Building JSON APIs

Most Node backends expose JSON REST APIs for SPAs and mobile apps—predictable URLs, HTTP verbs, and structured error payloads.

CRUD sketch

• GET /api/items — list
• GET /api/items/:id — detail
• POST /api/items — create (201 + Location header)
• PATCH /api/items/:id — partial update
• DELETE /api/items/:id — remove (204)

Error shape

res.status(400).json({
  error: 'Validation failed',
  fields: { email: 'Invalid format' }
});

Versioning

Prefix routes (/api/v1/...) or use Accept headers—pick one team convention and document breaking changes.

Important interview questions and answers

1. Q: REST vs GraphQL?
   A: REST uses multiple endpoints; GraphQL one endpoint with client-specified fields—Node supports both (Apollo, Mercurius).
2. Q: Idempotent methods?
   A: GET, PUT, DELETE should be safe/repeatable; POST creates new resources—important for retries.

Self-check

1. Which status code for successful create?
2. Why return structured validation errors?

Tip: Always set Content-Type: application/json and use JSON.stringify—never concatenate user input into JSON strings manually.