What you'll learn
Quick Answer
Node.js is the JavaScript runtime that has run servers for over a decade, built on Google's V8 engine. Bun is a newer runtime built on Apple's JavaScriptCore that also ships a test runner, bundler, and package manager in the same binary, and runs TypeScript and JSX directly. Bun aims to be a drop-in replacement for Node, but its Node compatibility is still an ongoing effort, so many mature production systems stay on Node.
What Bun actually is
Bun's own documentation describes four integrated tools in one binary: a runtime, a package manager (bun install), a test runner, and a bundler. It is written in Zig and powered by JavaScriptCore, the engine from Safari and WebKit, rather than the V8 engine Node uses.
Node is the runtime alone. Everything else in a typical Node project comes from separate packages that you pick, wire together, and upgrade independently: Jest or Vitest for tests, esbuild or webpack or Rollup for bundling, npm or pnpm or yarn for dependencies.
That is the real distinction, and it matters more than raw speed. Node is a runtime you assemble a toolchain around; Bun is a toolchain with the runtime included. The engine swap has consequences too, since a handful of libraries depend on V8-specific behaviour or APIs. On the machine used to check this article, bun --version reported 1.4.2.
TypeScript with no build step
Bun executes .ts, .tsx, and .jsx files directly; its transpiler converts them to JavaScript in memory before execution. Running a typed file here needed no configuration and no tsconfig: bun run demo.ts simply ran.
Node has partly caught up. Type stripping runs without a flag from Node 22.18 and 23.6, and is stable in Node 24. But Node only removes erasable syntax, meaning type annotations that leave no runtime trace. On the Node 22.16 used here, running a .ts file directly failed with a syntax error until --experimental-strip-types was added. Even with the flag, a file containing a TypeScript enum failed with ERR_UNSUPPORTED_TYPESCRIPT_SYNTAX: TypeScript enum is not supported in strip-only mode.
Bun ran the exact same enum file and printed the expected output. Namespaces with runtime code and constructor parameter properties fall in the same category: Node needs a further --experimental-transform-types flag, while Bun handles them out of the box.
One caveat applies to both: running a file is not type-checking it. Neither Bun nor Node reports type errors at runtime; they strip or transform the types and execute. You still run tsc --noEmit, or your editor, to actually catch mistakes.
The built-in toolchain
Each of Bun's bundled tools was exercised for this article, and each replaces something you would otherwise install and configure:
bun testis a Jest-compatible runner. A file importingbun:testran two tests, reporting2 pass, 0 failin about 43 milliseconds, with no test framework added to the project.bun buildbundled a module for a Node target in a single command, no config file.bun installresolved and installed packages intonode_modulesand wrote a text lockfile,bun.lock. Bun's documentation claims installs up to 30 times faster than npm.
On Node, matching that means choosing and maintaining Vitest or Jest, esbuild or tsup, and staying on npm or a third-party alternative. None of it is difficult individually, but it is a stack of decisions, config files, and version bumps that Bun collapses into one tool with one version number. The runner also reads tsconfig.json paths and runs .test.ts files with no transform step, so there is no ts-jest-style layer to configure or keep in sync.
Node compatibility and Web APIs
Bun implements Node globals such as process and Buffer, built-in modules such as path, fs, and http, and Web-standard APIs including fetch, WebSocket, ReadableStream, Headers, and URL. Modern Node exposes a global fetch as well, so that particular gap has closed on both sides.
Bun's documentation still calls Node compatibility an ongoing effort. Native addons compiled against Node's ABI, some edge cases inside node: modules, and libraries that reach directly into V8 or Node internals can still break under Bun.
The gotcha is that you cannot predict which package will be the problem. A dependency that has run on Node for years might hit a compatibility gap the first time you run it under Bun, often deep in a transitive dependency you have never looked at. Run your actual dependency tree and your real test suite under Bun before you commit to it, rather than trusting the drop-in promise.
Which to pick
Reach for Bun on new projects, one-off scripts, monorepo tooling, and CI pipelines, where the all-in-one toolchain and TypeScript-first workflow remove setup work and the faster installs add up across hundreds of runs.
Stay on Node for existing production systems that already work, anything depending on native addons or Node-specific internals, and platforms or hosting providers that only certify and support Node releases.
The two also coexist well, and many teams run that way deliberately: Bun as the package manager and test runner during development for the speed, with the service still built and deployed on Node for the stability and support guarantees. The advice that holds up is narrow. Do not rewrite a working service just to change the runtime underneath it, since the upside is marginal and the regression risk is real. Do consider Bun seriously when you are starting something new and the toolchain consolidation, the native TypeScript, and the faster CI are worth the smaller compatibility risk.