Construct URLs, headers, and bodies

Prerequisites

Run the local server and use the ESM TypeScript setup from your first request. Replace its client call with the following complete request; the fixture accepts exactly /users/1, without query parameters.

Address a resource

import { Fetcher, ResultExtractors } from '@ahoo-wang/fetcher';

const api = new Fetcher({ baseURL: 'http://127.0.0.1:8787' });
const user = await api.get<{ id: number; name: string }>(
  '/users/{id}',
  {
    urlParams: { path: { id: 1 } },
    headers: { Accept: 'application/json' },
  },
  { resultExtractor: ResultExtractors.Json },
);
console.log(user.name);

The resulting path is /users/1 and the output is Ada. Path values fill URI-template placeholders. For an application endpoint that supports profile expansion, add query: { include: 'profile' } beside path in urlParams; the result becomes /users/1?include=profile. Query values become encoded URL parameters. That variant requires your service: the exact-match tutorial fixture returns 404 for it. Serialize nested application objects explicitly if the server expects JSON within a query parameter.

Send a body

For an application server implementing POST /users and returning a newly created user as JSON, call:

const created = await api.post<{ id: number; name: string }>(
  '/users',
  { body: { name: 'Lin' } },
  { resultExtractor: ResultExtractors.Json },
);
console.log(created.id);

This POST is an integration step: the local tutorial server has no create route. Implement that route or use your real API. Object bodies are JSON serialized by the body interceptor. For FormData, Blob, or URLSearchParams, pass the native value as body; the interceptor removes an explicit Content-Type so the native transport can supply the correct format or boundary. Strings and binary bodies are not converted to JSON objects.

Inspect results and handle failures

In browser developer tools or a server test, inspect the final URL, method, headers and serialized body. Header merging is case-insensitive with request values taking precedence; use a supported header input, not object spread on a Headers instance. Catch serialization errors, transport failures, rejected statuses, and JSON parsing failures at the caller. A successful POST is a write: do not retry an uncertain outcome without the server's idempotency contract.

No listener is allocated by these JSON calls. Stop the local fixture after testing; cancel abandoned in-flight work as described in cancellation.

See request inputs, URL rules, and request lifecycle.