# ADR 0001: Backend Framework — Express.js

**Date:** 2026-04-26
**Status:** Accepted

## Context

The backend serves a JSON REST API consumed by the Angular frontend. The requirements are straightforward: HTTP routing, middleware chaining, JSON body parsing, JWT authentication, and database access. No server-side rendering, no real-time features, no heavy framework conventions are needed.

## Decision

Use Express.js as the HTTP framework. The application is structured around:
- `src/routes/api/<domain>/` — route definitions by functional domain
- `src/controllers/` — request/response handling
- `src/services/` — business logic
- `src/middlewares/` — cross-cutting concerns (auth, error handling, async wrapper)
- `createApp.js` — application factory (separates app creation from server startup, enabling testability)

## Consequences

- **Positive:** Minimal abstraction. Full control over middleware order and request lifecycle.
- **Positive:** Large ecosystem. Well-understood by the team.
- **Negative:** No convention over configuration — project structure is manually maintained.
- **Negative:** Async error handling requires explicit wrapping (`asyncHandler` middleware) since Express 4 does not catch promise rejections natively. Express 5 (not yet used) handles this automatically.