Route requests and return JSON

Bun can match routes before calling the fallback fetch handler.

Let’s create two read-only routes:

type Note = {
  id: number
  title: string
}

const notes: Note[] = [
  { id: 1, title: 'Learn Bun' },
  { id: 2, title: 'Build the notes API' },
]

const server = Bun.serve({
  routes: {
    '/api/notes': {
      GET: () => Response.json(notes),
    },
    '/api/notes/:id': request => {
      const id = Number(request.params.id)
      const note = notes.find(note => note.id === id)

      if (!note) {
        return Response.json(
          { error: 'Note not found' },
          { status: 404 },
        )
      }

      return Response.json(note)
    },
  },
  fetch() {
    return Response.json(
      { error: 'Route not found' },
      { status: 404 },
    )
  },
})

console.log(`Listening on ${server.url}`)

The :id segment creates request.params.id. It is a string, so we convert it before comparing it with numeric IDs.

Try the collection route:

curl http://localhost:3000/api/notes

Then request one note:

curl http://localhost:3000/api/notes/1

An unknown ID returns JSON with status 404. An unmatched path reaches fetch() and returns a different 404 response.

HTTP status codes are part of the API contract. Do not return 200 for every outcome and ask clients to inspect an error string.