Getting Started with Bun: The Fast All-in-One JavaScript Runtime

Question

The JavaScript ecosystem has traditionally relied on multiple tools:

• Node.js for runtime
• npm/yarn/pnpm for package management
• Webpack/Vite for bundling
• Jest/Mocha for testing

But modern development demands speed, simplicity, and fewer tools.

This is where Bun comes in.

Bun is an all-in-one JavaScript runtime designed to replace many tools in the modern development stack while being extremely fast.

In this guide, you'll learn:

• What Bun is
• Why developers are switching to it
• How to install and run your first app
• Best practices for using Bun in real projects

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What is Bun?

Bun is a JavaScript runtime + toolkit built for performance.

Unlike traditional setups where you install many tools separately, Bun includes:

• JavaScript runtime
• Package manager
• Bundler
• Test runner
• Task runner

All inside one tool.

Bun is written in Zig and uses the JavaScriptCore engine.

This combination makes it significantly faster than traditional Node workflows in many scenarios.

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Why Developers Are Excited About Bun

Bun focuses on developer experience and performance.

Key advantages:

Extremely Fast Package Installation

Instead of downloading packages repeatedly, Bun caches them efficiently.

Example:

bun install

This often runs 2–10x faster than traditional package managers.

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Built-in Tools

With Bun you don’t need to install:

• separate bundlers
• separate test frameworks
• extra script runners

One command handles most tasks.

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TypeScript Support Out of the Box

Bun runs TypeScript without additional configuration.

Example:

bun run index.ts

No build step required.

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Installing Bun

Install Bun using a single command:

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

After installation, verify:

bun --version

If you see a version number, Bun is ready.

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Creating Your First Bun Project

Create a new project:

bun init

This generates a project structure like:

my-bun-app
 ├─ bun.lockb
 ├─ package.json
 ├─ index.ts
 └─ node_modules

Bun automatically configures the project.

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Running Your First Script

Create index.ts:

console.log("Hello from Bun!");

Run the file:

bun run index.ts

Output:

Hello from Bun!

Bun executes TypeScript without transpiling manually.

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Installing Packages

Bun works with the existing npm ecosystem.

Install a dependency:

bun add axios

Install dev dependency:

bun add -d typescript

Remove a package:

bun remove axios

Bun also creates a fast lockfile:

bun.lockb

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Running Scripts

Scripts inside package.json work the same way.

Example:

{
  "scripts": {
    "dev": "bun run index.ts"
  }
}

Run:

bun run dev

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Building HTTP APIs with Bun

Bun includes a built-in HTTP server.

Example API server:

Bun.serve({
  port: 3000,
  fetch(req) {
    return new Response("Hello from Bun API!");
  },
});

Run:

bun run server.ts

Open:

http://localhost:3000

This creates a high-performance API server with minimal code.

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Running Tests with Bun

Bun includes a built-in test runner.

Create a test:

import { expect, test } from "bun:test";

test("addition works", () => {
  expect(2 + 2).toBe(4);
});

Run tests:

bun test

No additional frameworks required.

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Bundling with Bun

Bun also works as a bundler.

Example:

bun build index.ts --outdir=dist

This bundles your project for production.

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Best Practices for Using Bun

To get the most from Bun, follow these practices.

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1. Use Bun for Development Tooling

Bun works extremely well for:

• CLI tools
• development servers
• local utilities
• build scripts

It can replace many Node-based tooling scripts.

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2. Start Small

If you're migrating from Node.js, start with:

• side projects
• internal tools
• microservices

Avoid migrating large production systems immediately.

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3. Use Bun with Modern Frameworks

Many frameworks already support Bun.

Examples include:

• Next.js
• Vite
• SvelteKit

Bun can run development servers faster.

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4. Use Built-in Features First

Instead of installing extra libraries:

Use Bun’s built-in tools:

• testing
• bundling
• server runtime

This keeps your stack simpler and faster.

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5. Keep Compatibility in Mind

Although Bun supports most Node packages, some Node APIs may behave differently.

Before adopting Bun in production:

• test dependencies
• check compatibility
• review build tools

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When Should You Use Bun?

Bun is excellent for:

• new JavaScript projects
• backend APIs
• developer tooling
• TypeScript applications
• high-performance scripts

It may not yet be ideal for:

• legacy Node projects
• systems depending on complex Node APIs

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Bun vs Node.js (Quick Comparison)

Feature	Bun	Node.js
Runtime	JavaScriptCore	V8
Package Manager	Built-in	npm/yarn
Bundler	Built-in	External tools
Test Runner	Built-in	Jest/Mocha
Speed	Very fast	Stable but slower

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Final Thoughts

Bun represents a new direction in the JavaScript ecosystem.

Instead of combining many tools, Bun provides a fast, unified developer experience.

For developers building modern applications with TypeScript, APIs, and tooling, Bun can significantly simplify your workflow while improving performance.

If you haven’t tried it yet, Bun is definitely worth exploring.

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