| name | bun-runtime |
| description | Bun as runtime, package manager, bundler, and test runner. When to choose Bun vs Node, migration notes, and Vercel support. |
| metadata | {"origin":"ECC"} |
Bun Runtime
Bun is a fast all-in-one JavaScript runtime and toolkit: runtime, package manager, bundler, and test runner.
When to Use
- Prefer Bun for: new JS/TS projects, scripts where install/run speed matters, Vercel deployments with Bun runtime, and when you want a single toolchain (run + install + test + build).
- Prefer Node for: maximum ecosystem compatibility, legacy tooling that assumes Node, or when a dependency has known Bun issues.
Use when: adopting Bun, migrating from Node, writing or debugging Bun scripts/tests, or configuring Bun on Vercel or other platforms.
How It Works
- Runtime: Drop-in Node-compatible runtime, powered by JavaScriptCore. Originally implemented in Zig; rewritten in Rust in mid-2026 (still JavaScriptCore-based — the engine swap doesn't change any of the usage below).
- Package manager:
bun install is significantly faster than npm/yarn. Lockfile is bun.lock (text) by default in current Bun; older versions used bun.lockb (binary).
- Bundler: Built-in bundler and transpiler for apps and libraries.
- Test runner: Built-in
bun test with Jest-like API.
Migration from Node: Replace node script.js with bun run script.js or bun script.js. Run in place of ; most packages work. Use for npm scripts; for npx-style one-off runs. Node built-ins are supported; prefer Bun APIs where they exist for better performance.