Bun is an all-in-one toolkit for running, building, testing and debugging JavaScript and TypeScript applications. It focuses on performance and developer experience, aiming to unify the fragmented JavaScript tooling ecosystem.

What exactly is Bun?

At its core, Bun is a JavaScript runtime, similar to Node and Deno. Which allows JavaScript to interact with lower-level system resources like the file system and network services. Before JavaScript runtimes like these existed, JavaScript was confined to running only in web browsers. It was simply a programming language for the web.

Bun focuses on developer experience and performance.

The state of tooling in the JavaScript ecosystem is somewhat fragmented. A lot of tools are required when your starting a project for transpiling, bundling, testing, etc. Bun attempts to improve the developer experience by reducing the number of additional tools you need.

Running JavaScript or TypeScript

bun index.ts

Bundling code

bun build ./index.tsx --outdir ./out

Running tests

bun test

Package manager and runner

bun install
bunx my-cli

Comparing Bun and Node runtimes

Bun uses JavaScriptCore, the JavaScript engine used in Safari. This engine offers quicker startup time compared to V8 used by Node.

Previously, JavaScriptCore was also used in React-Native due to its faster startup times. Ever since React-Native has transitioned to an engine named Hermes, which is specifically designed for the React-Native use-case.

The API layer of Bun is written in ZIG, a low-level programming language, whereas the API layer of Node is mainly written in C++. ZIG, which was released in 2016, didn’t exist when Node was created. Often referred as the next generation alternative to the C programming language, ZIG is recognized for its speed and simplified memory management.

I believe that the performance improvements in Bun are due to its use of JavaScriptCore and a performance-focused API layer. Utilizing JavaScriptCore can lead to faster startup times when installing packages, running tests, and executing code. Unlike Node, Bun’s API layer is fundamentally designed for performance. Unlike Node, it does not have a codebase that’s over a decade old.

Node is a mature project, over a decade old, and currently in version 20. In contrast, Bun is a newcomer that does not maintain a similarly aged codebase. Node, being battle-tested and relied upon by a considerable amount of global code, cannot afford to be as experimental with its runtime. On the other hand, Bun, being in its early stages, has the freedom to be more experimental.

List of built-in features

• Supports TypeScript and JSX natively
• Includes a built-in SQLite database
• Provides built-in support for environment variables
• Features built-in support for Web Sockets

Node compatibility

Bun is compatible with the Node API, enabling easy replacement of Node with Bun in your project. This gives you access to all the packages available on NPM.

CommonJS and ES module support

One of the most exciting features of Bun is the ability to use both CommonJS and ES modules in the same file, relieving developers from having to choose between the two.

import lodash from "lodash";
const _ = require("underscore");

Final Thoughts

Bun introduces many innovative features to the JavaScript ecosystem and pushes Node to improve. While I believe that Node isn’t going anywhere, it’s exciting to see how Bun’s fresh ideas might influence Node’s future development.

Ultimately, Bun aims to improve the developer experience by reducing the number of tools required in a project. It’s a promising addition to the JavaScript ecosystem that’s worth keeping an eye on.