What is Bun? The Node.js Alternative Explained

JavaScript tooling in 2025 feels kind of broken. Starting a new project usually means pulling in five different tools, waiting 30 seconds for a hot reload, and watching your laptop heat up like it’s mining crypto. Everything feels bloated, fragmented, and honestly, slow.

The way we build apps has changed. Microservices, serverless functions, edge deployments. These are all standard now. Performance and developer experience matter more than ever. But instead of getting easier, things feel more complicated.

This is where Bun comes in. It’s a new JavaScript runtime, built from scratch in Zig. It includes a package manager, bundler, test runner, and transpiler. All of it packed into a single binary.

So is Bun the future of JavaScript tooling, or just another fast tool with a short hype cycle? Let’s find out.

What is Bun?

Bun is a modern JavaScript runtime that tries to replace a whole stack of tools with one fast, native binary. It’s not just an alternative to Node. It comes with a built-in bundler, transpiler, test runner, and package manager. No extra installs, no config hell, no Frankenstein toolchains.

You can think of it as if Node, npm, Webpack, Babel, and Jest were merged into one tool and then optimized for speed. That’s the goal.

Bun is written from scratch in Zig, a low-level language focused on performance and safety. Instead of using V8 (the engine behind Node and Deno), Bun runs on JavaScriptCore, the engine used in Safari. This choice helps it stay fast and efficient, both in terms of memory and startup time.

The key idea behind Bun is integration. Everything is built to work together out of the box. No need to glue tools together with scripts and configs. If you’ve ever spent an afternoon trying to fix a broken Webpack build, Bun might feel like a breath of fresh air.

In short, Bun is fast, lightweight, and designed to make modern JavaScript development simpler.

Key Features

So what makes Bun different from everything else? It’s not just about raw speed. It’s about how much it simplifies your workflow while being fast.

Fast Startup and Execution

Bun is built for speed, and it shows in benchmarks. Apps start in around 13ms, HTTP servers handle over 100,000 requests per second, and memory usage stays low. In most benchmark tests, Bun is consistently 2 to 4 times faster than Node.js.

This kind of performance translates to faster reloads, shorter build times, and fewer slowdowns in your development flow.

All-in-One Toolchain

Bun replaces a whole stack of tools with one binary:

• Bundler – Native and fast. Supports code splitting, tree shaking, and modern JS out of the box.
• Transpiler – Full support for TypeScript and JSX. No need for Babel or tsc.
• Package Manager – Installs packages up to 30x faster than npm, thanks to hardlinking.
• Test Runner – Built-in, zero-config, and noticeably faster than Jest or Vitest.
• More Built-ins – Includes a native HTTP server, .env loader, SQLite support, and more.

No extra installs. No fragile plugin setups. Everything just works together.

Single Binary, Zero Config

You install Bun with one command. That’s it. No need to wire up a bunch of tools or write pages of config files. Just run bun dev and start coding.

Ecosystem & Compatibility

One of the best things about Bun is how much of your existing JavaScript setup it supports. You don’t have to change everything to start using it.

Node.js and npm Compatibility

Bun supports most of the Node.js API: things like fs, path, http, and more. A lot of popular libraries just work, including web frameworks like express. It’s not full coverage yet, but for many apps, it’s close enough that you can switch without major rewrites.

Bun also works with the npm registry out of the box. You can install most packages the same way you’re used to. Instead of relying on npm’s slower install process, bun install is built from scratch with speed in mind. It resolves dependencies, parses lockfiles, and links packages way faster than npm or Yarn, usually done before you expect it.

ESM and CommonJS Support

Bun supports both modern ESM import and older CommonJS require() in the same project. No extra config, no hacks. You just write code and it works.

What Doesn’t Work (Yet)

Some things are still in progress. Bun doesn’t support every Node.js API, especially lower-level modules or native add-ons. If your project uses edge-case features or complex build tooling, expect a few rough edges.

But the project moves quickly, and bugs tend to get addressed fast. If something doesn’t work, check GitHub, or open an issue.

Quickstart Example

Let’s see how Bun works in practice.

Step 1: Install Bun

The easiest way to install Bun is through npm (if you already have Node.js):

npm install -g bun

Alternatively, you can use a package manager like Homebrew on macOS or PowerShell on Windows. Full instructions are available at bun.sh.

To confirm it’s working:

bun --version

You should see something like bun 1.x.x.

Step 2: Initialise a Project

Start a new project with:

bun init

It will ask you a few questions and generate a basic setup with an index.ts or index.js file.

Step 3: Run Your Code

Here’s a simple HTTP server example, taken straight from the Bun docs. Drop this into a file called index.ts:

const server = Bun.serve({
  port: 3000,
  fetch(req) {
    return new Response("Bun!");
  },
});

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

Then run it:

bun run index.ts

That’s it. You’ve got a working server and dev setup in under a minute.

Conclusion

Bun is a fresh, fast take on JavaScript tooling with a single binary that does it all, from running code to managing packages and tests. The focus on speed and simplicity really shows.

It’s still early days. Some features are missing and there are rough edges. But development is moving fast and the core experience already feels solid.

Plus, the logo is literally a happy bread roll. What’s not to love?

In the next article, we’ll build a simple project with Bun and see how it performs beyond just “hello world.”