Bun 1.0 is here! Read the announcement →

Bun v1.0.15 is now available →

Bun is a fast JavaScript
all-in-one toolkit|

Develop, test, run, and bundle JavaScript & TypeScript projects—all with Bun. Bun is an all-in-one JavaScript runtime & toolkit designed for speed, complete with a bundler, test runner, and Node.js-compatible package manager.

Install Bun v1.0.15

curl -fsSL https://bun.sh/install | bash

Supported on macOS, Linux, and WSL

$ bun run

Bun is a JavaScript runtime.

Bun is a new JavaScript runtime built from scratch to serve the modern JavaScript ecosystem. It has three major design goals:

Speed. Bun starts fast and runs fast. It extends JavaScriptCore, the performance-minded JS engine built for Safari. As computing moves to the edge, this is critical.
Elegant APIs. Bun provides a minimal set of highly-optimimized APIs for performing common tasks, like starting an HTTP server and writing files.
Cohesive DX. Bun is a complete toolkit for building JavaScript apps, including a package manager, test runner, and bundler.

Bun is designed as a drop-in replacement for Node.js. It natively implements hundreds of Node.js and Web APIs, including fs, path, Buffer and more.

The goal of Bun is to run most of the world's server-side JavaScript and provide tools to improve performance, reduce complexity, and multiply developer productivity.

Drop-in Node.js compatibility

Bun aims to be a drop-in replacement for Node.js. It implements Node's module resolution algorithm, globals like Buffer and process, and built-in modules like fs and path. Click to track Bun's progress towards full compatibility.

Fast running performance

Bun extends the JavaScriptCore engine—the performance-minded JS engine built for Safari—with native-speed functionality implemented in Zig.

Works with node_modules

With Bun, you still use package.json to manage your dependencies. Use Bun's native npm client to see just how fast installing dependencies can be.

No more module madness

Forget the complicated rules around CommonJS, ESM, file extensions, resolution priority, and package.json configurations. With Bun, it just works.

TypeScript

TypeScript is a first-class citizen in Bun. Directly execute .ts and .tsx files. Bun respects your settings configured in tsconfig.json, including "paths", "jsx", and more.

Web-standard APIs

Bun implements the Web-standard APIs you know and love, including fetch, ReadableStream, Request, Response, WebSocket, and FormData.

JSX

JSX just works. Bun internally transpiles JSX syntax to vanilla JavaScript. Like TypeScript itself, Bun assumes React by default but respects custom JSX transforms defined in tsconfig.json.

Watch mode

The bun run CLI provides a smart --watch flag that automatically restarts the process when any imported file changes.

The APIs you need. Baked in.

Start an HTTP server

Start a WebSocket server

Read and write files

Hash a password

Bundle for the browser

Write a test

File system routing

Read a stream

Spawn a child process

Call a C function

index.tsx
const server = Bun.serve({
  port: 3000,
  fetch(request) {
    return new Response("Welcome to Bun!");
  },
});

console.log(`Listening on localhost:${server.port}`);

index.tsx
const server = Bun.serve<{ authToken: string; }>({
  fetch(req, server) {
    // use a library to parse cookies
    const cookies = parseCookies(req.headers.get("Cookie"));
    server.upgrade(req, {
      data: { authToken: cookies['X-Token'] },
    });
  },
  websocket: {
    // handler called when a message is received
    async message(ws, message) {
      console.log(`Received: ${message}`);
      const user = getUserFromToken(ws.data.authToken);
      await db.Message.insert({
        message: String(message),
        userId: user.id,
      });
    },
  },
});

console.log(`Listening on localhost:${server.port}`);

index.tsx
const file = Bun.file(import.meta.dir + '/package.json'); // BunFile

const pkg = await file.json(); // BunFile extends Blob
pkg.name = 'my-package';
pkg.version = '1.0.0';

await Bun.write(file, JSON.stringify(pkg, null, 2));

index.tsx
const password = "super-secure-pa$$word";

const hash = await Bun.password.hash(password);
// => $argon2id$v=19$m=65536,t=2,p=1$tFq+9AVr1bfPxQdh...

const isMatch = await Bun.password.verify(password, hash);
// => true

bundle.tsx
await Bun.build({
  entrypoints: ["./index.tsx"],
  outdir: "./build",
  minify: true,
  plugins: [ /* ... */ ]
})

index.tsx
import { describe, expect, test, beforeAll } from "bun:test";

beforeAll(() => {
  // setup tests
});

describe("math", () => {
  test("addition", () => {
    expect(2 + 2).toBe(4);
    expect(7 + 13).toMatchSnapshot();
  });
});

index.tsx
const router = new Bun.FileSystemRouter({
  style: "nextjs",
  dir: "/path/to/pages"
});

const match = router.match("/blog/my-cool-post");
match.filePath; // "/path/to/pages/blog/[slug].tsx",
match.kind; // "dynamic"
match.params; // { slug: "my-cool-post" }

index.tsx
const response = await fetch("https://bun.sh");

await Bun.readableStreamToArrayBuffer(response.body); // => ArrayBuffer
await Bun.readableStreamToBlob(response.body); // => Blob
await Bun.readableStreamToJSON(response.body); // => object
await Bun.readableStreamToText(response.body); // => string
await Bun.readableStreamToArray(response.body); // => unknown[]

index.tsx
const proc = Bun.spawn(["echo", "hello"], {
  cwd: "./path/to/subdir", // specify a working direcory
  env: { ...process.env, FOO: "bar" }, // specify environment variables
  onExit(proc, exitCode, signalCode, error) {
    // exit handler
  },
});

const text = await new Response(proc.stdout).text();
console.log(text); // => "hello"

index.tsx
import { dlopen, FFIType, suffix } from "bun:ffi";

// `suffix` is either "dylib", "so", or "dll" depending on the platform
const path = `libsqlite3.${suffix}`;

const {
  symbols: {
    sqlite3_libversion, // the function to call
  },
} = dlopen(path, {
  sqlite3_libversion: {
    args: [], // no arguments
    returns: FFIType.cstring, // returns a string
  },
});

console.log(`SQLite 3 version: ${sqlite3_libversion()}`);

$ bun install

Bun is an npm-compatible package manager.

Bun

pnpm

17x slower

npm

29x slower

Yarn

33x slower

Installing dependencies from cache for a Remix app.
View benchmark

Node.js compatible

Bun still installs your dependencies into node_modules like npm and other package managers—it just does it faster. You don't need to use the Bun runtime to use Bun as a package manager.

Crazy fast

Bun uses the fastest system calls available on each operating system to make installs faster than you'd think possible.

Workspaces

Workspaces are supported out of the box. Bun reads the workspaces key from your package.json and installs dependencies for your whole monorepo.

Global install cache

Download once, install anywhere. Bun only downloads a particular version of a package from npm once; future installations will copy it from the cache.

Binary lockfile

After installation, Bun creates a binary bun.lockb lockfile with the resolved versions of each dependency. The binary format makes reading and parsing much faster than JSON- or Yaml-based lockfiles.

Familiar API

Bun's CLI uses commands and flags that will feel familiar to any users of npm, pnpm, or yarn.

Replace yarn with bun install to get 30x faster package installs.

$ bun test

Bun is a test runner that makes the rest look like test walkers.

Bun

Vitest

5x slower

Jest+SWC

8x slower

Jest+tsjest

18x slower

Jest+Babel

20x slower

Running the test suite for Zod
View benchmark

Jest-compatible syntax

Bun provides a Jest-style expect() API. Switch to bun test with no code changes.

Crazy fast

Bun's fast startup times shine in the test runner. You won't believe how much faster your tests will run.

Lifecycle hooks

Run setup and teardown code per-test with beforeEach/afterEach or per-file with beforeAll/afterAll.

Snapshot testing

Full support for on-disk snapshot testing with .toMatchSnapshot(). Overwrite snapshots with the --update-snapshots flag.

DOM APIs

Simulate DOM and browser APIs in your tests using happy-dom.

Watch mode

Use the --watch flag to re-run tests when files change using Bun's instantaneous watch mode.

Function mocks

Mock functions with mock() or spy on methods with spyOn().

Replace jest with bun test to run your tests 10-30x faster.

1

Install Bun

curl -fsSL https://bun.sh/install | bash

2

Write your code

index.tsx
const server = Bun.serve({
  port: 3000,
  fetch(request) {
    return new Response("Welcome to Bun!");
  },
});

console.log(`Listening on localhost:${server.port}`);

3

Run the file

bun index.tsx

Learn by example.

Our guides break down how to perform common tasks with Bun.

Ecosystem

Build a frontend using Vite and Bun

Runtime

Install TypeScript declarations for Bun

Streams

Convert a ReadableStream to a string with Bun

HTTP

Hot reload an HTTP server

Write a simple HTTP server

Configure TLS on an HTTP server

Send an HTTP request using fetch

Stream a file as an HTTP Response

Upload files via HTTP using FormData

Package manager

Add a dependency

Add a Git dependency

Add a peer dependency

Add a tarball dependency

Add a trusted dependency

Add an optional dependency

Add a development dependency

Using bun install with Artifactory

Generate a human-readable lockfile

Configuring a monorepo using workspaces

Install a package under a different name

Install dependencies with Bun in GitHub Actions

Override the default npm registry for bun install

Using bun install with an Azure Artifacts npm registry

Configure a private registry for an organization scope with bun install

Processes

Read from stdin

Listen for CTRL+C

Listen to OS signals

Spawn a child process

Parse command-line arguments

Read stderr from a child process

Read stdout from a child process

Get the process uptime in nanoseconds

Spawn a child process and communicate using IPC

Reading files

Read a JSON file

Check if a file exists

Read a file to a Buffer

Read a file as a string

Get the MIME type of a file

Read a file to a Uint8Array

Read a file to an ArrayBuffer

Watch a directory for changes

Read a file as a ReadableStream

Runtime

Import a JSON file

Import a TOML file

Re-map import paths

Set a time zone in Bun

Set environment variables

Read environment variables

Debugging Bun with the web debugger

Install and run Bun in GitHub Actions

Install TypeScript declarations for Bun

Debugging Bun with the VS Code extension

Streams

Convert a ReadableStream to a Blob

Convert a ReadableStream to a JSON

Convert a ReadableStream to a Buffer

Convert a ReadableStream to a string

Convert a ReadableStream to a Uint8Array

Convert a ReadableStream to an ArrayBuffer

Convert a ReadableStream to an array of chunks

Test runner

Mock functions in bun test

Spy on methods in bun test

Update snapshots in bun test

Run tests in watch mode with Bun

Use snapshot testing in bun test

Bail early with the Bun test runner

Skip tests with the Bun test runner

Migrate from Jest to Bun's test runner

Run your tests with the Bun test runner

Set the system time in Bun's test runner

Write browser DOM tests with Bun and happy-dom

Set a per-test timeout with the Bun test runner

Mark a test as a "todo" with the Bun test runner

Re-run tests multiple times with the Bun test runner

Set a code coverage threshold with the Bun test runner

Generate code coverage reports with the Bun test runner

Utilities

Hash a password

Escape an HTML string

Get the current Bun version

Encode and decode base64 strings

Check if two objects are deeply equal

Detect when code is executed with Bun

Get the directory of the current file

Get the file name of the current file

Convert a file URL to an absolute path

Compress and decompress data with gzip

Convert an absolute path to a file URL

Sleep for a fixed number of milliseconds

Compress and decompress data with DEFLATE

Get the absolute path of the current file

Check if the current file is the entrypoint

Get the absolute path to the current entrypoint

WebSocket

Build a simple WebSocket server

Enable compression for WebSocket messages

Build a publish-subscribe WebSocket server

Set per-socket contextual data on a WebSocket

Upgrade an HTTP request to a WebSocket connection

Writing files

Write to stdout

Write a Blob to a file

Write a file to stdout

Append content to a file

Write a string to a file

Write a file incrementally

Write a Response to a file

Copy a file to another location

Write a ReadableStream to a file