Bun Runtime

Bun is a Node-compatible JS runtime, package manager, bundler, and test runner — all one binary, written in Zig. Faster than Node + pnpm + tsc + vitest combined for most workloads. Trade-off: 95% Node compatibility, not 100%.

When to use

• New TS/JS project — install speed alone is worth it.
• Build/test bottleneck on your CI.
• Edge-deploy compatible (Cloudflare Workers / Vercel) — Bun runs on Vercel as of 2025.
• CLI tools — bun build --compile produces single-binary executables.

When NOT to use

• Production runtime for a Node app with deep ecosystem deps you haven't tested.
• Apps using native modules that haven't been ported (rare; check your node_modules).
• Any case where "must be 100% Node identical" is a hard requirement.

What Bun replaces