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Bun runtime: speed advantages, compatibility gaps, and when to adopt
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Bun 1+
bun runtimebun install speedbun vs nodebun testzig javascript
node
Problem
Bun promises dramatically faster installs, test runs, and startup times, but teams adopt it without understanding what Node.js APIs or npm packages may not yet be compatible.
Solution
Bun is a drop-in Node.js runtime for most use cases. Use it where speed matters most; verify compatibility for edge cases.
# Bun is a runtime + bundler + package manager + test runner
bun install # package installation (much faster than npm)
bun run src/index.ts # run TypeScript directly, no transpile step
bun test # Jest-compatible test runner
bun build ./src/index.ts --outdir ./dist # bundler
# Key Bun globals (Node-compatible):
# Bun.file(), Bun.serve(), Bun.sqlite (built-in SQLite)
# Check compatibility before adopting
# Most Node.js built-ins are supported
# Some native addons (.node files) are not
# Some Node.js 'cluster' module APIs are unimplemented
# Bun is a runtime + bundler + package manager + test runner
bun install # package installation (much faster than npm)
bun run src/index.ts # run TypeScript directly, no transpile step
bun test # Jest-compatible test runner
bun build ./src/index.ts --outdir ./dist # bundler
# Key Bun globals (Node-compatible):
# Bun.file(), Bun.serve(), Bun.sqlite (built-in SQLite)
# Check compatibility before adopting
# Most Node.js built-ins are supported
# Some native addons (.node files) are not
# Some Node.js 'cluster' module APIs are unimplemented
Why
Bun is written in Zig and uses JavaScriptCore (Safari's JS engine) instead of V8. Its package install is implemented in native code and uses a binary lockfile format (bun.lockb). These choices yield 3-30x faster installs and 2-4x faster startup vs Node.
Gotchas
- bun.lockb is a binary file — PR diffs are unreadable; use 'bun install --yarn' to also generate yarn.lock for review
- Bun's test runner is Jest-compatible but does not support all Jest matchers or plugins
- Some popular packages with native bindings (sharp, canvas) may need --smol or fallback to Node
- Bun's hot reload (--hot) patches running modules in-place; --watch restarts the process (use the right one)
Context
Evaluating Bun as a replacement for Node.js + npm in development or production
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