getHeaders()

Every method on a client has getHeaders(), which returns the headers its endpoint sends from configuration. Look here when you want to check those headers, in a test or while debugging, without making a call.

It returns a Record<string, string>: the client’s headers merged with the endpoint’s, with the endpoint’s winning, and every name in lowercase.

import { createApi, defineRequest } from 'liaise'

const api = createApi({
  baseUrl: 'https://api.example.com',
  headers: { 'X-Api-Version': '1', 'X-Client': 'web' },
  requests: {
    getUser: defineRequest<{ id: string }>()({
      method: 'GET',
      path: '/users/:id',
      headers: { 'X-Api-Version': '2' },
    }),
  },
})

api.getUser.getHeaders() // { 'x-api-version': '2', 'x-client': 'web' }

• It leaves out per-call headers, headers a middleware sets, and the Content-Type liaise picks from the body. Those exist only once a call happens.
• It returns a new plain object each time. Changing it changes nothing.
• An invalid configured header gives {}. A value with a character outside Latin-1, or a name with a space, would make a Headers object throw, and getHeaders() never throws.
• GraphQL operations have it too, including graphql.query.getCategory.getHeaders() and graphql.mutation.updateCategory.getHeaders() on a client split into queries and mutations.

Next: withHeaders() makes a copy of a client with more headers.