Bun

What is it?

All-in-one JavaScript/TypeScript runtime written in Zig, powered by JavaScriptCore. Ships as a single executable containing runtime, package manager, bundler, and test runner. Drop-in replacement for Node.js.

What is it for?

• High-performance APIs and HTTP servers
• Serverless functions requiring fast cold starts
• TypeScript services with native .ts execution (no transpile step)
• Development tooling (faster package installation, testing)

Why was it chosen?

Key advantages:

• Fastest JavaScript runtime available
• Native TypeScript without build step
• Built-in tooling reduces dependency count
• High Node.js compatibility for easy migration

Note: For database-bound workloads, performance difference is negligible (~5%). Runtime choice matters most for compute-heavy or I/O-heavy operations.

Known limitations

Node.js API gaps:

• node:http2 server not implemented (client only)
• node:cluster limited (workers cannot pass handles)
• node:inspector, node:repl, node:sqlite missing
• Partial: worker_threads, vm, crypto, child_process

SvelteKit-specific:

• svelte-adapter-bun is community-maintained (not official SvelteKit adapter)
• Known issues with CORS and form handling (ORIGIN header not passed correctly)
• Vite dev server still runs on Node.js (only production uses Bun)
• Easy fallback: switch to adapter-node with single config change

Production considerations:

• Third-party observability tools have limited support
• Packages relying on Node internals may fail
• Enterprise adoption remains cautious vs Node.js maturity

Mitigation: Anthropic acquired Bun (December 2024), providing long-term sustainability. Bun remains MIT-licensed and open-source.

Related

• sveltekit.md - Framework integration
• podman.md - Container setup
• ../ops/deployment.md - Deployment targets