Getting Started with Bun.js: A Quick Guide

JavaScript frameworks and runtimes are constantly evolving, and Bun.js is here to shake things up.

It’s not just another tool for developers – it’s a performance-focused JavaScript runtime that promises faster execution and a simpler, more efficient development experience.

Let’s explore what Bun.js offers, how it works, and why it might just be the next big thing in JavaScript development.

What is Bun.js?

Bun.js is a modern JavaScript runtime built from scratch with performance as its top priority. It’s designed to work effortlessly with JavaScript, TypeScript, and JSX, making it a versatile tool for developers across the board.

Bun is aiming to outpace Node.js and Deno, using cutting-edge technology to run JavaScript at lightning speed while also enhancing the development experience.

What sets Bun apart is that it’s built with Rust, which offers low-level system access for optimizations that other runtimes can’t achieve.

This unique architecture means faster startup times, less memory usage, and quicker execution, making Bun an exciting option for developers looking to boost their workflow.

Why Choose Bun.js?

1. Unmatched Performance

Bun.js is all about speed. It’s one of the fastest JavaScript runtimes out there, executing code at lightning speed.

Building APIs, running server-side JavaScript, or handling complex tasks? Bun gives you a serious performance boost. Plus, it comes with a fast bundler that compiles your code quickly, so you spend less time waiting and more time coding.

2. Built-in Tooling

Bun comes with everything you need – no third-party tools required. It includes a bundler, transpiler, and package manager all built-in. No more extra setup – just install Bun, and you’re good to go. Here’s what’s included:

• Bun bundler: Fast bundling for JavaScript, JSX, and TypeScript.
• Bun transpiler: Converts TypeScript and JSX into JavaScript.
• Bun package manager: Faster and more efficient than npm or Yarn.

3. Simplified Development Workflow

Bun makes development smoother with fast startup times, quick hot reloading, and minimal configuration. If slow build times and reloading have been a pain, Bun is a game-changer that helps you get your projects running faster.

4. Compatibility with Existing Ecosystems

Worried about compatibility? Bun works easily with popular libraries and frameworks like React, Vue, and Express, so you won’t run into compatibility issues when you switch.

How Bun.js Works

Bun.js takes advantage of the V8 engine, like Node.js and Deno, but optimizes execution in several key ways.

Using Rust for low-level system calls, Bun achieves near-native performance. Its bundler leverages ES modules to simplify the build process and boost efficiency.

Bun also supports the vast majority of JavaScript and TypeScript features, including ES modules and async/await. This means you can harness the full power of JavaScript without compromising performance.

Built-in TypeScript Support

Bun makes working with TypeScript effortless. No need for complex configurations or extra setup—just write your TypeScript code, and Bun takes care of the rest.

Here’s the magic: Bun automatically detects TypeScript files and compiles them behind the scenes. It natively supports .ts and .tsx files, so whether you're building a React app or a Node.js server, TypeScript works right out of the box.

But it doesn’t stop there. Bun also offers built-in type checking, helping you catch pesky type errors early without needing an extra tool. And with its fast performance, slow compilation times are a thing of the past.

With Bun, you get a smooth TypeScript experience that just works—no headaches, no extra steps.

Bun vs. Other Runtimes

When considering Bun.js, it’s helpful to compare it with other popular JavaScript runtimes like Node.js and Deno.

Bun vs. Node.js

Node.js has been the go-to runtime for years, but it’s not exactly known for speed. Bun was built to address this shortcoming, easily outpacing Node.js in execution speed. On top of that, Bun comes with integrated tooling, giving it a significant edge over Node, which requires extra configuration and third-party tools.

Bun vs. Deno

Deno, designed as a modern alternative to Node.js, focuses on security and TypeScript support. While it offers some great features, Bun still takes the lead in terms of performance.

With its speed, native bundler, and package manager, Bun provides a more complete and performant development environment, making it a strong contender in this space.

Bun Tooling Features

Bun is packed with powerful tools that make your development workflow fast, efficient, and easy to use. It's designed to help you build applications without the hassle, offering a suite of features that make life a whole lot easier.

1. Bundling

Bun’s bundler is super fast. It compiles and bundles your code quickly, meaning you spend less time waiting around and more time building. With minimal setup, you can bundle TypeScript, JavaScript, and even JSX/TSX files, making it perfect for modern web apps.

2. Transpiling

Bun handles transpiling out of the box, turning modern JavaScript features into something that works in older environments. It automatically processes TypeScript, JSX, and more, so you don’t need separate tools like Babel. Everything you need is already built in.

3. Fast HTTP Server

Bun includes a lightweight, super-fast HTTP server. Whether you're running a simple API or a full-blown application, this server can handle it without breaking a sweat. It processes requests efficiently, ensuring smooth performance.

4. Task Runner

Bun comes with a built-in task runner to automate your workflows. Whether it’s running tests, building assets, or deploying your app, you can automate everything with minimal setup. This gives you a smoother, more consistent workflow without relying on third-party tools.

5. Native ES Modules Support

With Bun, ES modules are fully supported, so you can work with modern JavaScript features like import and export easily. No need to worry about compatibility issues—just write clean, modular code.

6. Built-in Package Manager

Bun has its own package manager, making dependency management a breeze. It’s optimized for speed, so you’ll notice much faster installs compared to traditional package managers like npm or Yarn.

Bun Configuration Options

Bun offers several configuration options that let you fine-tune its behavior to suit your needs. These settings give you control over everything from bundling and transpiling to server settings. Let’s explore some of the key configuration options in Bun.

1. bunfig.toml

The heart of Bun’s configuration is the bunfig.toml file. This is where you define your project’s build settings, dependencies, and preferences. It helps you customize how Bun behaves across your entire project.

2. Bundling Settings

You can customize how Bun bundles your code with options like:

• Entry points: Set where the build process starts.
• Output directory: Choose where your final bundled files will be saved.
• Minification: Enable or disable code minification to reduce bundle size.
• Target environment: Pick whether you’re bundling for the browser, Node.js, or other environments.

3. TypeScript Configuration

Even though Bun has built-in TypeScript support, you can tweak settings to fit your needs:

• Type checking: Enable or disable type checking during the build.
• Paths mapping: Customize how Bun resolves module paths, especially for custom directories.
• Strict mode: Turn on TypeScript’s strict mode for more precise type checks.

4. ESModules & Transpiling

Bun gives you flexibility in handling ESModules and modern JavaScript features:

• Enable/disable ESModules: Toggle between working with CommonJS modules or disabling ESModule support.
• Transpile to specific versions: Set a target for transpiling, like a specific JavaScript version or a particular browser.

5. Server Configuration

You can adjust settings for Bun’s built-in HTTP server, including:

• Port: Set the port number for the server to listen to.
• Middleware: Add custom middleware to handle requests before they hit your routes.
• Base path: Customize the base path if your app is served under a subdirectory.

6. Plugins

Bun supports plugins to extend its functionality. You can either add custom plugins or adjust existing ones to modify how Bun handles different file types, manages assets, or integrates with external tools.

7. Package Manager Options

For those using Bun’s package manager, there are a few tweakable settings related to dependency management:

• Install flags: Customize installation flags, like choosing a specific registry or forcing a clean install.
• Cache settings: Control how Bun handles caching dependencies to speed up future installs.

These configuration options give you the power to shape Bun’s behavior to perfectly fit your project.

Installation Methods in Bun

1. Using the Official Script (Recommended)

The fastest way to install Bun is by running the official installation script. It works across macOS, Linux, and Windows (via WSL). Just enter the following in your terminal:

curl -fsSL https://bun.sh/install | bash

This command will download and install Bun, and automatically add it to your system's PATH for easy access.

2. Homebrew (macOS / Linux)

For macOS or Linux users who prefer Homebrew, installing Bun is effortless:

brew install bun

Homebrew will handle the installation and keep Bun up-to-date for you.

3. Windows Subsystem for Linux (WSL)

If you're on Windows, you can install Bun via WSL (Windows Subsystem for Linux). Here's how:

1. Install WSL and a Linux distribution like Ubuntu.
2. After setting up WSL, run the official script in your WSL terminal:

curl -fsSL https://bun.sh/install | bash

Bun will be installed in your WSL environment, making it available for use on Windows.

4. Binary Releases (All Platforms)

For a manual installation, you can download the latest Bun binary directly from the official GitHub Releases page. Choose the correct version for your operating system and architecture, then follow the instructions for installation.

5. Docker

If you prefer working in containers, you can use Bun in a Docker container. Here's how:

docker run --rm -v $(pwd):/app -w /app bun/bun <command>

This is a great option for CI/CD pipelines or isolated development environments.

6. NPM (Experimental)

For those who want to try Bun without installing it globally, you can use npm, though this method is still experimental:

npm install -g bun

7. Manual Installation (Advanced)

If you want to fully customize your installation, you can manually download the source code and follow the build instructions on Bun’s official GitHub repository. This method is for advanced users who want complete control over the installation.

Once installed, confirm everything is working by checking the version with:

bun --version

How Bun Simplifies Dependency Management

Bun comes with its own package manager that’s fast, efficient, and super easy to use. It makes installing, updating, and managing your dependencies a breeze.

Here’s how it works:

1. Installation Speed

Bun’s package manager is designed to be lightning-fast. Whether you’re installing one package or all the dependencies for a project, Bun speeds up the process. It’s way quicker than npm or yarn, thanks to some smart optimizations under the hood.

2. Single Command Install

No need for long commands. Just run:

bun install

And done! All the dependencies from your package.json or bunfig.toml file are installed in no time.

3. Dependency Resolution

Bun takes care of resolving and installing the right versions of your packages, so you don’t have to stress about version conflicts. It handles that in the background, making your life easier.

4. Package Locking

Bun uses a lock file (bun.lockb) to make sure your dependencies stay consistent across different environments. This means you won’t run into any issues with mismatched versions, especially when working in a team.

5. Updating Dependencies

Keeping things up to date is super simple:

• To update a specific package, just run:

bun upgrade <package-name>

• To update everything:

bun upgrade

You’re always working with the latest version—no hassle.

6. Local and Global Dependencies

Bun supports both local (specific to your project) and global (available across your system) dependencies. To install a global package, just run:

bun add -g <package-name>

7. Built-in Cache

Bun speeds things up even more by caching installed packages. So, once a package is installed, it’s stored locally, and future installs won’t require downloading it again.

8. Dependency Audits

While Bun doesn’t have a built-in audit command, you can still integrate external tools for checking vulnerabilities in your dependencies.

In short, Bun makes dependency management smooth, fast, and hassle-free.

Standard Library and Web APIs

Bun comes with a comprehensive standard library and supports a variety of Web APIs to simplify your development process.

Handling file operations, networking, or real-time data, Bun’s focus on performance and ease of use makes working with modern JavaScript features and web technologies a breeze. Let’s break down some of the key features:

1. File System API

Bun’s File System (FS) API allows you to read from and write to files, work with directories, and perform other file operations. It’s designed for speed, offering both synchronous and asynchronous operations depending on your needs.

2. Networking and HTTP

Bun simplifies networking with an HTTP server and client APIs. The built-in HTTP server is optimized for speed, and it supports both fetch and XMLHttpRequest for making network requests. It’s fully compatible with modern web standards, whether you’re working on the client-side or server-side.

• WebSockets: Bun also supports WebSockets for real-time communication between clients and servers.

3. Timers and Event Loop

Bun offers efficient timer utilities like setTimeout and setInterval, which helps handle asynchronous tasks with minimal overhead. It integrates smoothly with the event loop, ensuring tasks run efficiently.

4. URL and Query String

With Bun, working with URLs and query strings is simple. The URL and URLSearchParams APIs make it easy to parse, manipulate, and construct URLs, which is especially useful for building dynamic web applications.

5. Web Streams API

Bun supports the Web Streams API, enabling you to handle streaming data effectively. Whether you're working with large datasets or real-time data, this API lets you read, write, and transform streams without loading everything into memory at once.

6. Web Storage API

For client-side storage, Bun supports the Web Storage API, including localStorage and sessionStorage. This allows you to persist data across sessions or manage session-specific information.

7. Web Crypto API

The Web Crypto API in Bun lets you perform cryptographic operations, such as hashing, encryption, and decryption. It’s essential for building secure applications that handle sensitive data.

8. Text Encoding and Decoding

Bun supports the Text Encoding and Decoding API, which is useful for working with different character encodings. This is especially helpful when dealing with internationalization or binary data.

9. Streaming API

Bun’s streaming capabilities allow you to process data in chunks without loading everything into memory. It’s perfect for applications that need to handle large amounts of data efficiently.

10. Import Maps

Bun supports import maps, a web API for controlling module resolution. This lets you map module specifiers to specific URLs, helping to optimize module loading and manage different versions of dependencies.

11. Environment Variables

Bun makes it easy to manage environment variables, which you can access in a way that’s compatible with Node.js-style apps. This is useful for configuring your app’s behavior across different environments like development, staging, and production.

12. Service Workers

Bun supports Service Workers, enabling you to create powerful offline experiences and background sync capabilities. You can intercept network requests, cache assets, and handle push notifications, making it easier to build modern web applications that work offline or in unreliable network conditions.

Use Cases for Bun.js

1. Fast APIs

Bun’s speed makes it perfect for building APIs that need to handle a large number of requests quickly. Whether you’re creating a microservice or a full-scale API, Bun ensures your application can scale smoothly without hitting performance bottlenecks.

2. Server-Side Rendering (SSR)

For front-end frameworks like React or Vue, Bun makes server-side rendering a breeze. With its fast bundler and optimized performance, your SSR pages will load quickly, enhancing the user experience for your audience.

3. Full-Stack Applications

Bun offers full-stack developers a simplified environment for both front-end and back-end code. With its built-in tools and lightning-fast performance, you can focus on building features instead of managing dependencies.

Conclusion

Bun.js is not just a fast JavaScript runtime; it’s a complete development ecosystem built with performance and simplicity at its core.

With native bundling, transpiling, and package management tools, Bun's your development process. Its speed ensures that JavaScript code executes more efficiently, making it an excellent choice for modern projects.

FAQs

What is Bun.js?

Bun.js is a modern JavaScript runtime designed for speed, offering an alternative to Node.js and Deno. It's built to provide faster startup times and better performance, especially with its optimized JavaScriptCore engine and the use of Zig for low-level improvements.

How does Bun.js compare to Node.js and Deno?

Bun.js is faster than both Node.js and Deno due to its high-performance JavaScriptCore engine and use of Zig for low-level optimizations, ensuring quicker execution and better overall performance.

Can Bun.js run benchmarks?

Yes, Bun.js includes built-in tools to run benchmarks and test performance, making it easy to measure and improve speed in your projects.

How does Bun.js work with Next.js?

Bun.js can replace Node.js in Next.js projects, offering faster startup times and improved performance for server-side operations, making it a great choice for Next.js users.

Can I use Bun.js with Vite?

Yes, Bun.js works well with Vite, helping manage development environments with fast hot module reloading for efficient modern JavaScript development.

What is bun.serve?

bun.serve is a feature that enables you to quickly start a server, similar to using Express in Node.js, but with enhanced performance for serving HTML, CSS, and JavaScript files.

Is Bun.js open source?

Yes, Bun.js is open source, allowing you to contribute or use it freely in your projects. You can find the repository on GitHub for more details.