Node.js vs Bun: Key Runtime Differences That Actually Affect Your Backend

Node.js and Bun both execute JavaScript and TypeScript backends, but they differ significantly in their underlying engines — Node.js uses Google's V8, while Bun is built on JavaScriptCore from WebKit. One of Bun's most notable features is native TypeScript execution without additional tooling, though developers are advised to retain the TypeScript compiler for static type checking. The two runtimes also diverge in their HTTP server APIs, with Node.js relying on its own IncomingMessage and ServerResponse objects, while Bun adopts standard Web APIs such as Request, Response, and fetch. Beyond raw performance benchmarks, practical differences emerge across areas like module resolution, WebSockets, streams, workers, and Docker compatibility. Switching runtimes is therefore less about choosing a faster JavaScript engine and more about adopting an entirely different ecosystem of APIs and tooling.