Bun APIs

Reported version: Bun.version is 1.4.4-browser. Labels are explained on the overview.

The Bun global

API	Status	Notes
Bun.serve	🟡 Partial	fetch, routes, WebSockets, streaming. See below.
Bun.file	🟡 Partial	exists, text, json, bytes, arrayBuffer, name. Not a Blob: no size, type, stream, slice, writer, delete.
Bun.write	🟡 Partial	Destination is a path, file: URL, BunFile, Bun.stdout or Bun.stderr (file descriptors aren’t). Accepts strings, BunFile, Blob, Response, ArrayBuffer, typed arrays. Creates parent folders.
Bun.build	🟡 Partial	Bun’s real bundler, as wasm (~10 MB, loaded on first use). Supports entrypoints, outdir, target, format, minify, splitting, sourcemap, naming, publicPath, external, define, conditions, banner, footer, throw. plugins are ignored with a warning; loader, env, packages, drop, compile, root aren’t supported.
Bun.env	✅ Works	Same object as process.env; starts as { NODE_ENV: "development" }. .env files aren’t loaded.
Bun.version	✅ Works	Bun.revision is missing.
Bun.semver	✅ Works	order and satisfies, from Bun’s own semver code.
Bun.sleep	✅ Works	sleepSync is missing.
Bun.nanoseconds	✅ Works	Browser clock resolution.
Bun.inspect, Bun.deepEquals, Bun.escapeHTML	✅ Works	inspect is node:util’s, without colors.
Bun.main, Bun.argv	✅ Works	Bun.main is the entry’s path; Bun.argv is ["bun", main], as process.argv.
Bun.stdout, Bun.stderr	🟡 Partial	Work as Bun.write destinations and print to the console. No writer().
Bun.which	⚪ Stub	Returns null: there are no executables.
Bun.gc	⚪ Stub	Does nothing.
Bun.spawn, Bun.spawnSync, Bun.$	❌ Missing	No processes in the browser.
Bun.CryptoHasher	✅ Works	md5, ripemd160, sha1, sha2, sha3, blake2; HMAC with a key; copy, static hash. No md4 or shake.
Bun.password, Bun.hash	❌ Missing	Use Bun.CryptoHasher, node:crypto or crypto.subtle.
Bun.Glob, Bun.Transpiler	❌ Missing
Bun.resolveSync, Bun.stdin	❌ Missing
Bun.sql, Bun.redis, Bun.s3	❌ Missing
Bun.connect, Bun.listen, Bun.udpSocket, Bun.dns	❌ Missing	No raw sockets in the browser.
Bun.gzipSync, Bun.deflateSync, Bun.zstd*	❌ Missing
Bun.CookieMap, Bun.YAML, Bun.TOML, Bun.plugin, Bun.FileSystemRouter, Bun.mmap	❌ Missing
HTMLRewriter	❌ Missing

Bun.serve

Servers answer requests from the preview, not from the network.

Feature	Status	Notes
fetch(req, server)	✅ Works
routes	✅ Works	Exact paths, :param (in req.params), trailing *, per-method handlers, static Responses. Globs in the middle of a path (/a/*/b) don’t match.
HTML imports in routes	✅ Works	import page from "./index.html" is bundled with Bun’s bundler. Assets are served under /_bun/. Rebuilt after any file change. No HMR.
WebSockets	✅ Works	server.upgrade(req, { data }), open/message/close/drain, send, publish, subscribe, cork, close. ping/pong do nothing. Only the preview page can connect.
server.publish, subscriberCount, pendingWebSockets	✅ Works
server.reload, server.stop	✅ Works
server.url, port, hostname	✅ Works	port: 0 picks a port from 40001.
export default { fetch }	✅ Works	Served automatically, as in Bun (Hono, Elysia).
Streaming responses, Server-Sent Events	✅ Works
Cookies	✅ Works	Kept in a cookie jar on the page. cookies in the console lists them.
TLS	❌ Missing
error, idleTimeout, maxRequestBodySize, unix, reusePort	❌ Missing	A throwing handler returns a plain-text 500.
server.requestIP, server.timeout, server.ref/unref	❌ Missing

bun:* modules

Module	Status	Notes
bun:sqlite	🟡 Partial	Built on sql.js. Database with query, prepare, run, transaction, serialize, close; statements with all, get, values, run, iterate. File databases are saved to the project. Missing: Statement.as(), Database.deserialize, loadExtension, safeIntegers, SQLiteError.
bun:test	🟡 Partial	Run with bun test in the console. See below.
bun:ffi, bun:jsc	❌ Missing
bun	✅ Works	import { serve } from "bun" and the default export are the Bun global.

bun:test

• ✅ test/it/describe with .skip, .only, .todo, .each, .if, .skipIf, .todoIf
• ✅ beforeAll, beforeEach, afterEach, afterAll, setDefaultTimeout
• ✅ mock(), spyOn(), jest.fn, jest.spyOn
• ✅ expect with .not, .resolves, .rejects, asymmetric matchers (anything, any, objectContaining, arrayContaining, stringContaining, stringMatching) and the common matchers (toBe, toEqual, toStrictEqual, toThrow, toMatchObject, toHaveProperty, toHaveBeenCalledWith, …), plus Bun’s extras (toBeEmpty, toBeOneOf, toSatisfy, toStartWith, toEndWith, toInclude, toBeArray, toBeString, toBeNumber, toBeFunction, toHaveReturned*, …)
• ❌ Snapshots, fake timers, setSystemTime, mock.module, jest.mock, expect.extend, expect.assertions, coverage, test.concurrent, test.failing
• Unknown matchers throw “is not supported here”.
• bun test takes name filters but no flags.

import.meta and globals

API	Status	Notes
import.meta.url, dirname, filename	✅ Works	file:///<path> in the project.
import.meta.require	🟡 Partial	String literals only (import.meta.require("x")).
import.meta.dir, file, path, main, env	✅ Works	env is process.env. In browser code (HTML imports), only url, dirname and filename are filled in.
import.meta.resolve	❌ Missing	The browser’s own returns the served URL, not a project path.
import(expr) with a computed path	✅ Works
fetch("file:///…")	✅ Works	Reads project files. Relative URLs throw. Other URLs go to the network, subject to CORS.
process, Buffer, global, timers	✅ Works	See Node built-ins.