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Bun: Fast JavaScript runtime, transpiler, and NPM client written in Zig

Bun: Fast JavaScript runtime, transpiler, and NPM client written in Zig 

Bun is a modern JavaScript runtime like Node or Deno. It was built from scratch to focus on three main things:

  • Start fast (it has the edge in mind).
  • New levels of performance (extending JavaScriptCore, the engine).
  • Being a great and complete tool (bundler, transpiler, package manager).

Bun is designed as a drop-in replacement for your current JavaScript & TypeScript apps or scripts — on your local computer, server or on the edge. Bun natively implements hundreds of Node.js and Web APIs, including ~90% of Node-API functions (native modules), fs, path, Buffer and more.

The goal of Bun is to run most of the worlds JavaScript outside of browsers, bringing performance and complexity enhancements to your future infrastructure, as well as developer productivity through better, simpler tooling.

  • Web APIs like fetch, WebSocket, and ReadableStream are builtin
  • node_modules bun implements Node.js’ module resolution algorithm, so you can use npm packages in bun.js. ESM and CommonJS are supported, but Bun internally uses ESM.
  • In bun.js, every file is transpiled. TypeScript & JSX just work.
  • bun supports "paths", "jsxImportSource"and more from tsconfig.json files
  • Bun.Transpiler bun’s JSX & TypeScript transpiler is available as an API in Bun.js
  • use the fastest system calls available with Bun.write to write, copy, pipe, send and clone files.
  • bun.js automatically loads environment variables from .env files. No more require("dotenv").load()
  • bun ships with a fast SQLite3 client builtin bun:sqlite
  • Node-API bun.js implements most ofNode-API (N-API). Many Node.js native modules just work.
  • bun:ffi call native code from JavaScript with bun’s low-overhead foreign function interface
  • node:fs node:path bun.js natively supports a growing list of Node.js core modules along with globals like Buffer and process.

Bun.js uses the


engine, which tends

to start

and perform a little faster than more traditional choices like V8. Bun is written in

, a low-level programming language with manual memory management.

Most of Bun is written from scratch including the JSX/TypeScript transpiler, npm client, bundler, SQLite client, HTTP client, WebSocket client and more.

An enourmous amount of time spent profiling, benchmarking and optimizing things. The answer is different for every part of Bun, but one general theme: ‘s low-level control over memory and lack of hidden control flow makes it much simpler to write fast software. Sponsor the Zig Software Foundation

To install bun, run this install script in your terminal. It downloads Bun from GitHub.

curl | bash

Bun’s HTTP server is built on web standards like Request and Response

// http.js
export default {
  port: 3000,
  fetch(request) {
    return new Response("Welcome to Bun!");

Run it with bun:

bun run

The same command for running JavaScript & TypeScript files with bun’s JavaScript runtime also runs package.json "scripts".

Replace npm run with bun run and save 160ms on every run.

bun install

bun install is an npm-compatible package manager. You probably will be surprised by how much faster copying files can get.

Replace yarn with bun install and get 20x faster package installs.

bun install uses the fastest system calls available to copy files.

bun wiptest

A Jest-like test runner for JavaScript & TypeScript projects builtin to bun

MIT License, excluding dependencies which have various licenses.

Bun is on GitHub

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