principletypescriptTip
Bun runtime speed: why Bun starts and runs faster than Node.js
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bun speedJavaScriptCorestartup timeperformanceZigbun vs node
bun
Problem
Understanding why Bun is significantly faster than Node.js for many workloads and when the speed difference matters.
Solution
Bun uses JavaScriptCore (Safari's engine, faster cold starts) instead of V8. It is written in Zig for low overhead. Built-in SQLite, fetch, WebSocket, and file I/O avoid module loading overhead. Startup is roughly 10x faster than Node for small scripts.
Why
Node.js loads dozens of built-in modules at startup. Bun's tight integration of standard library functions in native code skips that overhead entirely.
Gotchas
- Bun is fastest for startup-sensitive tasks (CLIs, scripts); long-running servers see smaller differences
- JavaScriptCore vs V8 may behave differently in edge cases — test thoroughly before migrating
- Node.js compatibility is approximately 95% but some modules may fail; check the Bun compatibility page
- Bun on Linux is generally faster than on macOS due to Linux I/O primitives
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