Accelerate JS/TS Development with Bun

Bun installs via brew install oven-sh/bun/bun, the official install script from bun.sh, or npm install -g bun, and updates in place with bun upgrade. Its value over Node.js: faster startup (~25ms vs Node's ~100ms+), 10-100x faster package installs, native TypeScript and JSX support with no separate transpiler, and a built-in test runner and bundler where Node relies on external tools (Jest/Vitest, Webpack/esbuild). This skill covers Bun as a JavaScript/TypeScript runtime end to end. Project setup runs TypeScript directly with no build step, initializes new projects (package.json, tsconfig.json, index.ts, README) with optional templates, and manages packages with bun install/bun add/bun remove/bun update, bunx as an npx equivalent that can run a package binary without installing it, and a fast binary bun.lockb lockfile (with a text-lockfile export for debugging, or trusting an existing lockfile). Running code covers direct TypeScript/JavaScript execution, package.json scripts, watch mode with auto-restart or hot reload, automatic .env file loading with variables exposed via Bun.env (or the Node-compatible process.env), and running with a specific env file via --env-file.

Built-in APIs replace common Node.js dependencies: Bun.file()/Bun.write() read and write files (as text, JSON, or an array buffer, with streaming for large files) faster than the fs/promises equivalent; Bun.serve() runs an HTTP server via a fetch(request) handler returning Response/Response.json(), with an error() handler for uncaught errors; the same Bun.serve() upgrades a request to a WebSocket connection with open/message/close handlers; bun:sqlite's Database class runs SQLite queries with prepared statements (db.prepare(...).run()/.get()/.query(...).all()); and Bun ships built-in password hashing. Testing uses Bun's own test runner (bun test, with file/pattern filtering, watch mode, coverage, and timeouts) with its own matchers and mocking support - no separate test framework needed. Bundling (bun build) compiles for production, and Bun can compile a project to a standalone executable, including cross-compilation and embedded assets.

Migrating from Node.js is largely compatible out of the box - fs, path, crypto, the global process, Buffer, __dirname, and __filename all work unmodified - but require() should become import, require.resolve() becomes import.meta.resolve(), process.hrtime() becomes Bun.nanoseconds(), and setImmediate() becomes queueMicrotask(). Common migration steps: install Bun, delete node_modules/package-lock.json and run bun install, update package.json scripts ("start": "node index.js" to "bun run index.ts", "test": "jest" to "bun test"), and add @types/bun.

Use this when starting a new JS/TS project with Bun, migrating an existing Node.js project to Bun, optimizing development speed, using Bun's built-in bundler or test runner, or troubleshooting Bun-specific issues.

For performance, prefer Bun-native APIs over their Node-compatibility equivalents: Bun.file() over fs/promises, and Bun.serve() over Express/Fastify (claimed 4-10x faster) or a Bun-optimized framework like Elysia; always bundle and minify for production with bun build ./src/index.ts --outdir ./dist --minify --target node rather than shipping unbundled source.

Input is a JS/TS project or a specific development task (install a package, run a server, write a test, migrate from Node). Output is Bun-native code and CLI invocations - bun install, bun run, bun test, bun build - or a working Bun.serve()/bun:sqlite/Bun.file()-based implementation in place of the Node.js equivalent.

Built on Bun's own toolchain: its package manager, bundler, test runner, Bun.file/Bun.write/Bun.serve/bun:sqlite/Bun.password built-in APIs, and compatible with most existing Node.js APIs (fs, path, crypto) and package ecosystem via bun install.

JavaScript/TypeScript developers starting a new project with Bun or migrating an existing Node.js project to it for faster installs, execution, testing, and bundling.

const server = Bun.serve({
  port: 3000,

  fetch(request) {
    const url = new URL(request.url);

    if (url.pathname === "/") {
      return new Response("Hello World!");
    }

    if (url.pathname === "/api/users") {
      return Response.json([
        { id: 1, name: "Alice" },
        { id: 2, name: "Bob" },
      ]);
    }

    return new Response("Not Found", { status: 404 });
  },

  error(error) {
    return new Response(`Error: ${error.message}`, { status: 500 });
  },
});

console.log(`Server running at http://localhost:${server.port}`);