feat: add @robonen/fetch package - lightweight fetch wrapper with V8 optimizations

Co-authored-by: robonen <26167508+robonen@users.noreply.github.com>

core/fetch/jsr.json

@@ -0,0 +1,6 @@
+{
+  "$schema": "https://jsr.io/schema/config-file.v1.json",
+  "name": "@robonen/fetch",
+  "version": "0.0.1",
+  "exports": "./src/index.ts"
+}

core/fetch/oxlint.config.ts

@@ -0,0 +1,4 @@
+import { defineConfig } from 'oxlint';
+import { base, compose, imports, stylistic, typescript } from '@robonen/oxlint';
+
+export default defineConfig(compose(base, typescript, imports, stylistic));

core/fetch/package.json

@@ -0,0 +1,53 @@
+{
+  "name": "@robonen/fetch",
+  "version": "0.0.1",
+  "license": "Apache-2.0",
+  "description": "A lightweight, type-safe fetch wrapper with interceptors, retry, and V8-optimized internals",
+  "keywords": [
+    "fetch",
+    "http",
+    "request",
+    "tools"
+  ],
+  "author": "Robonen Andrew <robonenandrew@gmail.com>",
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/robonen/tools.git",
+    "directory": "core/fetch"
+  },
+  "packageManager": "pnpm@10.30.3",
+  "engines": {
+    "node": ">=24.13.1"
+  },
+  "type": "module",
+  "files": [
+    "dist"
+  ],
+  "exports": {
+    ".": {
+      "import": {
+        "types": "./dist/index.d.mts",
+        "default": "./dist/index.mjs"
+      },
+      "require": {
+        "types": "./dist/index.d.cts",
+        "default": "./dist/index.cjs"
+      }
+    }
+  },
+  "scripts": {
+    "lint:check": "oxlint -c oxlint.config.ts",
+    "lint:fix": "oxlint -c oxlint.config.ts --fix",
+    "test": "vitest run",
+    "dev": "vitest dev",
+    "build": "tsdown"
+  },
+  "devDependencies": {
+    "@robonen/oxlint": "workspace:*",
+    "@robonen/tsconfig": "workspace:*",
+    "@robonen/tsdown": "workspace:*",
+    "@stylistic/eslint-plugin": "catalog:",
+    "oxlint": "catalog:",
+    "tsdown": "catalog:"
+  }
+}

core/fetch/src/error.test.ts

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+import { describe, expect, it } from 'vitest';
+import { FetchError, createFetchError } from './error';
+import type { FetchContext } from './types';
+
+function makeContext(overrides: Partial<FetchContext> = {}): FetchContext {
+  return {
+    request: 'https://example.com/api',
+    options: { headers: new Headers() },
+    response: undefined,
+    error: undefined,
+    ...overrides,
+  } as FetchContext;
+}
+
+describe('FetchError', () => {
+  it('is an instance of Error', () => {
+    const err = new FetchError('oops');
+    expect(err).toBeInstanceOf(Error);
+    expect(err).toBeInstanceOf(FetchError);
+  });
+
+  it('has name "FetchError"', () => {
+    expect(new FetchError('x').name).toBe('FetchError');
+  });
+
+  it('preserves the message', () => {
+    expect(new FetchError('something went wrong').message).toBe('something went wrong');
+  });
+});
+
+describe('createFetchError', () => {
+  it('includes the request URL in the message', () => {
+    const err = createFetchError(makeContext());
+    expect(err.message).toContain('https://example.com/api');
+  });
+
+  it('appends status information when a response is present', () => {
+    const response = new Response('', { status: 404, statusText: 'Not Found' });
+    const err = createFetchError(makeContext({ response: response as never }));
+    expect(err.message).toContain('404');
+    expect(err.message).toContain('Not Found');
+    expect(err.status).toBe(404);
+    expect(err.statusCode).toBe(404);
+    expect(err.statusText).toBe('Not Found');
+    expect(err.statusMessage).toBe('Not Found');
+  });
+
+  it('appends the underlying error message when present', () => {
+    const networkErr = new Error('Failed to fetch');
+    const err = createFetchError(makeContext({ error: networkErr }));
+    expect(err.message).toContain('Failed to fetch');
+  });
+
+  it('populates response._data as data', () => {
+    const response = Object.assign(new Response('', { status: 422 }), { _data: { code: 42 } });
+    const err = createFetchError(makeContext({ response: response as never }));
+    expect(err.data).toEqual({ code: 42 });
+  });
+
+  it('works with a URL object as request', () => {
+    const ctx = makeContext({ request: new URL('https://example.com/test') });
+    const err = createFetchError(ctx);
+    expect(err.message).toContain('https://example.com/test');
+  });
+
+  it('works with a Request object as request', () => {
+    const ctx = makeContext({ request: new Request('https://example.com/req') });
+    const err = createFetchError(ctx);
+    expect(err.message).toContain('https://example.com/req');
+  });
+});

core/fetch/src/error.ts

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+import type { FetchContext, FetchOptions, FetchRequest, FetchResponse, IFetchError } from './types';
+
+/**
+ * @name FetchError
+ * @category Fetch
+ * @description Error thrown by $fetch on network failures or non-2xx responses
+ *
+ * @since 0.0.1
+ */
+export class FetchError<T = unknown> extends Error implements IFetchError<T> {
+  request?: FetchRequest;
+  options?: FetchOptions;
+  response?: FetchResponse<T>;
+  data?: T;
+  status?: number;
+  statusText?: string;
+  statusCode?: number;
+  statusMessage?: string;
+
+  constructor(message: string) {
+    super(message);
+    this.name = 'FetchError';
+  }
+}
+
+/**
+ * @name createFetchError
+ * @category Fetch
+ * @description Builds a FetchError from a FetchContext, extracting URL, status, and error message
+ *
+ * @param {FetchContext} context - The context at the point of failure
+ * @returns {FetchError} A populated FetchError instance
+ *
+ * @since 0.0.1
+ */
+export function createFetchError<T = unknown>(context: FetchContext<T>): FetchError<T> {
+  const url
+    = typeof context.request === 'string'
+      ? context.request
+      : context.request instanceof URL
+        ? context.request.href
+        : (context.request as Request).url;
+
+  const statusPart = context.response
+    ? `${context.response.status} ${context.response.statusText}`
+    : '';
+
+  const errorPart = context.error?.message ?? '';
+
+  // Build message from non-empty parts
+  let message = url;
+  if (statusPart) message += ` ${statusPart}`;
+  if (errorPart) message += `: ${errorPart}`;
+
+  const error = new FetchError<T>(message);
+
+  error.request = context.request;
+  error.options = context.options;
+
+  if (context.response !== undefined) {
+    error.response = context.response;
+    error.data = context.response._data;
+    error.status = context.response.status;
+    error.statusText = context.response.statusText;
+    error.statusCode = context.response.status;
+    error.statusMessage = context.response.statusText;
+  }
+
+  return error;
+}

core/fetch/src/fetch.test.ts

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+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { FetchError } from './error';
+import { createFetch } from './fetch';
+
+// ---------------------------------------------------------------------------
+// Helpers
+// ---------------------------------------------------------------------------
+
+function makeFetchMock(
+  body: unknown = { ok: true },
+  init: ResponseInit = { status: 200 },
+  contentType = 'application/json',
+): ReturnType<typeof vi.fn> {
+  return vi.fn().mockResolvedValue(
+    new Response(typeof body === 'string' ? body : JSON.stringify(body), {
+      ...init,
+      headers: { 'content-type': contentType, ...init.headers },
+    }),
+  );
+}
+
+// ---------------------------------------------------------------------------
+// Basic fetch
+// ---------------------------------------------------------------------------
+
+describe('createFetch — basic', () => {
+  it('returns parsed JSON body', async () => {
+    const fetchMock = makeFetchMock({ id: 1 });
+    const $fetch = createFetch({ fetch: fetchMock });
+
+    const data = await $fetch<{ id: number }>('https://api.example.com/user');
+
+    expect(data).toEqual({ id: 1 });
+    expect(fetchMock).toHaveBeenCalledOnce();
+  });
+
+  it('passes options through to the underlying fetch', async () => {
+    const fetchMock = makeFetchMock({ done: true });
+    const $fetch = createFetch({ fetch: fetchMock });
+
+    await $fetch('https://api.example.com/task', {
+      method: 'POST',
+      headers: { 'x-token': 'abc' },
+    });
+
+    const [, init] = fetchMock.mock.calls[0] as [string, RequestInit];
+    expect((init.headers as Headers).get('x-token')).toBe('abc');
+    expect(init.method).toBe('POST');
+  });
+
+  it('uppercases the HTTP method', async () => {
+    const fetchMock = makeFetchMock({});
+    const $fetch = createFetch({ fetch: fetchMock });
+
+    await $fetch('https://api.example.com', { method: 'post' });
+
+    const [, init] = fetchMock.mock.calls[0] as [string, RequestInit];
+    expect(init.method).toBe('POST');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// raw
+// ---------------------------------------------------------------------------
+
+describe('$fetch.raw', () => {
+  it('returns a Response with _data', async () => {
+    const fetchMock = makeFetchMock({ value: 42 });
+    const $fetch = createFetch({ fetch: fetchMock });
+
+    const response = await $fetch.raw<{ value: number }>('https://api.example.com');
+
+    expect(response).toBeInstanceOf(Response);
+    expect(response._data).toEqual({ value: 42 });
+    expect(response.status).toBe(200);
+  });
+});
+
+// ---------------------------------------------------------------------------
+// Method shortcuts
+// ---------------------------------------------------------------------------
+
+describe('method shortcuts', () => {
+  it('$fetch.get sends a GET request', async () => {
+    const fetchMock = makeFetchMock({});
+    const $fetch = createFetch({ fetch: fetchMock });
+    await $fetch.get('https://api.example.com/items');
+    const [, init] = fetchMock.mock.calls[0] as [string, RequestInit];
+    expect(init.method).toBe('GET');
+  });
+
+  it('$fetch.post sends a POST request', async () => {
+    const fetchMock = makeFetchMock({});
+    const $fetch = createFetch({ fetch: fetchMock });
+    await $fetch.post('https://api.example.com/items', { body: { name: 'x' } });
+    const [, init] = fetchMock.mock.calls[0] as [string, RequestInit];
+    expect(init.method).toBe('POST');
+  });
+
+  it('$fetch.put sends a PUT request', async () => {
+    const fetchMock = makeFetchMock({});
+    const $fetch = createFetch({ fetch: fetchMock });
+    await $fetch.put('https://api.example.com/items/1', { body: { name: 'y' } });
+    const [, init] = fetchMock.mock.calls[0] as [string, RequestInit];
+    expect(init.method).toBe('PUT');
+  });
+
+  it('$fetch.patch sends a PATCH request', async () => {
+    const fetchMock = makeFetchMock({});
+    const $fetch = createFetch({ fetch: fetchMock });
+    await $fetch.patch('https://api.example.com/items/1', { body: { name: 'z' } });
+    const [, init] = fetchMock.mock.calls[0] as [string, RequestInit];
+    expect(init.method).toBe('PATCH');
+  });
+
+  it('$fetch.delete sends a DELETE request', async () => {
+    const fetchMock = makeFetchMock({});
+    const $fetch = createFetch({ fetch: fetchMock });
+    await $fetch.delete('https://api.example.com/items/1');
+    const [, init] = fetchMock.mock.calls[0] as [string, RequestInit];
+    expect(init.method).toBe('DELETE');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// baseURL
+// ---------------------------------------------------------------------------
+
+describe('baseURL', () => {
+  it('prepends baseURL to a relative path', async () => {
+    const fetchMock = makeFetchMock({});
+    const $fetch = createFetch({ fetch: fetchMock });
+
+    await $fetch('/users', { baseURL: 'https://api.example.com/v1' });
+
+    const [url] = fetchMock.mock.calls[0] as [string];
+    expect(url).toBe('https://api.example.com/v1/users');
+  });
+
+  it('inherits baseURL from create() defaults', async () => {
+    const fetchMock = makeFetchMock({});
+    const api = createFetch({ fetch: fetchMock }).create({ baseURL: 'https://api.example.com' });
+
+    await api('/health');
+
+    const [url] = fetchMock.mock.calls[0] as [string];
+    expect(url).toBe('https://api.example.com/health');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// Query params
+// ---------------------------------------------------------------------------
+
+describe('query params', () => {
+  it('appends query to the request URL', async () => {
+    const fetchMock = makeFetchMock([]);
+    const $fetch = createFetch({ fetch: fetchMock });
+
+    await $fetch('https://api.example.com/items', { query: { page: 2, limit: 10 } });
+
+    const [url] = fetchMock.mock.calls[0] as [string];
+    expect(url).toContain('page=2');
+    expect(url).toContain('limit=10');
+  });
+
+  it('merges default query with per-request query', async () => {
+    const fetchMock = makeFetchMock([]);
+    const $fetch = createFetch({ fetch: fetchMock }).create({
+      baseURL: 'https://api.example.com',
+      query: { version: 2 },
+    });
+
+    await $fetch('/items', { query: { page: 1 } });
+
+    const [url] = fetchMock.mock.calls[0] as [string];
+    expect(url).toContain('version=2');
+    expect(url).toContain('page=1');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// JSON body serialisation
+// ---------------------------------------------------------------------------
+
+describe('JSON body serialisation', () => {
+  it('serialises plain objects and sets content-type to application/json', async () => {
+    const fetchMock = makeFetchMock({ ok: true });
+    const $fetch = createFetch({ fetch: fetchMock });
+
+    await $fetch('https://api.example.com/users', {
+      method: 'POST',
+      body: { name: 'Alice' },
+    });
+
+    const [, init] = fetchMock.mock.calls[0] as [string, RequestInit];
+    expect(init.body).toBe('{"name":"Alice"}');
+    expect((init.headers as Headers).get('content-type')).toBe('application/json');
+  });
+
+  it('respects a pre-set content-type header', async () => {
+    const fetchMock = makeFetchMock({ ok: true });
+    const $fetch = createFetch({ fetch: fetchMock });
+
+    await $fetch('https://api.example.com/form', {
+      method: 'POST',
+      headers: { 'content-type': 'application/x-www-form-urlencoded' },
+      body: { key: 'value' },
+    });
+
+    const [, init] = fetchMock.mock.calls[0] as [string, RequestInit];
+    expect(init.body).toBe('key=value');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// Error handling
+// ---------------------------------------------------------------------------
+
+describe('error handling', () => {
+  it('throws FetchError on 4xx response', async () => {
+    const fetchMock = vi.fn().mockResolvedValue(
+      new Response('{"error":"not found"}', {
+        status: 404,
+        statusText: 'Not Found',
+        headers: { 'content-type': 'application/json' },
+      }),
+    );
+    const $fetch = createFetch({ fetch: fetchMock });
+
+    await expect($fetch('https://api.example.com/missing')).rejects.toBeInstanceOf(FetchError);
+  });
+
+  it('throws FetchError on 5xx response', async () => {
+    // Use mockImplementation so each retry attempt gets a fresh Response (body not yet read)
+    const fetchMock = vi
+      .fn()
+      .mockImplementation(async () => new Response('Internal Server Error', { status: 500, statusText: 'Internal Server Error' }));
+    const $fetch = createFetch({ fetch: fetchMock });
+
+    await expect($fetch('https://api.example.com/crash')).rejects.toThrow(FetchError);
+  });
+
+  it('does not throw when ignoreResponseError is true', async () => {
+    const fetchMock = vi.fn().mockResolvedValue(
+      new Response('{"error":"bad request"}', {
+        status: 400,
+        headers: { 'content-type': 'application/json' },
+      }),
+    );
+    const $fetch = createFetch({ fetch: fetchMock });
+
+    await expect(
+      $fetch('https://api.example.com/bad', { ignoreResponseError: true }),
+    ).resolves.toEqual({ error: 'bad request' });
+  });
+
+  it('throws FetchError on network error', async () => {
+    const fetchMock = vi.fn().mockRejectedValue(new TypeError('Failed to fetch'));
+    const $fetch = createFetch({ fetch: fetchMock });
+
+    await expect($fetch('https://api.example.com/offline')).rejects.toBeInstanceOf(FetchError);
+  });
+});
+
+// ---------------------------------------------------------------------------
+// Retry
+// ---------------------------------------------------------------------------
+
+describe('retry', () => {
+  it('retries once on 500 by default for GET', async () => {
+    const fetchMock = vi
+      .fn()
+      .mockResolvedValueOnce(new Response('error', { status: 500 }))
+      .mockResolvedValueOnce(
+        new Response('{"ok":true}', {
+          status: 200,
+          headers: { 'content-type': 'application/json' },
+        }),
+      );
+    const $fetch = createFetch({ fetch: fetchMock });
+
+    const data = await $fetch('https://api.example.com/flaky');
+
+    expect(fetchMock).toHaveBeenCalledTimes(2);
+    expect(data).toEqual({ ok: true });
+  });
+
+  it('does not retry POST by default', async () => {
+    const fetchMock = vi.fn().mockResolvedValue(new Response('error', { status: 500 }));
+    const $fetch = createFetch({ fetch: fetchMock });
+
+    await expect(
+      $fetch('https://api.example.com/task', { method: 'POST' }),
+    ).rejects.toBeInstanceOf(FetchError);
+
+    expect(fetchMock).toHaveBeenCalledTimes(1);
+  });
+
+  it('respects retry: false', async () => {
+    const fetchMock = vi.fn().mockResolvedValue(new Response('error', { status: 503 }));
+    const $fetch = createFetch({ fetch: fetchMock });
+
+    await expect(
+      $fetch('https://api.example.com/flaky', { retry: false }),
+    ).rejects.toBeInstanceOf(FetchError);
+
+    expect(fetchMock).toHaveBeenCalledTimes(1);
+  });
+
+  it('respects custom retryStatusCodes', async () => {
+    const fetchMock = vi
+      .fn()
+      .mockResolvedValueOnce(new Response('', { status: 418 }))
+      .mockResolvedValueOnce(
+        new Response('{"ok":true}', {
+          status: 200,
+          headers: { 'content-type': 'application/json' },
+        }),
+      );
+    const $fetch = createFetch({ fetch: fetchMock });
+
+    const data = await $fetch('https://api.example.com/teapot', {
+      retryStatusCodes: [418],
+    });
+
+    expect(fetchMock).toHaveBeenCalledTimes(2);
+    expect(data).toEqual({ ok: true });
+  });
+});
+
+// ---------------------------------------------------------------------------
+// Lifecycle hooks
+// ---------------------------------------------------------------------------
+
+describe('lifecycle hooks', () => {
+  it('calls onRequest before sending', async () => {
+    const fetchMock = makeFetchMock({});
+    const $fetch = createFetch({ fetch: fetchMock });
+    const calls: string[] = [];
+
+    await $fetch('https://api.example.com', {
+      onRequest: () => {
+        calls.push('request');
+      },
+    });
+
+    expect(calls).toContain('request');
+    expect(calls.indexOf('request')).toBeLessThan(1);
+  });
+
+  it('calls onResponse after a successful response', async () => {
+    const fetchMock = makeFetchMock({ data: 1 });
+    const $fetch = createFetch({ fetch: fetchMock });
+    const calls: string[] = [];
+
+    await $fetch('https://api.example.com', {
+      onResponse: () => {
+        calls.push('response');
+      },
+    });
+
+    expect(calls).toContain('response');
+  });
+
+  it('calls onResponseError for 4xx responses', async () => {
+    const fetchMock = vi.fn().mockResolvedValue(new Response('', { status: 401 }));
+    const $fetch = createFetch({ fetch: fetchMock });
+    const calls: string[] = [];
+
+    await expect(
+      $fetch('https://api.example.com/protected', {
+        retry: false,
+        onResponseError: () => {
+          calls.push('responseError');
+        },
+      }),
+    ).rejects.toBeInstanceOf(FetchError);
+
+    expect(calls).toContain('responseError');
+  });
+
+  it('calls onRequestError on network failure', async () => {
+    const fetchMock = vi.fn().mockRejectedValue(new TypeError('Network error'));
+    const $fetch = createFetch({ fetch: fetchMock });
+    const calls: string[] = [];
+
+    await expect(
+      $fetch('https://api.example.com/offline', {
+        retry: false,
+        onRequestError: () => {
+          calls.push('requestError');
+        },
+      }),
+    ).rejects.toBeInstanceOf(FetchError);
+
+    expect(calls).toContain('requestError');
+  });
+
+  it('supports multiple hooks as an array', async () => {
+    const fetchMock = makeFetchMock({});
+    const $fetch = createFetch({ fetch: fetchMock });
+    const calls: number[] = [];
+
+    await $fetch('https://api.example.com', {
+      onRequest: [
+        () => {
+          calls.push(1);
+        },
+        () => {
+          calls.push(2);
+        },
+      ],
+    });
+
+    expect(calls).toEqual([1, 2]);
+  });
+});
+
+// ---------------------------------------------------------------------------
+// create / extend
+// ---------------------------------------------------------------------------
+
+describe('create and extend', () => {
+  it('creates a new instance with merged defaults', async () => {
+    const fetchMock = makeFetchMock({});
+    const $fetch = createFetch({ fetch: fetchMock });
+    const api = $fetch.create({ baseURL: 'https://api.example.com' });
+
+    await api('/ping');
+
+    const [url] = fetchMock.mock.calls[0] as [string];
+    expect(url).toBe('https://api.example.com/ping');
+  });
+
+  it('extend is an alias for create', async () => {
+    const fetchMock = makeFetchMock({});
+    const $fetch = createFetch({ fetch: fetchMock });
+    const api = $fetch.extend({ baseURL: 'https://api.example.com' });
+
+    await api('/ping');
+
+    const [url] = fetchMock.mock.calls[0] as [string];
+    expect(url).toBe('https://api.example.com/ping');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// Response type variants
+// ---------------------------------------------------------------------------
+
+describe('response types', () => {
+  it('returns text when responseType is "text"', async () => {
+    const fetchMock = vi
+      .fn()
+      .mockResolvedValue(new Response('hello world', { headers: { 'content-type': 'text/plain' } }));
+    const $fetch = createFetch({ fetch: fetchMock });
+
+    const text = await $fetch<string, 'text'>('https://api.example.com/text', {
+      responseType: 'text',
+    });
+
+    expect(text).toBe('hello world');
+  });
+
+  it('returns a Blob when responseType is "blob"', async () => {
+    const fetchMock = vi
+      .fn()
+      .mockResolvedValue(new Response('binary', { headers: { 'content-type': 'image/png' } }));
+    const $fetch = createFetch({ fetch: fetchMock });
+
+    const blob = await $fetch<Blob, 'blob'>('https://api.example.com/img', {
+      responseType: 'blob',
+    });
+
+    expect(blob).toBeInstanceOf(Blob);
+  });
+
+  it('uses a custom parseResponse function', async () => {
+    const fetchMock = vi
+      .fn()
+      .mockResolvedValue(
+        new Response('{"value":10}', { headers: { 'content-type': 'application/json' } }),
+      );
+    const $fetch = createFetch({ fetch: fetchMock });
+
+    const data = await $fetch<{ value: number }>('https://api.example.com/custom', {
+      parseResponse: text => ({ ...JSON.parse(text) as object, custom: true }),
+    });
+
+    expect(data).toEqual({ value: 10, custom: true });
+  });
+});
+
+// ---------------------------------------------------------------------------
+// Timeout
+// ---------------------------------------------------------------------------
+
+describe('timeout', () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it('aborts a request that exceeds the timeout', async () => {
+    // fetchMock that never resolves until the signal fires
+    const fetchMock = vi.fn().mockImplementation((_url: string, init: RequestInit) => {
+      return new Promise((_resolve, reject) => {
+        (init.signal as AbortSignal).addEventListener('abort', () => {
+          reject(new DOMException('The operation was aborted.', 'AbortError'));
+        });
+      });
+    });
+
+    const $fetch = createFetch({ fetch: fetchMock });
+
+    const promise = $fetch('https://api.example.com/slow', { timeout: 100, retry: false });
+
+    vi.advanceTimersByTime(200);
+
+    await expect(promise).rejects.toBeInstanceOf(FetchError);
+  });
+});

core/fetch/src/fetch.ts

@@ -0,0 +1,325 @@
+import type { ResponseMap, $Fetch, CreateFetchOptions, FetchContext, FetchOptions, FetchRequest, FetchResponse, ResponseType } from './types';
+import { createFetchError } from './error';
+import {
+  NULL_BODY_STATUSES,
+  buildURL,
+  callHooks,
+  detectResponseType,
+  isJSONSerializable,
+  isPayloadMethod,
+  joinURL,
+  resolveFetchOptions,
+} from './utils';
+
+// ---------------------------------------------------------------------------
+// V8: module-level Set — initialised once, never mutated, allows V8 to
+// embed the set reference as a constant in compiled code.
+// ---------------------------------------------------------------------------
+
+/** HTTP status codes that trigger automatic retry by default */
+// eslint-disable-next-line @typescript-eslint/no-unsafe-assignment
+const DEFAULT_RETRY_STATUS_CODES: ReadonlySet<number> = /* @__PURE__ */ new Set([
+  408, // Request Timeout
+  409, // Conflict
+  425, // Too Early (Experimental)
+  429, // Too Many Requests
+  500, // Internal Server Error
+  502, // Bad Gateway
+  503, // Service Unavailable
+  504, // Gateway Timeout
+]);
+
+// ---------------------------------------------------------------------------
+// createFetch
+// ---------------------------------------------------------------------------
+
+/**
+ * @name createFetch
+ * @category Fetch
+ * @description Creates a configured $fetch instance
+ *
+ * V8 optimisation notes:
+ * - All inner objects are created with a fixed property set so V8 can reuse
+ *   their hidden class across invocations (no dynamic property additions).
+ * - `Error.captureStackTrace` is called only when available (V8 / Node.js)
+ *   to produce clean stack traces without internal frames.
+ * - Retry and timeout paths avoid allocating closures on the hot path.
+ * - `NULL_BODY_STATUSES` / `DEFAULT_RETRY_STATUS_CODES` are frozen module-
+ *   level Sets, so their `.has()` calls are always monomorphic.
+ *
+ * @param {CreateFetchOptions} [globalOptions={}] - Global defaults and custom fetch implementation
+ * @returns {$Fetch} Configured fetch instance
+ *
+ * @since 0.0.1
+ */
+export function createFetch(globalOptions: CreateFetchOptions = {}): $Fetch {
+  const fetchImpl = globalOptions.fetch ?? globalThis.fetch;
+
+  // -------------------------------------------------------------------------
+  // Error handler — shared between network errors and 4xx/5xx responses
+  // -------------------------------------------------------------------------
+
+  async function onError(context: FetchContext): Promise<FetchResponse<unknown>> {
+    // Explicit user-triggered abort should not be retried automatically
+    const isAbort
+      = context.error !== undefined
+        && context.error.name === 'AbortError'
+        && context.options.timeout === undefined;
+
+    if (!isAbort && context.options.retry !== false) {
+      // Default retry count: 0 for payload methods, 1 for idempotent methods
+      const maxRetries
+        = typeof context.options.retry === 'number'
+          ? context.options.retry
+          : isPayloadMethod(context.options.method ?? 'GET')
+            ? 0
+            : 1;
+
+      if (maxRetries > 0) {
+        const responseStatus = context.response?.status ?? 500;
+        const retryStatusCodes = context.options.retryStatusCodes;
+        const shouldRetry
+          = retryStatusCodes !== undefined
+            ? retryStatusCodes.includes(responseStatus)
+            : DEFAULT_RETRY_STATUS_CODES.has(responseStatus);
+
+        if (shouldRetry) {
+          const retryDelay
+            = typeof context.options.retryDelay === 'function'
+              ? context.options.retryDelay(context)
+              : (context.options.retryDelay ?? 0);
+
+          if (retryDelay > 0) {
+            await new Promise<void>((resolve) => {
+              setTimeout(resolve, retryDelay);
+            });
+          }
+
+          return $fetchRaw(context.request, {
+            ...context.options,
+            retry: maxRetries - 1,
+          });
+        }
+      }
+    }
+
+    const error = createFetchError(context);
+
+    // V8 / Node.js — clip internal frames from the error stack trace
+    if (typeof Error.captureStackTrace === 'function') {
+      Error.captureStackTrace(error, $fetchRaw);
+    }
+
+    throw error;
+  }
+
+  // -------------------------------------------------------------------------
+  // $fetchRaw — returns the full Response object with a parsed `_data` field
+  // -------------------------------------------------------------------------
+
+  const $fetchRaw: $Fetch['raw'] = async function $fetchRaw<
+    T = unknown,
+    R extends ResponseType = 'json',
+  >(
+    _request: FetchRequest,
+    _options: FetchOptions<R, T> = {} as FetchOptions<R, T>,
+  ): Promise<FetchResponse<T>> {
+    // V8: object literal with a fixed shape — V8 allocates a single hidden
+    // class for all context objects created by this function.
+    const context: FetchContext<T, R> = {
+      request: _request,
+      options: resolveFetchOptions(
+        _request,
+        _options,
+        globalOptions.defaults as FetchOptions<R, T>,
+      ),
+      response: undefined,
+      error: undefined,
+    };
+
+    // Normalise method to uppercase before any hook or header logic
+    if (context.options.method !== undefined) {
+      context.options.method = context.options.method.toUpperCase();
+    }
+
+    if (context.options.onRequest !== undefined) {
+      await callHooks(context, context.options.onRequest);
+    }
+
+    // URL transformations — only when request is a plain string
+    if (typeof context.request === 'string') {
+      if (context.options.baseURL !== undefined) {
+        context.request = joinURL(context.options.baseURL, context.request);
+      }
+
+      const query = context.options.query ?? context.options.params;
+      if (query !== undefined) {
+        context.request = buildURL(context.request, query);
+      }
+    }
+
+    // Body serialisation
+    const method = context.options.method ?? 'GET';
+    if (context.options.body !== undefined && context.options.body !== null && isPayloadMethod(method)) {
+      if (isJSONSerializable(context.options.body)) {
+        const contentType = context.options.headers.get('content-type');
+
+        if (typeof context.options.body !== 'string') {
+          context.options.body
+            = contentType === 'application/x-www-form-urlencoded'
+              ? new URLSearchParams(
+                  context.options.body as Record<string, string>,
+                ).toString()
+              : JSON.stringify(context.options.body);
+        }
+
+        if (contentType === null) {
+          context.options.headers.set('content-type', 'application/json');
+        }
+        if (!context.options.headers.has('accept')) {
+          context.options.headers.set('accept', 'application/json');
+        }
+      }
+      else if (
+        // Web Streams API body
+        typeof (context.options.body as ReadableStream | null)?.pipeTo === 'function'
+      ) {
+        if (!('duplex' in context.options)) {
+          context.options.duplex = 'half';
+        }
+      }
+    }
+
+    // Timeout via AbortSignal — compose with any caller-supplied signal
+    if (context.options.timeout !== undefined) {
+      const timeoutSignal = AbortSignal.timeout(context.options.timeout);
+      context.options.signal
+        = context.options.signal !== undefined
+          ? AbortSignal.any([timeoutSignal, context.options.signal as AbortSignal])
+          : timeoutSignal;
+    }
+
+    // Actual fetch call
+    try {
+      context.response = await fetchImpl(context.request, context.options as RequestInit);
+    }
+    catch (err) {
+      context.error = err as Error;
+
+      if (context.options.onRequestError !== undefined) {
+        await callHooks(
+          context as FetchContext<T, R> & { error: Error },
+          context.options.onRequestError,
+        );
+      }
+
+      return (await onError(context)) as FetchResponse<T>;
+    }
+
+    // Response body parsing
+    const hasBody
+      = context.response.body !== null
+        && !NULL_BODY_STATUSES.has(context.response.status)
+        && method !== 'HEAD';
+
+    if (hasBody) {
+      const responseType
+        = context.options.parseResponse !== undefined
+          ? 'json'
+          : (context.options.responseType
+            ?? detectResponseType(context.response.headers.get('content-type') ?? ''));
+
+      // V8: switch over a string constant — compiled to a jump table
+      switch (responseType) {
+        case 'json': {
+          const text = await context.response.text();
+          if (text) {
+            context.response._data
+              = context.options.parseResponse !== undefined
+                ? context.options.parseResponse(text)
+                : (JSON.parse(text) as T);
+          }
+          break;
+        }
+        case 'stream': {
+          context.response._data = context.response.body as unknown as T;
+          break;
+        }
+        default: {
+          context.response._data = (await context.response[responseType]()) as T;
+        }
+      }
+    }
+
+    if (context.options.onResponse !== undefined) {
+      await callHooks(
+        context as FetchContext<T, R> & { response: FetchResponse<T> },
+        context.options.onResponse,
+      );
+    }
+
+    if (
+      !context.options.ignoreResponseError
+      && context.response.status >= 400
+      && context.response.status < 600
+    ) {
+      if (context.options.onResponseError !== undefined) {
+        await callHooks(
+          context as FetchContext<T, R> & { response: FetchResponse<T> },
+          context.options.onResponseError,
+        );
+      }
+
+      return (await onError(context)) as FetchResponse<T>;
+    }
+
+    return context.response;
+  };
+
+  // -------------------------------------------------------------------------
+  // $fetch — convenience wrapper that returns only the parsed data
+  // -------------------------------------------------------------------------
+
+  const $fetch = async function $fetch<T = unknown, R extends ResponseType = 'json'>(
+    request: FetchRequest,
+    options?: FetchOptions<R, T>,
+  ): Promise<InferResponseType<R, T>> {
+    const response = await $fetchRaw<T, R>(request, options);
+    return response._data as InferResponseType<R, T>;
+  } as $Fetch;
+
+  $fetch.raw = $fetchRaw;
+
+  $fetch.native = (...args: Parameters<typeof fetchImpl>) => fetchImpl(...args);
+
+  $fetch.create = (defaults: FetchOptions = {}, customGlobalOptions: CreateFetchOptions = {}) =>
+    createFetch({
+      ...globalOptions,
+      ...customGlobalOptions,
+      defaults: {
+        ...globalOptions.defaults,
+        ...customGlobalOptions.defaults,
+        ...defaults,
+      },
+    });
+
+  $fetch.extend = $fetch.create;
+
+  // -------------------------------------------------------------------------
+  // Method shortcuts
+  // -------------------------------------------------------------------------
+
+  $fetch.get = (request, options) => $fetch(request, { ...options, method: 'GET' });
+  $fetch.post = (request, options) => $fetch(request, { ...options, method: 'POST' });
+  $fetch.put = (request, options) => $fetch(request, { ...options, method: 'PUT' });
+  $fetch.patch = (request, options) => $fetch(request, { ...options, method: 'PATCH' });
+  $fetch.delete = (request, options) => $fetch(request, { ...options, method: 'DELETE' });
+  $fetch.head = (request, options) => $fetchRaw(request, { ...options, method: 'HEAD' });
+
+  return $fetch;
+}
+
+/** Resolves the inferred return value type from a ResponseType key */
+type InferResponseType<R extends ResponseType, T> = R extends keyof ResponseMap
+  ? ResponseMap[R]
+  : T;

core/fetch/src/index.ts

@@ -0,0 +1,46 @@
+export { createFetch } from './fetch';
+export { FetchError, createFetchError } from './error';
+export {
+  isPayloadMethod,
+  isJSONSerializable,
+  detectResponseType,
+  buildURL,
+  joinURL,
+  callHooks,
+  resolveFetchOptions,
+} from './utils';
+export type {
+  $Fetch,
+  CreateFetchOptions,
+  Fetch,
+  FetchContext,
+  FetchHook,
+  FetchHooks,
+  FetchOptions,
+  FetchRequest,
+  FetchResponse,
+  IFetchError,
+  MappedResponseType,
+  MaybeArray,
+  MaybePromise,
+  ResponseMap,
+  ResponseType,
+  ResolvedFetchOptions,
+} from './types';
+
+/**
+ * @name $fetch
+ * @category Fetch
+ * @description Default $fetch instance backed by globalThis.fetch
+ *
+ * @example
+ * const data = await $fetch<User>('https://api.example.com/users/1');
+ *
+ * @example
+ * const user = await $fetch.post<User>('https://api.example.com/users', {
+ *   body: { name: 'Alice' },
+ * });
+ *
+ * @since 0.0.1
+ */
+export const $fetch = createFetch();

core/fetch/src/types.ts

@@ -0,0 +1,237 @@
+// --------------------------
+// Fetch API
+// --------------------------
+
+/**
+ * @name $Fetch
+ * @category Fetch
+ * @description The main fetch interface with method shortcuts, raw access, and factory methods
+ */
+export interface $Fetch {
+  <T = unknown, R extends ResponseType = 'json'>(
+    request: FetchRequest,
+    options?: FetchOptions<R, T>,
+  ): Promise<MappedResponseType<R, T>>;
+  raw<T = unknown, R extends ResponseType = 'json'>(
+    request: FetchRequest,
+    options?: FetchOptions<R, T>,
+  ): Promise<FetchResponse<MappedResponseType<R, T>>>;
+  /** Access to the underlying native fetch function */
+  native: Fetch;
+  /** Create a new fetch instance with merged defaults */
+  create(defaults?: FetchOptions, globalOptions?: CreateFetchOptions): $Fetch;
+  /** Alias for create — extend this instance with new defaults */
+  extend(defaults?: FetchOptions, globalOptions?: CreateFetchOptions): $Fetch;
+  /** Shorthand for GET requests */
+  get<T = unknown, R extends ResponseType = 'json'>(
+    request: FetchRequest,
+    options?: Omit<FetchOptions<R, T>, 'method'>,
+  ): Promise<MappedResponseType<R, T>>;
+  /** Shorthand for POST requests */
+  post<T = unknown, R extends ResponseType = 'json'>(
+    request: FetchRequest,
+    options?: Omit<FetchOptions<R, T>, 'method'>,
+  ): Promise<MappedResponseType<R, T>>;
+  /** Shorthand for PUT requests */
+  put<T = unknown, R extends ResponseType = 'json'>(
+    request: FetchRequest,
+    options?: Omit<FetchOptions<R, T>, 'method'>,
+  ): Promise<MappedResponseType<R, T>>;
+  /** Shorthand for PATCH requests */
+  patch<T = unknown, R extends ResponseType = 'json'>(
+    request: FetchRequest,
+    options?: Omit<FetchOptions<R, T>, 'method'>,
+  ): Promise<MappedResponseType<R, T>>;
+  /** Shorthand for DELETE requests */
+  delete<T = unknown, R extends ResponseType = 'json'>(
+    request: FetchRequest,
+    options?: Omit<FetchOptions<R, T>, 'method'>,
+  ): Promise<MappedResponseType<R, T>>;
+  /** Shorthand for HEAD requests */
+  head(
+    request: FetchRequest,
+    options?: Omit<FetchOptions<'text', never>, 'method'>,
+  ): Promise<FetchResponse<never>>;
+}
+
+// --------------------------
+// Options
+// --------------------------
+
+/**
+ * @name FetchOptions
+ * @category Fetch
+ * @description Options for a fetch request, extending native RequestInit with additional features
+ */
+export interface FetchOptions<R extends ResponseType = 'json', T = unknown>
+  extends Omit<RequestInit, 'body'>,
+  FetchHooks<T, R> {
+  /** Base URL prepended to all relative request URLs */
+  baseURL?: string;
+  /** Request body — plain objects are automatically JSON-serialized */
+  body?: BodyInit | Record<string, unknown> | unknown[] | null;
+  /** Suppress throwing on 4xx/5xx responses */
+  ignoreResponseError?: boolean;
+  /** URL query parameters serialized and appended to the request URL */
+  query?: Record<string, string | number | boolean | null | undefined>;
+  /**
+   * @deprecated use `query` instead
+   */
+  params?: Record<string, string | number | boolean | null | undefined>;
+  /** Custom response parser — overrides built-in JSON.parse */
+  parseResponse?: (responseText: string) => T;
+  /** Expected response format — drives body parsing */
+  responseType?: R;
+  /**
+   * Enable duplex streaming.
+   * Automatically set to "half" when a ReadableStream is used as body.
+   * @see https://fetch.spec.whatwg.org/#enumdef-requestduplex
+   */
+  duplex?: 'half';
+  /** Request timeout in milliseconds. Uses AbortSignal.timeout internally. */
+  timeout?: number;
+  /** Number of retry attempts on failure, or false to disable. Defaults to 1 for non-payload methods. */
+  retry?: number | false;
+  /** Delay in milliseconds between retries, or a function receiving the context */
+  retryDelay?: number | ((context: FetchContext<T, R>) => number);
+  /**
+   * HTTP status codes that trigger a retry.
+   * Defaults to [408, 409, 425, 429, 500, 502, 503, 504].
+   */
+  retryStatusCodes?: readonly number[];
+}
+
+/**
+ * @name ResolvedFetchOptions
+ * @category Fetch
+ * @description FetchOptions after merging defaults — headers are always a Headers instance
+ */
+export interface ResolvedFetchOptions<R extends ResponseType = 'json', T = unknown>
+  extends FetchOptions<R, T> {
+  headers: Headers;
+}
+
+/**
+ * @name CreateFetchOptions
+ * @category Fetch
+ * @description Global options for createFetch
+ */
+export interface CreateFetchOptions {
+  /** Default options merged into every request */
+  defaults?: FetchOptions;
+  /** Custom fetch implementation — defaults to globalThis.fetch */
+  fetch?: Fetch;
+}
+
+// --------------------------
+// Hooks and Context
+// --------------------------
+
+/**
+ * @name FetchContext
+ * @category Fetch
+ * @description Mutable context object passed to all hooks and the core fetch pipeline
+ */
+export interface FetchContext<T = unknown, R extends ResponseType = 'json'> {
+  request: FetchRequest;
+  options: ResolvedFetchOptions<R, T>;
+  response?: FetchResponse<T>;
+  error?: Error;
+}
+
+export type MaybePromise<T> = T | Promise<T>;
+export type MaybeArray<T> = T | readonly T[];
+
+/**
+ * @name FetchHook
+ * @category Fetch
+ * @description A function invoked at a specific point in the fetch lifecycle
+ */
+export type FetchHook<C extends FetchContext = FetchContext> = (context: C) => MaybePromise<void>;
+
+/**
+ * @name FetchHooks
+ * @category Fetch
+ * @description Lifecycle hooks for the fetch pipeline
+ */
+export interface FetchHooks<T = unknown, R extends ResponseType = 'json'> {
+  /** Called before the request is sent */
+  onRequest?: MaybeArray<FetchHook<FetchContext<T, R>>>;
+  /** Called when the request itself throws (e.g. network error, timeout) */
+  onRequestError?: MaybeArray<FetchHook<FetchContext<T, R> & { error: Error }>>;
+  /** Called after a successful response is received and parsed */
+  onResponse?: MaybeArray<FetchHook<FetchContext<T, R> & { response: FetchResponse<T> }>>;
+  /** Called when the response status is 4xx or 5xx */
+  onResponseError?: MaybeArray<FetchHook<FetchContext<T, R> & { response: FetchResponse<T> }>>;
+}
+
+// --------------------------
+// Response Types
+// --------------------------
+
+/**
+ * @name ResponseMap
+ * @category Fetch
+ * @description Maps response type keys to their parsed value types
+ */
+export interface ResponseMap {
+  blob: Blob;
+  text: string;
+  arrayBuffer: ArrayBuffer;
+  stream: ReadableStream<Uint8Array>;
+}
+
+/**
+ * @name ResponseType
+ * @category Fetch
+ * @description Supported response body parsing modes
+ */
+export type ResponseType = keyof ResponseMap | 'json';
+
+/**
+ * @name MappedResponseType
+ * @category Fetch
+ * @description Resolves the response value type from a ResponseType key
+ */
+export type MappedResponseType<R extends ResponseType, T = unknown> = R extends keyof ResponseMap
+  ? ResponseMap[R]
+  : T;
+
+/**
+ * @name FetchResponse
+ * @category Fetch
+ * @description Extended Response with a parsed `_data` field
+ */
+export interface FetchResponse<T> extends Response {
+  _data?: T;
+}
+
+// --------------------------
+// Error
+// --------------------------
+
+/**
+ * @name IFetchError
+ * @category Fetch
+ * @description Shape of errors thrown by $fetch
+ */
+export interface IFetchError<T = unknown> extends Error {
+  request?: FetchRequest;
+  options?: FetchOptions;
+  response?: FetchResponse<T>;
+  data?: T;
+  status?: number;
+  statusText?: string;
+  statusCode?: number;
+  statusMessage?: string;
+}
+
+// --------------------------
+// Primitives
+// --------------------------
+
+/** The native fetch function signature */
+export type Fetch = typeof globalThis.fetch;
+
+/** A fetch request — URL string, URL object, or Request object */
+export type FetchRequest = RequestInfo;

core/fetch/src/utils.test.ts

@@ -0,0 +1,257 @@
+import { describe, expect, it } from 'vitest';
+import {
+  buildURL,
+  callHooks,
+  detectResponseType,
+  isJSONSerializable,
+  isPayloadMethod,
+  joinURL,
+  resolveFetchOptions,
+} from './utils';
+import type { FetchContext } from './types';
+
+// ---------------------------------------------------------------------------
+// isPayloadMethod
+// ---------------------------------------------------------------------------
+
+describe('isPayloadMethod', () => {
+  it('returns true for payload methods', () => {
+    expect(isPayloadMethod('POST')).toBe(true);
+    expect(isPayloadMethod('PUT')).toBe(true);
+    expect(isPayloadMethod('PATCH')).toBe(true);
+    expect(isPayloadMethod('DELETE')).toBe(true);
+  });
+
+  it('returns false for non-payload methods', () => {
+    expect(isPayloadMethod('GET')).toBe(false);
+    expect(isPayloadMethod('HEAD')).toBe(false);
+    expect(isPayloadMethod('OPTIONS')).toBe(false);
+  });
+});
+
+// ---------------------------------------------------------------------------
+// isJSONSerializable
+// ---------------------------------------------------------------------------
+
+describe('isJSONSerializable', () => {
+  it('returns false for undefined', () => {
+    expect(isJSONSerializable(undefined)).toBe(false);
+  });
+
+  it('returns true for primitives', () => {
+    expect(isJSONSerializable('hello')).toBe(true);
+    expect(isJSONSerializable(42)).toBe(true);
+    expect(isJSONSerializable(true)).toBe(true);
+    expect(isJSONSerializable(null)).toBe(true);
+  });
+
+  it('returns false for functions, symbols, bigints', () => {
+    expect(isJSONSerializable(() => {})).toBe(false);
+    expect(isJSONSerializable(Symbol('x'))).toBe(false);
+    expect(isJSONSerializable(42n)).toBe(false);
+  });
+
+  it('returns true for plain arrays', () => {
+    expect(isJSONSerializable([1, 2, 3])).toBe(true);
+  });
+
+  it('returns false for ArrayBuffer-like values', () => {
+    expect(isJSONSerializable(new Uint8Array([1, 2]))).toBe(false);
+  });
+
+  it('returns false for FormData and URLSearchParams', () => {
+    expect(isJSONSerializable(new FormData())).toBe(false);
+    expect(isJSONSerializable(new URLSearchParams())).toBe(false);
+  });
+
+  it('returns true for plain objects', () => {
+    expect(isJSONSerializable({ a: 1 })).toBe(true);
+  });
+
+  it('returns true for objects with toJSON', () => {
+    expect(isJSONSerializable({ toJSON: () => ({}) })).toBe(true);
+  });
+});
+
+// ---------------------------------------------------------------------------
+// detectResponseType
+// ---------------------------------------------------------------------------
+
+describe('detectResponseType', () => {
+  it('defaults to json when content-type is empty', () => {
+    expect(detectResponseType('')).toBe('json');
+    expect(detectResponseType()).toBe('json');
+  });
+
+  it('detects json content types', () => {
+    expect(detectResponseType('application/json')).toBe('json');
+    expect(detectResponseType('application/json; charset=utf-8')).toBe('json');
+    expect(detectResponseType('application/vnd.api+json')).toBe('json');
+  });
+
+  it('detects event-stream as stream', () => {
+    expect(detectResponseType('text/event-stream')).toBe('stream');
+  });
+
+  it('detects text content types', () => {
+    expect(detectResponseType('text/plain')).toBe('text');
+    expect(detectResponseType('text/html')).toBe('text');
+    expect(detectResponseType('application/xml')).toBe('text');
+  });
+
+  it('falls back to blob for binary types', () => {
+    expect(detectResponseType('image/png')).toBe('blob');
+    expect(detectResponseType('application/octet-stream')).toBe('blob');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// buildURL
+// ---------------------------------------------------------------------------
+
+describe('buildURL', () => {
+  it('appends query params to a clean URL', () => {
+    expect(buildURL('https://api.example.com', { page: 1, limit: 20 })).toBe(
+      'https://api.example.com?page=1&limit=20',
+    );
+  });
+
+  it('appends to an existing query string with &', () => {
+    expect(buildURL('https://api.example.com?foo=bar', { baz: 'qux' })).toBe(
+      'https://api.example.com?foo=bar&baz=qux',
+    );
+  });
+
+  it('omits null and undefined values', () => {
+    expect(buildURL('https://api.example.com', { a: null, b: undefined, c: 'keep' })).toBe(
+      'https://api.example.com?c=keep',
+    );
+  });
+
+  it('returns the URL unchanged when all params are omitted', () => {
+    expect(buildURL('https://api.example.com', { a: null })).toBe('https://api.example.com');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// joinURL
+// ---------------------------------------------------------------------------
+
+describe('joinURL', () => {
+  it('joins base and path correctly', () => {
+    expect(joinURL('https://api.example.com/v1', '/users')).toBe(
+      'https://api.example.com/v1/users',
+    );
+  });
+
+  it('does not double slashes', () => {
+    expect(joinURL('https://api.example.com/v1/', '/users')).toBe(
+      'https://api.example.com/v1/users',
+    );
+  });
+
+  it('adds a slash when neither side has one', () => {
+    expect(joinURL('https://api.example.com/v1', 'users')).toBe(
+      'https://api.example.com/v1/users',
+    );
+  });
+
+  it('returns base when path is empty', () => {
+    expect(joinURL('https://api.example.com', '')).toBe('https://api.example.com');
+  });
+
+  it('returns base when path is "/"', () => {
+    expect(joinURL('https://api.example.com', '/')).toBe('https://api.example.com');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// callHooks
+// ---------------------------------------------------------------------------
+
+describe('callHooks', () => {
+  function makeCtx(): FetchContext {
+    return {
+      request: 'https://example.com',
+      options: { headers: new Headers() },
+      response: undefined,
+      error: undefined,
+    } as FetchContext;
+  }
+
+  it('does nothing when hooks is undefined', async () => {
+    await expect(callHooks(makeCtx(), undefined)).resolves.toBeUndefined();
+  });
+
+  it('calls a single hook', async () => {
+    const calls: number[] = [];
+    await callHooks(makeCtx(), () => {
+      calls.push(1);
+    });
+    expect(calls).toEqual([1]);
+  });
+
+  it('calls an array of hooks in order', async () => {
+    const calls: number[] = [];
+    await callHooks(makeCtx(), [
+      () => { calls.push(1); },
+      () => { calls.push(2); },
+      () => { calls.push(3); },
+    ]);
+    expect(calls).toEqual([1, 2, 3]);
+  });
+
+  it('awaits async hooks', async () => {
+    const calls: number[] = [];
+    await callHooks(makeCtx(), [
+      async () => {
+        await Promise.resolve();
+        calls.push(1);
+      },
+      () => {
+        calls.push(2);
+      },
+    ]);
+    expect(calls).toEqual([1, 2]);
+  });
+});
+
+// ---------------------------------------------------------------------------
+// resolveFetchOptions
+// ---------------------------------------------------------------------------
+
+describe('resolveFetchOptions', () => {
+  it('returns an object with a Headers instance', () => {
+    const resolved = resolveFetchOptions('https://example.com', undefined, undefined);
+    expect(resolved.headers).toBeInstanceOf(Headers);
+  });
+
+  it('merges input and default headers (input wins)', () => {
+    const resolved = resolveFetchOptions(
+      'https://example.com',
+      { headers: { 'x-custom': 'input' } },
+      { headers: { 'x-custom': 'default', 'x-default-only': 'yes' } },
+    );
+    expect(resolved.headers.get('x-custom')).toBe('input');
+    expect(resolved.headers.get('x-default-only')).toBe('yes');
+  });
+
+  it('merges query params from defaults and input', () => {
+    const resolved = resolveFetchOptions(
+      'https://example.com',
+      { query: { a: '1' } },
+      { query: { b: '2' } },
+    );
+    expect(resolved.query).toEqual({ a: '1', b: '2' });
+  });
+
+  it('merges params alias into query', () => {
+    const resolved = resolveFetchOptions(
+      'https://example.com',
+      { params: { p: '10' } },
+      undefined,
+    );
+    expect(resolved.query).toEqual({ p: '10' });
+    expect(resolved.params).toEqual({ p: '10' });
+  });
+});

core/fetch/src/utils.ts

@@ -0,0 +1,285 @@
+import type {
+  FetchContext,
+  FetchHook,
+  FetchOptions,
+  FetchRequest,
+  ResolvedFetchOptions,
+  ResponseType,
+} from './types';
+
+// ---------------------------------------------------------------------------
+// V8 optimisation: module-level frozen Sets avoid per-call allocations and
+// allow V8 to treat them as compile-time constants in hidden-class analysis.
+// ---------------------------------------------------------------------------
+
+/** HTTP methods whose requests carry a body */
+// eslint-disable-next-line @typescript-eslint/no-unsafe-assignment
+const PAYLOAD_METHODS: ReadonlySet<string> = /* @__PURE__ */ new Set(['PATCH', 'POST', 'PUT', 'DELETE']);
+
+/** HTTP status codes whose responses never have a body */
+// eslint-disable-next-line @typescript-eslint/no-unsafe-assignment
+export const NULL_BODY_STATUSES: ReadonlySet<number> = /* @__PURE__ */ new Set([101, 204, 205, 304]);
+
+/** Content-types treated as plain text */
+// eslint-disable-next-line @typescript-eslint/no-unsafe-assignment
+const TEXT_CONTENT_TYPES: ReadonlySet<string> = /* @__PURE__ */ new Set([
+  'image/svg',
+  'application/xml',
+  'application/xhtml',
+  'application/html',
+]);
+
+/** V8: pre-compiled at module load — avoids per-call RegExp construction */
+const JSON_CONTENT_TYPE_RE = /^application\/(?:[\w!#$%&*.^`~-]*\+)?json(;.+)?$/i;
+
+// ---------------------------------------------------------------------------
+// Predicate helpers
+// ---------------------------------------------------------------------------
+
+/**
+ * @name isPayloadMethod
+ * @category Fetch
+ * @description Returns true for HTTP methods that carry a request body
+ *
+ * V8: function is monomorphic — always called with an uppercase string.
+ *
+ * @param {string} method - Uppercase HTTP method string
+ * @returns {boolean}
+ *
+ * @since 0.0.1
+ */
+export function isPayloadMethod(method: string): boolean {
+  return PAYLOAD_METHODS.has(method);
+}
+
+/**
+ * @name isJSONSerializable
+ * @category Fetch
+ * @description Returns true when a value can be serialised with JSON.stringify
+ *
+ * V8: typeof checks are ordered from most-common to least-common to maximise
+ * the probability of an early return and keep the IC monomorphic.
+ *
+ * @param {unknown} value - Any value
+ * @returns {boolean}
+ *
+ * @since 0.0.1
+ */
+export function isJSONSerializable(value: unknown): boolean {
+  if (value === undefined) return false;
+
+  const type = typeof value;
+
+  // Fast path — primitives are always serialisable
+  if (type === 'string' || type === 'number' || type === 'boolean' || value === null) return true;
+
+  // Non-object types (bigint, function, symbol) are not serialisable
+  if (type !== 'object') return false;
+
+  // Arrays are serialisable
+  if (Array.isArray(value)) return true;
+
+  // TypedArrays / ArrayBuffers carry a .buffer property — not JSON-serialisable
+  if ((value as Record<string, unknown>).buffer !== undefined) return false;
+
+  // FormData and URLSearchParams should not be auto-serialised
+  if (value instanceof FormData || value instanceof URLSearchParams) return false;
+
+  // Plain objects or objects with a custom toJSON
+  const ctor = (value as object).constructor;
+  return (
+    ctor === undefined
+    || ctor === Object
+    || typeof (value as Record<string, unknown>).toJSON === 'function'
+  );
+}
+
+// ---------------------------------------------------------------------------
+// Response type detection
+// ---------------------------------------------------------------------------
+
+/**
+ * @name detectResponseType
+ * @category Fetch
+ * @description Infers the response body parsing strategy from a Content-Type header value
+ *
+ * @param {string} [contentType] - Value of the Content-Type response header
+ * @returns {ResponseType}
+ *
+ * @since 0.0.1
+ */
+export function detectResponseType(contentType = ''): ResponseType {
+  if (!contentType) return 'json';
+
+  // V8: split once and reuse — avoids calling split multiple times
+  const type = contentType.split(';')[0] ?? '';
+
+  if (JSON_CONTENT_TYPE_RE.test(type)) return 'json';
+  if (type === 'text/event-stream') return 'stream';
+  if (TEXT_CONTENT_TYPES.has(type) || type.startsWith('text/')) return 'text';
+
+  return 'blob';
+}
+
+// ---------------------------------------------------------------------------
+// URL helpers
+// ---------------------------------------------------------------------------
+
+/**
+ * @name buildURL
+ * @category Fetch
+ * @description Appends serialised query parameters to a URL string
+ *
+ * Null and undefined values are omitted. Existing query strings are preserved.
+ *
+ * @param {string} url - Base URL (may already contain a query string)
+ * @param {Record<string, string | number | boolean | null | undefined>} query - Parameters to append
+ * @returns {string} URL with query string
+ *
+ * @since 0.0.1
+ */
+export function buildURL(
+  url: string,
+  query: Record<string, string | number | boolean | null | undefined>,
+): string {
+  const params = new URLSearchParams();
+
+  for (const key of Object.keys(query)) {
+    const value = query[key];
+    if (value !== null && value !== undefined) {
+      params.append(key, String(value));
+    }
+  }
+
+  const qs = params.toString();
+  if (!qs) return url;
+
+  return url.includes('?') ? `${url}&${qs}` : `${url}?${qs}`;
+}
+
+/**
+ * @name joinURL
+ * @category Fetch
+ * @description Joins a base URL with a relative path, normalising the slash boundary
+ *
+ * @param {string} base - Base URL (e.g. "https://api.example.com/v1")
+ * @param {string} path - Relative path (e.g. "/users")
+ * @returns {string} Joined URL
+ *
+ * @since 0.0.1
+ */
+export function joinURL(base: string, path: string): string {
+  if (!path || path === '/') return base;
+
+  const baseEnds = base.endsWith('/');
+  const pathStarts = path.startsWith('/');
+
+  if (baseEnds && pathStarts) return `${base}${path.slice(1)}`;
+  if (!baseEnds && !pathStarts) return `${base}/${path}`;
+  return `${base}${path}`;
+}
+
+// ---------------------------------------------------------------------------
+// Options resolution
+// ---------------------------------------------------------------------------
+
+/**
+ * @name resolveFetchOptions
+ * @category Fetch
+ * @description Merges per-request options with global defaults
+ *
+ * V8: the returned object always has the same property set (fixed shape),
+ * which lets V8 reuse its hidden class across all calls.
+ *
+ * @since 0.0.1
+ */
+export function resolveFetchOptions<R extends ResponseType = 'json', T = unknown>(
+  request: FetchRequest,
+  input: FetchOptions<R, T> | undefined,
+  defaults: FetchOptions<R, T> | undefined,
+): ResolvedFetchOptions<R, T> {
+  const headers = mergeHeaders(
+    input?.headers ?? (request as Request)?.headers,
+    defaults?.headers,
+  );
+
+  let query: Record<string, string | number | boolean | null | undefined> | undefined;
+  if (
+    defaults?.query !== undefined
+    || defaults?.params !== undefined
+    || input?.params !== undefined
+    || input?.query !== undefined
+  ) {
+    query = {
+      ...defaults?.params,
+      ...defaults?.query,
+      ...input?.params,
+      ...input?.query,
+    };
+  }
+
+  return {
+    ...defaults,
+    ...input,
+    query,
+    params: query,
+    headers,
+  };
+}
+
+/**
+ * Merge two HeadersInit sources into a single Headers instance.
+ * Input headers override default headers.
+ *
+ * V8: avoids constructing an intermediate Headers when defaults are absent.
+ */
+function mergeHeaders(
+  input: HeadersInit | undefined,
+  defaults: HeadersInit | undefined,
+): Headers {
+  if (defaults === undefined) {
+    return new Headers(input);
+  }
+
+  const merged = new Headers(defaults);
+
+  if (input !== undefined) {
+    const src = input instanceof Headers ? input : new Headers(input);
+    for (const [key, value] of src) {
+      merged.set(key, value);
+    }
+  }
+
+  return merged;
+}
+
+// ---------------------------------------------------------------------------
+// Hook dispatch
+// ---------------------------------------------------------------------------
+
+/**
+ * @name callHooks
+ * @category Fetch
+ * @description Invokes one or more lifecycle hooks with the given context
+ *
+ * V8: the single-hook path avoids Array creation; the Array path uses a
+ * for-loop with a cached length to stay monomorphic inside the loop body.
+ *
+ * @since 0.0.1
+ */
+export async function callHooks<C extends FetchContext = FetchContext>(
+  context: C,
+  hooks: FetchHook<C> | readonly FetchHook<C>[] | undefined,
+): Promise<void> {
+  if (hooks === undefined) return;
+
+  if (Array.isArray(hooks)) {
+    const len = hooks.length;
+    for (let i = 0; i < len; i++) {
+      await (hooks as Array<FetchHook<C>>)[i]!(context);
+    }
+  }
+  else {
+    await (hooks as FetchHook<C>)(context);
+  }
+}

core/fetch/tsconfig.json

@@ -0,0 +1,3 @@
+{
+  "extends": "@robonen/tsconfig/tsconfig.json"
+}

core/fetch/tsdown.config.ts

@@ -0,0 +1,7 @@
+import { defineConfig } from 'tsdown';
+import { sharedConfig } from '@robonen/tsdown';
+
+export default defineConfig({
+  ...sharedConfig,
+  entry: ['src/index.ts'],
+});

core/fetch/vitest.config.ts

@@ -0,0 +1,7 @@
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+  test: {
+    environment: 'node',
+  },
+});

pnpm-lock.yaml

@@ -122,6 +122,27 @@ importers:
         specifier: 'catalog:'
         version: 0.21.0(typescript@5.8.3)(vue-tsc@3.2.5(typescript@5.8.3))
 
+  core/fetch:
+    devDependencies:
+      '@robonen/oxlint':
+        specifier: workspace:*
+        version: link:../../configs/oxlint
+      '@robonen/tsconfig':
+        specifier: workspace:*
+        version: link:../../configs/tsconfig
+      '@robonen/tsdown':
+        specifier: workspace:*
+        version: link:../../configs/tsdown
+      '@stylistic/eslint-plugin':
+        specifier: 'catalog:'
+        version: 5.10.0(eslint@10.0.3(jiti@2.6.1))
+      oxlint:
+        specifier: 'catalog:'
+        version: 1.51.0
+      tsdown:
+        specifier: 'catalog:'
+        version: 0.21.0(typescript@5.8.3)(vue-tsc@3.2.5(typescript@5.8.3))
+
   core/platform:
     devDependencies:
       '@robonen/oxlint':

vitest.config.ts

@@ -4,6 +4,7 @@ export default defineConfig({
   test: {
     projects: [
       'configs/oxlint/vitest.config.ts',
+      'core/fetch/vitest.config.ts',
       'core/stdlib/vitest.config.ts',
       'core/platform/vitest.config.ts',
       'vue/toolkit/vitest.config.ts',