Question 1

How do I add a new API route to an Express server without bloating routes.ts?

Accepted Answer

Create or extend a domain router in routes/domains/<domain>.ts with the handler and validation, then mount that router in routes.ts. Keep persistence logic in a matching repositories/ file rather than inline in the route.

Question 2

Where should new database query code live in a layered Node.js backend?

Accepted Answer

New persistence logic belongs in repositories/ as plain TypeScript functions using db or tx handles. Do not add new methods to the legacy storage.ts facade; it should only delegate to repositories.

Question 3

How do I migrate logic out of a legacy storage.ts facade?

Accepted Answer

Extract the logic into the appropriate repositories/ file, then update storage.ts to delegate to the repository so existing callsites keep working. The goal is to shrink the storage.ts surface over time until it can be removed.

Question 4

When should Express middleware not be placed inside route files?

Accepted Answer

Express middleware such as request ID correlation or metrics collection belongs in a dedicated middleware/ directory, not inside routes.ts or domain router files. Domain files should contain only handlers, validation, and service calls.

Question 5

What are the limitations of a composition root pattern for large Express apps?

Accepted Answer

The composition root centralizes router mounting, so it grows as domains are added and requires discipline to keep free of inline handlers. Teams must enforce the boundary with review checklists and structural tests to prevent logic from drifting back in.

server-domain-architecture

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