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Manuel Aparicio
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What is Bun JavaScript Runtime?


There’s been a great buzz around a new Software Development tool that promises to be a major milestone in the JavaScript ecosystem. As you may know, developing top-notch software products goes beyond Front- and Back-End frameworks and Database Management Systems (DBMS). There are many tools developers have to use to ensure everything works properly! In this context, JavaScript is currently the most popular programming language globally because of its maturity, versatility, and efficiency. Yet, things can get messy with all the tools required to develop JavaScript applications.

That's why a new utility belt eliminated the need for additional tools to handle some of the most annoying aspects of JavaScript development! Bun is an all-encompassing JavaScript toolkit that aims to support advanced Web Development practices in the Developer Experience of concurrent users. One of the main reasons it’s become so popular is for being a much more efficient and secure runtime than the well-established Node.js. However, there’s much more to it than just being a lightweight runtime environment.

What is Bun in JavaScript?

Bun is a fast, all-in-one JavaScript runtime with a massive toolkit Node.js-compatible package manager that handles built-in testing support, improving developer productivity. Plus, it comes with a robust bundler, giving developers a world-class experience when building complex apps with JavaScript. Bun is a big new thing for the JavaScript engine, which uses a powerful and low-level programming language called Zig. For starters, Zig can outperform Rust and even C, the OG programming language, in a wide range of common tasks, which explains why Bun is remarkably fast. It’s clear why they call it an all-in-one tool! Yet, while one might think that, since it has the power of an all-in-one tool, it wouldn’t rival the other tools’ performance, that can’t be further from the truth!

Bun’s largely outperforms most JavaScript runtimes, bundlers, and package managers. In fact, Bun has faster start times than Node.js and Deno when working with TypeScript and 26x times faster than pnpm! To give you a deeper perspective, it takes over 10 seconds to compile your code with an npm package, but with Bun, it takes less than half a second. Bun is powerful and has faster startup times because it uses JavaScriptCore, which tends to outperform other options like the JavaScript V8 engine.

How Does Bun Work?

As mentioned, Bun uses the JavaScriptCore engine to achieve its insane performance levels. Yet, you have to know more to understand how efficient it is. With a strong focus on performance, Bun uses tagged pointers to avoid the overhead of storing function pointers separately. Bun’s team built it from the ground up with the help of many investors and collaborators. Having the luxury of building a project from scratch helped optimize, step by step, every little aspect to guarantee Bun offers great performance levels. Also, they leveraged Zig's power, allowing for manual memory usage management. Another standout feature is that Bun APIs (Application Programming Interfaces) use web-standard APIs like WebSocket, fetch, and ReadableStream to handle HTTP requests and environment variables without downloading additional package installations. 

In terms of getting started, things are much easier with Bun since you no longer need tons of configuration files. That, combined with its seamless built-in TypeScript support, allows you to start writing TypeScript code in the blink of an eye. Its transpiler processes TypeScript (ts) files without any configuration. On top of that, it also has strong support for React.js and hot reloading out-of-the-box. Since it works as a package manager, it can replace any npm run command with “bun run” to run scripts. Needless to say, Bun's modern key features focus on speed. It’s worth noting that Bun aims for compatibility with Node modules. Hence, you don’t need to start from scratch, reinventing the wheel.

Bun JavaScript vs Node.js

Bun’s team has presented Bun as an all-in-one drop-in replacement for built-in Node.js modules, showing that it is significantly faster. The fact that Bun is compatible with Node.js makes it a viable option for the development process of new and existing projects. Yet, there are quite a few more things to take into consideration. Node.js is a much more mature tool with a larger standard library and a vast community of developers and collaborators. Its team has been working on improving performance recently to keep up with new tools. While Bun seems faster and more convenient because of its high-performance tooling (thanks to its server-side JavaScript runtime), we must consider that, unlike Node.js, Bun’s creators used large amounts of money to build it. As a result, Bun’s team may probably try to monetize it.

Why Use Bun?

One of the main reasons Bun has become a compelling alternative is its high performance levels. However, it wouldn’t be fair to say Bun is all about blistering speed and performance. What makes Bun so special is how it eliminated most of the complexities of working with JavaScript but keeping the cool stuff. Complexities include tons of configuration files and separate tools you must use to build a JavaScript program. It solved the annoying problem of transitioning from CommonJS to ES Modules. With Bun, you can import and require in the same file extension. No more weird specifications.

The JavaScript cool stuff I mentioned includes React.js and TypeScript support and compatibility with Node.js and npm commands. Besides, Bun uses its transpiler for .js, .ts, .cjs, .mjs, and .tsx files and native Application Programming Interfaces (APIs). That also helps explain why it’s so efficient. Let’s not forget that the Bun test runner and debugger are compatible with the Jest testing framework. One more thing worth noting is that Bun works perfectly with Elysia.js, which claims to be nearly 20 times faster than Express and Node.js.


As a full-cycle digital agency focusing strongly on the advanced world's server-side JavaScript projects, we’re very excited about how Bun's modern features will shape the future with its optimal performance. Although we can only endorse Node.js capabilities with stacks like MERN, we can’t ignore that Bun's built-in modules make it a promising and robust tool. It seems clear that it'll help streamline the Product Development Lifecycle of complex applications in the JavaScript and TypeScript runtime landscape. It will also help deliver products with a seamless User Experience (UX) by offering an improved Developer Experience.