's first backend: a small API they wrote, deployed on a current no-card plan, answering requests from their own frontend. The point is to make "server" concrete. Code that runs on a machine that is always on, holds secrets the browser can't see, and answers HTTP requests.

Ground rules

• The backend must serve a real need from their existing project: hiding an API key, sharing data between visitors, or doing work the browser can't. If nothing exists yet, run build-web-app first, or build the frontend and backend as one small pair.
• Compare current official plan and runtime documentation before choosing a host. Serverless functions or a small Node server are both reasonable. Record the limits and what happens at the edge of them, including request caps, sleeping instances, and retention. No card details anywhere; if a supposedly free host demands a card, pick another host.
• Their accounts, their keys. They sign up themselves; secrets go in the host's env-var settings and a local .env that is gitignored before it is created. git status proves it.
• Two or three endpoints, no more. A backend that does one job completely beats a scaffold with ten empty routes.
• They run every deploy and every curl. You narrate what each command does in one line first.

The path

1. Say the shape out loud together: browser calls your API, your API does the private work, JSON comes back. Draw it as three boxes if that helps. Then pick the two endpoints this project needs.
2. Hello endpoint, locally: one route returning JSON. Hit it with curl and with the browser so both feel the same.
3. Deploy that hello endpoint before writing anything else. Free tiers make this a ten-minute step; a live URL early keeps the rest honest.
4. Real endpoints: the private fetch with the hidden key, or the shared read/write the project needs. Env vars set in the host dashboard by them, mirrored in local .env.
5. Wire the frontend to it with fetch. Handle CORS when it bites (it will) and explain in two sentences why the browser blocked the call.
6. Unhappy paths: bad input gets a 400 with a message, a down upstream gets caught, and they test both with curl.

Done

• A deployed API at a URL, written by them, with 2 to 3 endpoints
• Their frontend calling it and rendering the result
• Secrets only in host env vars and a gitignored .env; nothing secret in the repo or the browser dev tools
• They can trace one request from click to response out loud

Then: database-basics when the API needs memory that survives a redeploy, or auth-basics when different users should see different things.