The JavaScript ecosystem has grown immensely over the past decade, with Node.js serving as the backbone for server-side JavaScript since 2009. But lately, there’s been a lot of buzz around Bun, a new JavaScript runtime that promises to be faster, lighter, and more efficient. Created by Jarred Sumner, Bun aims to provide a fresh alternative to Node.js, with a specific focus on speed and developer experience.

In this review, I’ll dive into Bun—what it brings to the table, how it compares to the existing options like Node.js and Deno, and my own experiences working with it. From its lightning-fast performance to its streamlined developer tooling, Bun is generating a lot of excitement, and it’s easy to see why.

What is Bun?

Bun is a JavaScript runtime designed to run on JavaScriptCore, the same engine that powers Safari. Like Node.js and Deno, Bun lets developers write server-side applications using JavaScript (and TypeScript). However, Bun sets itself apart with its intense focus on speed, native bundling, and ease of use.

Bun claims to be faster than both Node.js and Deno, offering a more efficient way to build and execute JavaScript applications. But Bun is more than just a fast runtime—it’s also a bundler, package manager, and task runner, all rolled into one.

Here’s a quick breakdown of the core features of Bun:

1. Speed: Bun is optimized for performance, claiming to be 3x faster than Node.js in certain benchmarks.

2. Native bundling: Unlike Node.js, Bun has a built-in bundler that compiles JavaScript, TypeScript, JSX, and other web formats with lightning speed.

3. Package management: Bun can manage npm packages directly, offering an alternative to npm and yarn.

4. Batteries-included philosophy: Bun includes many features out-of-the-box, such as Web API implementations and TypeScript support, making it a highly productive environment for modern JavaScript developers.

With this combination of features, Bun aims to streamline the development process, reduce dependencies, and supercharge performance.

Why Bun? The Performance Factor

The first thing anyone hears about Bun is its speed. Bun's creators promise significant performance improvements over both Node.js and Deno, particularly in key areas like:

1. Startup time: Bun’s cold-start speed is incredibly fast, reportedly booting applications up to 3x faster than Node.js.

2. Package installations: Installing npm packages with Bun is blazingly fast compared to npm and yarn.

3. Bundling and compiling: Bun comes with a built-in bundler that compiles JavaScript, TypeScript, and JSX in a fraction of the time it takes with other bundlers like Webpack or Parcel.

In my own experience, I’ve found the speed claims to be accurate, especially in terms of startup time. I ran a few quick tests with both small and large applications, and Bun consistently outperformed Node.js in booting servers and loading modules. Here’s a simple comparison I ran:

Compared to Node.js, Bun’s startup time was noticeably faster. While Node.js is still robust, you can't ignore the difference Bun makes if you're dealing with high-traffic, performance-sensitive applications.

Built-in Bundler: Say Goodbye to Webpack?

One of the features that got me really excited was Bun’s native bundler. If you’ve worked with Webpack, Parcel, or Rollup, you know how critical (and sometimes painful) the process of bundling can be, especially in large-scale applications. Bun takes this process and integrates it into the runtime itself, which simplifies both setup and execution.

Bun’s bundler natively supports:

- JavaScript

- TypeScript

- JSX/TSX

And it’s all done out-of-the-box, meaning you can write your code and let Bun handle the bundling without needing a separate tool like Webpack or Rollup. In my own experience, this integration saved a lot of time and configuration hassle. I didn’t need to wrestle with config files or worry about which bundler plugin to install—Bun just handled it.

For instance, bundling a simple React project with Bun felt almost magical. Here’s a basic JSX example:

Using Bun’s bundler, it was straightforward to turn this JSX file into a minified, production-ready JavaScript bundle with almost no setup. It’s an incredibly useful feature, especially for front-end developers who are tired of managing separate bundling tools.

Built-in Package Manager: npm Alternative?

Bun also introduces a built-in package manager that can replace npm and yarn. Unlike Deno, which shunned npm entirely (though it later introduced partial support), Bun is fully compatible with npm packages. This means you can still use your favorite npm libraries, but without the slow install times often associated with npm or yarn.

Here’s where Bun truly shines. Installing a package with Bun’s package manager is lightning-fast. For example, installing express in Node.js usually takes a bit of time due to npm's relatively slower handling of package resolutions. With Bun, the same operation is nearly instantaneous:

Bun’s package manager feels more streamlined, and it doesn't get bogged down by bloated node_modules folders, which we’re all too familiar with in the Node.js world. However, it's still early days for Bun’s package manager, and I encountered a couple of small issues with less-common packages. Still, it’s promising and could easily grow into a serious contender for npm.

Web APIs: A Nod to the Browser Environment

One of Bun's more interesting features is its inclusion of built-in Web APIs. Unlike Node.js, which doesn’t align perfectly with browser APIs, Bun includes several modern web APIs that make it more familiar to front-end developers.

For instance, Bun supports Fetch API, WebSocket, ReadableStream, and more, allowing developers to write code that is almost identical to what they’d write for a browser environment. This feature makes it much easier to write universal code that can run both server-side and client-side, which is a major plus if you’re building full-stack applications.

Here’s an example of using the Fetch API in Bun, which looks exactly like what you’d do in the browser:

As a front-end developer, this makes the transition between writing browser code and server code feel more seamless. I found this approach particularly useful in reducing the mental overhead of switching contexts between the server and client.

TypeScript Support

Like Deno, Bun also comes with TypeScript support built-in. You don’t need to install or configure any TypeScript compiler manually. Just write your TypeScript, and Bun takes care of the rest.

This is great news for developers who love the safety and developer experience that TypeScript offers but are tired of the additional configuration overhead that comes with setting it up in Node.js. In Bun, everything is built-in and ready to go. Here’s a quick TypeScript example in Bun:

In my personal projects, Bun’s TypeScript handling felt as smooth as expected, with zero configuration necessary. It was quite refreshing to get TypeScript support “for free” without having to set up tsconfig.json or run tsc.

Ecosystem and Compatibility

One of the main questions surrounding any new JavaScript runtime is compatibility with existing ecosystems, particularly npm. While Bun provides first-class support for npm modules, it doesn’t yet have the ecosystem maturity that Node.js enjoys.

For example, if you rely heavily on specific Node.js features, such as native modules or older APIs, you might run into issues when trying to use them in Bun. The community around Bun is still growing, and while it’s incredibly promising, it’s not as battle-tested as Node.js or even Deno at this stage.

That said, Bun’s compatibility with npm packages gives it a significant advantage over Deno, which has struggled with ecosystem fragmentation due to its reliance on URL-based imports. If you’re looking to use Bun as a replacement for Node.js, you’ll find that most popular npm libraries work seamlessly, but you may hit occasional bumps with more niche or older packages.

My Personal Experience with Bun

I’ve spent a good amount of time experimenting with Bun, and it’s left quite an impression. Here are a few key takeaways from my experience:

1. Speed is real: Bun lives up to the hype in terms of performance. Whether it’s starting a server, bundling files, or installing packages, Bun is significantly faster than anything else I’ve used in the JavaScript ecosystem.

2. The tooling is delightful: Having a runtime, bundler, and package manager all in one tool is a massive time-saver. I was able to set up a full project, from development to production, with fewer steps and less configuration than with Node.js.

3. Learning curve: If you’re coming from a Node.js or front-end background, Bun is relatively easy to pick up. The fact that it aligns closely with modern Web APIs makes the transition seamless, especially for front-end developers like myself.

4. Room for improvement: While I’m excited about Bun, there are still some rough edges, particularly around package compatibility and ecosystem maturity. However, considering that Bun is still young, I expect these issues will be ironed out as the community grows.

Conclusion: Is Bun the Future of JavaScript Runtimes?

Bun is an exciting new entrant in the JavaScript runtime space. Its emphasis on speed, ease of use, and built-in tooling makes it a highly attractive alternative to Node.js and even Deno. For developers who value performance and want a simpler, more streamlined workflow, Bun is absolutely worth trying out.

However, Bun isn’t without its limitations. While the npm compatibility is impressive, there are still some quirks with less common packages, and the ecosystem around Bun is still in its early stages. But the potential here is undeniable. If Bun continues to grow at its current pace, it could become a serious contender for Node.js’ throne in the JavaScript world.

In the end, Bun offers a glimpse into what a modern JavaScript runtime could look like—fast, secure, and developer-friendly. For me, Bun has quickly become a tool I’m excited to watch, and I’ll definitely be using it in future projects. If you haven’t tried it yet, I highly recommend giving Bun a spin.