Definition
Bun is a fast, all-in-one JavaScript and TypeScript runtime, bundler, package manager, and test runner designed as a drop-in alternative to Node.js.
Overview
Unlike Node.js, which is built on Google's V8 engine, Bun is built on JavaScriptCore (the engine behind Safari) and implemented in the Zig programming language, which its creators cite as a key reason for its faster startup times and package installation speed. Bun aims for broad compatibility with existing Node.js APIs and the npm registry, so many existing projects can switch to Bun as a runtime with minimal changes. Created by Jarred Sumner and first released in 2022, Bun reached its 1.0 milestone in September 2023 and has continued expanding Node.js API compatibility since. Beyond just running JavaScript and TypeScript directly without a separate build step, Bun bundles a package manager (a faster alternative to Yarn or npm), a bundler comparable in purpose to Vite, and a built-in test runner, consolidating tools that are traditionally separate packages in the JavaScript ecosystem.
Key Features
- Built on JavaScriptCore instead of V8 for faster startup
- Native TypeScript and JSX support without extra configuration
- Built-in package manager (bun install) compatible with the npm registry
- Built-in bundler and test runner
- Node.js API compatibility layer for easier migration
- Native SQLite and several Web APIs supported out of the box
- Written in Zig for performance-focused internals