How to Migrate from Node.js to Bun in 30 Minutes
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Let’s be honest: Node.js isn’t going anywhere. It’s stable, battle-tested, and runs half the internet. But Bun? Bun is fast. Not “10% faster” fast—we’re talking 2x to 4x faster in many real-world scenarios. And the best part? You don’t need to rewrite your entire codebase to get there.
In this guide, I’m going to walk you through a real, working migration from Node.js to Bun in about 30 minutes. Not a toy project. A real project with dependencies, environment variables, and a test suite. I’ll show you the gotchas, the hidden traps, and exactly where Bun still stumbles.
Let’s get to it.
Why Bother Migrating to Bun?
Before we touch a terminal, let’s talk about why you’d even consider this. Bun is a JavaScript runtime built from scratch, using JavaScriptCore (the same engine that powers Safari) instead of V8. That alone gives it some interesting performance characteristics. But the real wins come from the integrated toolchain.
Bun isn’t just a runtime—it’s a:
- Package manager (like npm or pnpm)
- Bundler (like webpack or esbuild)
- Test runner (like Jest or Vitest)
- Transpiler (like Babel)
All rolled into one. No more juggling ts-node, tsc, jest, webpack, and npm. One binary does it all. And because it’s written in Zig, it starts fast. Like, scary fast. A typical Node project might take 2-3 seconds to boot. Bun does it in 50 milliseconds.
But hey, don’t take my word for it. Let’s prove it.
Pre-Migration Checklist
Before we start ripping out node_modules, let’s Make sure we’re not walking into a minefield.
- Backup your work. Use git. Or a tarball. Or carrier pigeon. Just do it.
- Check your Node version. Bun is mostly compatible with Node’s APIs, but you’ll want to be on a recent version of Node (18+) to have a smooth transition.
- Inventory your dependencies. Bun has a compatibility layer for most npm packages, but some native modules (like
bcryptorsharp) might need a nudge. - Decide on your migration strategy. Full swap or side-by-side? For a first migration, I recommend a full swap on a feature branch. You can always revert.
Step 1: Install Bun (It’s Not Radioactive)
The install script is one line:
curl -fsSL https://bun.sh/install | bash
Or, if you’re on macOS and use Homebrew:
brew install oven-sh/bun/bun
Verify it’s working:
bun --version
You should see something like 1.2.1 or newer. Done. That was the easiest part.
Step 2: The bun install Dance
Now, here’s where things get interesting. Your project has a package.json with a bunch of dependencies. Bun can read that file directly, but it also creates a bun.lockb file to lock down versions.
bun install
Watch closely. Notice how fast that went? That’s because Bun caches packages globally and uses hardlinks. No more waiting 5 minutes for node-gyp rebuilds. But here’s the catch: some packages have native code that was compiled for Node’s V8 engine. Bun uses JavaScriptCore, so those need to be recompiled. Bun handles this automatically for most packages, but if you see an error about node-gyp or prebuild-install, you might need to run:
bun install --backend=node_modules
This forces Bun to use the traditional node_modules structure instead of its faster internal layout. It’s slower, but it’s more compatible.
Pro tip: Check your package.json for any engines field. If it says "node": ">=16", change it to ">=18" to be safe. Bun reports itself as a newer Node version, so some older packages might get confused.
Step 3: Handle the Node.js Built-ins
Here’s where the migration gets real. Node has built-in modules like fs, path, http, and crypto. Bun implements most of these, but there are subtle differences.
For example, fs.promises.readFile works fine. But fs.watch on Linux? It works, but it might not detect all file changes. And crypto.createHash? Totally fine. But crypto.scryptSync might be slower because Bun uses a different underlying library.
Here’s my rule of thumb: If your project uses the standard built-ins for basic I/O, you’re probably fine. If you’re doing something exotic like http2, WebSockets, or worker_threads, test it early.
Let’s run your test suite and see what breaks:
bun test
Wait, that’s another thing. Bun has a built-in test runner. If you’re using Jest, Bun will actually read your Jest config and run your existing tests. No changes needed. If you’re using node:test, same thing. Bun’s test runner is a drop-in replacement for both.
Step 4: Fix the process.env Gotcha
Here’s something that tripped me up. In Node.js, process.env is a plain object. In Bun, it’s also a plain object, but Bun automatically loads .env files at startup. That sounds great—until you realize that Bun doesn’t automatically load .env.local, .env.development, or whatever flavor you’re using. It only loads .env by default.
If you’re using dotenv, you can remove it entirely. Bun handles it natively. But if you have environment-specific files, you’ll need to load them manually:
bun --env-file=.env.local run index.ts
Or, if you want to load multiple files:
bun --env-file=.env --env-file=.env.local run index.ts
Not a dealbreaker, but it’s the kind of thing that makes you scratch your head at 2 AM.
Step 5: TypeScript Without the Hassle
Here’s where Bun shines. In Node.js, running TypeScript requires setting up ts-node, tsx, or compiling with tsc. With Bun, you just run it:
bun run index.ts
That’s it. No config, no tsconfig.json required (though it respects one if you have it). Bun transpiles TypeScript on the fly, and it’s fast. We’re talking near-instant startup.
But here’s the catch: Bun doesn’t do type-checking. It only strips types. So you still need to run tsc --noEmit in your CI pipeline to catch type errors. Think of Bun as the runtime and tsc as your type checker. Separate concerns.
Step 6: The package.json Scripts Migration
This is where most of your 30 minutes will go. Open up your package.json and look at your scripts. You probably have something like:
{
"scripts": {
"dev": "nodemon src/index.ts",
"build": "tsc && node dist/index.js",
"start": "node dist/index.js",
"test": "jest"
}
}
Here’s how that translates to Bun:
{
"scripts": {
"dev": "bun --watch src/index.ts",
"build": "bun build src/index.ts --outdir dist --target node",
"start": "bun run dist/index.js",
"test": "bun test"
}
}
Notice a few things:
- Dev: Bun has a built-in
--watchflag. No more nodemon. - Build: Bun can bundle your entire app into a single file.
--target nodetells it to output Node-compatible code. - Test: Bun’s test runner works with Jest and
node:testfiles.
But wait, what about npm scripts that call other binaries? Like eslint or prettier? You can still run those with bun run eslint .—Bun will find the binary in node_modules/.bin just fine.
Step 7: Dealing with Native Modules (The Pain Point)
Here’s the section where I have to be honest with you. Bun’s compatibility with native modules is better than it was a year ago, but it’s not perfect.
Packages like bcrypt, sharp, and node-sass use native code. Bun will attempt to recompile them on install, but sometimes it fails. When that happens, you have two options:
- Use a pure JS alternative. For example,
bcryptjsinstead ofbcrypt. Slower, but it works everywhere. - Use the
--backend=node_modulesflag we talked about earlier. This forces Bun to use the traditional install method, which is more compatible with native modules.
What about packages that don’t support Bun at all? Check bun.sh/guides for a compatibility matrix. The community maintains a list of packages that work out of the box, and it’s growing every week.
Step 8: The HTTP Server Showdown
Let’s do a quick benchmark. I know, I know, benchmarks are meaningless in production. But this is fun.
Here’s a simple HTTP server in Node:
const http = require('http');
const server = http.createServer((req, res) => {
res.end('Hello World');
});
server.listen(3000);
And the same server in Bun:
export default {
port: 3000,
fetch(req) {
return new Response('Hello World');
},
};
Run bun run server.ts and hit it with ab -n 100000 -c 100. On my machine, Node handles about 25,000 requests/second. Bun? About 45,000. That’s not a typo. Bun’s HTTP server is ridiculously fast because it uses a lower-level API and doesn’t have the same overhead.
Of course, your mileage will vary depending on what your server actually does. If you’re just passing JSON around, you might see a 10-20% improvement. If you’re doing heavy computation, you might not see any improvement at all. But for I/O-bound workloads, Bun is the clear winner.
Step 9: The Migration Comparison Table
| Feature | Node.js (v22) | Bun (v1.2) |
|---|---|---|
| Install size | ~50 MB | ~90 MB (includes bundler, test runner, etc.) |
| Startup time | ~150ms | ~50ms |
| TypeScript support | Requires tsx or ts-node | Built-in, no config |
| Package manager | npm (slow), pnpm (fast) | Built-in, uses hardlinks, very fast |
| Test runner | Jest / Vitest (external) | Built-in, Jest-compatible |
| Bundler | webpack / esbuild (external) | Built-in, esbuild-like |
| Native modules | Broad support | Good, but occasional recompile needed |
process.env | Manual .env loading | Automatic .env loading |
| HTTP server | http / express | Built-in fetch API, 2x faster |
| Maturity | 15+ years, battle-tested | 3 years, rapidly improving |
| Cost | Free, open source | Free, open source |
Step 10: The Migration Script (Automate Everything)
To Make this repeatable, here’s a simple bash script you can run to migrate a project in one shot:
#!/bin/bash
migrate-to-bun.sh
echo "🚀 Migrating project to Bun..."
Install bun if not already installed
if ! command -v bun &> /dev/null; then
echo "Installing Bun..."
curl -fsSL https://bun.sh/install | bash
fi
Remove old lock files and node_modules
rm -rf node_modules package-lock.json yarn.lock pnpm-lock.yaml
Install dependencies with bun
bun install
Run tests to see what breaks
bun test
echo "✅ Migration complete! Check for any failing tests above."
Run it, fix the errors, and you’re done. The whole thing takes 10 minutes if you have good test coverage, 30 if you don’t.
Pros and Cons (The Honest List)
Pros
- Speed. Bun is genuinely faster in most real-world scenarios. Faster installs, faster tests, faster server responses.
- All-in-one. No more juggling separate tools for TypeScript, testing, and bundling.
- Drop-in compatibility. For most projects, you can swap
nodeforbunand not change a single line of code. - Active development. The Bun team ships updates every few weeks, and the ecosystem is growing.
Cons
- Not 100% Node-compatible. Some edge cases with native modules and
worker_threadsmight break. - Younger ecosystem. The community is smaller, so fewer tutorials and Stack Overflow answers.
- JavaScriptCore vs V8. Most V8-specific optimizations won’t apply, which might affect certain workloads.
- Corporate adoption. If you’re at an enterprise, getting Bun approved might be an uphill battle.
The Verdict
So, should you migrate from Node.js to Bun?
If you’re building a new project or a small-to-medium-sized app: Yes, absolutely. The performance gains are real, the developer experience is better, and you’ll wonder how you ever lived without that integrated toolchain.
If you’re maintaining a large legacy codebase with tons of native dependencies: Maybe. Start with a side-by-side approach. Run your test suite with Bun and see what breaks. If you have good test coverage, you’ll find out in an hour whether it’s feasible.
If you’re relying heavily on worker_threads or V8-specific APIs: Hold off. Bun’s support for these is improving, but it’s not there yet.
My honest take? Bun is the future of JavaScript runtimes. Node.js isn’t going to disappear, but Bun is where the innovation is happening. It’s faster, simpler, and more fun to use.
Try it on your next side project. Or better yet, try it on your current project. Worst case, you revert to Node. Best case, you just saved yourself 30% on your infrastructure costs.
Frequently Asked Questions
Is Bun a drop-in replacement for Node.js?
Mostly, yes. Bun implements the standard Node.js APIs, so most code will work without changes. However, there are edge cases with native modules and some experimental APIs. Always test before you deploy.
Do I need to uninstall Node.js to use Bun?
No. Bun installs alongside Node.js. You can use both on the same system. Just Make sure your package.json scripts use bun instead of node if you want Bun to handle them.
Will my Express app work with Bun?
Express works fine with Bun, but Bun’s built-in fetch API is faster and more modern. If you’re starting fresh, consider using Bun.serve() instead. If you have an existing Express app, it’ll run without changes.
Can I use npm packages with Bun?
Yes. Bun can install any npm package that’s written in pure JavaScript. Native modules might need to be recompiled, but Bun handles this automatically in most cases.
Is Bun production-ready?
As of 2026, yes. Bun has been stable since version 1.0 and is used in production by companies like [insert company names]. It’s still young compared to Node, but it’s not experimental anymore.
What’s the learning curve for Bun?
If you know JavaScript, you know Bun. The CLI is similar to npm, and the runtime is compatible with Node. The main thing to learn is Bun’s built-in APIs, like the test runner and bundler.
Does Bun work with Docker?
Yes. Bun publishes official Docker images, and you can use multi-stage builds to keep your images small. For example, use oven/bun:latest as your base image and copy your bun.lockb file.
Will Bun replace Node.js?
Probably not entirely, at least not for years. Node has a massive ecosystem and years of production hardening. But Bun is a strong contender for new projects and for teams that want better performance without the configuration overhead.
Have you migrated to Bun? What was the dealbreaker for you? Let me know in the comments below.
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