Bun – fast JavaScript runtime

Bun is an all-in-one JavaScript runtime and toolkit designed for speed, complete with a bundler, test runner, and Node.js-compatible package manager. It ships as a single executable called bun.

At its core is the Bun runtime, a fast JavaScript runtime designed as a drop-in replacement for Node.js. It’s written in Zig and powered by JavaScriptCore under the hood, dramatically reducing startup times and memory usage.

This is free and open source software.

Features include:

  • Node.js compatibility – aims for complete Node.js API compatibility. Most npm packages intended for Node.js environments will work with Bun out of the box.
  • Extends the JavaScriptCore engine—the performance-minded JS engine built for Safari—with native-speed functionality implemented in Zig.
  • Consistent and predictable module resolution system that just works.
  • Supports .jsx and .tsx files out of the box. Bun’s internal transpiler converts JSX syntax into vanilla JavaScript before execution.
  • Treats TypeScript as a first-class citizen.
  • Supports two kinds of automatic reloading via CLI flags.
  • Contains a Node.js-compatible package manager designed to be a dramatically faster replacement for npm, yarn, and pnpm. It’s a standalone tool that will work in pre-existing Node.js projects.
  • Implements Web-standard APIs such as fetch, ReadableStream, Request, Response, WebSocket, and FormData.
  • Cross-platform bash-like shell with seamless JavaScript interop:
    • Use Bun Shell without installing extra dependencies. Common shell commands like ls, cd, rm are implemented natively.
    • Familiar: Bun Shell is a bash-like shell, supporting redirection, pipes, environment variables and more.
    • Globs: Glob patterns are supported natively, including **, *, {expansion}, and more.
    • Template literals: Template literals are used to execute shell commands. This allows for easy interpolation of variables and expressions.
    • Safety: Bun Shell escapes all strings by default, preventing shell injection attacks.
    • JavaScript interop: Use Response, ArrayBuffer, Blob, Bun.file(path) and other JavaScript objects as stdin, stdout, and stderr.
    • Shell scripting: Bun Shell can be used to run shell scripts ( files).
    • Custom interpreter: Bun Shell is written in Zig, along with it’s lexer, parser, and interpreter. Bun Shell is a small programming language.

Support: GitHub Code Repository
Developer: Bun Team
License: MIT License

Bun is written in Zig and C++. Learn Zig with our recommended free tutorials. Learn C++ with our recommended free books and free tutorials.

Return to JavaScript Runtime Environments

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