Why I Switched to Bun (and When You Might Want To)

I used Node.js for years and still trust it. But for new scripts, APIs, and side projects, I increasingly reach for Bun. The attraction is not one benchmark. It is the fact that the runtime, package manager, bundler, and test runner feel like one product.

That changes the first hour of a project. Instead of choosing and configuring several tools, I can install dependencies, run TypeScript, execute tests, and build from the same command-line interface.

Bun is most compelling when a simpler toolchain matters as much as raw runtime speed.

What Bun actually is

Bun is a JavaScript runtime built around JavaScriptCore. It aims to run much of the same server-side JavaScript as Node.js while also shipping a package manager, test runner, and bundler in a single executable.

TypeScript, TSX, and JSX are handled out of the box. For a small script, that means this is enough:

bun run src/index.ts

There is no separate transpilation command in the basic workflow. For a larger application I still keep a strict tsconfig.json, linting, and explicit build checks. Native TypeScript execution removes setup; it does not replace type checking or engineering discipline.

The all-in-one appeal

Before Bun, a small service might involve Node.js, npm or pnpm, a TypeScript runner, a test runner, and a bundler. Bun can cover each of those jobs:

# Install dependencies
bun install

# Run a TypeScript entry point
bun run src/index.ts

# Execute tests
bun test

# Produce a build
bun build ./src/index.ts --outdir=./dist

This does not mean every project should replace its established toolchain. On a mature product, compatibility and operational confidence usually matter more than shaving a few files from the repository. The benefit is strongest when starting fresh or simplifying a small codebase.

Where it shines

Scripts and command-line tools

Fast startup and direct TypeScript execution suit tools that run frequently and finish quickly. Migration scripts, release helpers, content processors, and small internal utilities are good candidates.

New APIs

Bun includes an HTTP server, so a small endpoint can be written without a framework:

const server = Bun.serve({
  port: 3000,
  fetch(request) {
    const url = new URL(request.url);

    if (url.pathname === "/health") {
      return Response.json({ ok: true });
    }

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

console.log(`Listening on http://localhost:${server.port}`);

For routing, validation, authentication, and middleware, I prefer adding a focused framework instead of growing a homemade abstraction.

Existing Node.js projects

Adoption does not have to be all or nothing. A team can try Bun as a package manager or test runner before changing the production runtime. That smaller experiment makes compatibility problems visible without turning the first trial into a platform migration.

React and JSX

Bun understands JSX and TSX, and its bundler can process React source. That makes it useful for experiments, component demos, and lightweight applications.

import { useState } from "react";

export function Counter() {
  const [count, setCount] = useState(0);

  return (
    <button onClick={() => setCount((value) => value + 1)}>
      Clicks: {count}
    </button>
  );
}

For framework applications, the framework still defines the architecture. Bun can install packages and run scripts, but Next.js, Remix, or another framework remains responsible for routing, rendering, and deployment behavior. That distinction prevents “using Bun” from becoming an unnecessary rewrite.

Hono with Bun

When Bun.serve becomes too manual, Hono is a useful next layer. Its request and response model stays close to web standards, and the same application can target more than one runtime.

bun add hono

import { Hono } from "hono";

const app = new Hono();

app.get("/", (context) => context.text("Hello from Hono + Bun"));
app.get("/api/projects", (context) => {
  return context.json({ projects: [] });
});

Bun.serve({
  port: 3000,
  fetch: app.fetch,
});

The portability is more valuable to me than a synthetic requests-per-second number. It keeps the application code from depending too heavily on one deployment target.

Where I stay cautious

Compatibility

Bun targets Node.js compatibility, but “compatible” is not the same as “identical.” Native addons, uncommon stream behavior, and packages that depend on undocumented Node.js details deserve explicit testing.

Production operations

A runtime decision affects observability, debugging, container images, incident response, and the knowledge already present on a team. For a critical service, I want load tests, failure tests, and a rollback path—not only a successful local run.

Lockfiles and team consistency

Switching package managers changes the lockfile and the commands contributors use. Mixed package managers create noisy diffs and hard-to-reproduce installs. If a team adopts Bun for dependency management, the repository should document that choice and enforce it in CI.

A practical evaluation checklist

Before migrating a real project, I check:

whether install and test times improve meaningfully;
whether all native and build-time dependencies behave correctly;
whether CI and the production host support the chosen Bun version;
whether logs, signals, and shutdown behavior are observable;
whether the team can reproduce the build from a clean clone;
and whether falling back to Node.js remains straightforward.

Wrap-up

Bun is not a requirement for modern JavaScript, and Node.js is not obsolete. Bun earns a place when its integrated workflow makes a project easier to understand and faster to operate.

My default is simple: experiment on a low-risk project, measure the whole workflow, and expand adoption only when the compatibility story is boring. Tooling should remove friction, not become the project.