If you’ve been working with JavaScript for any length of time, you know the setup pain. Installing dependencies, configuring TypeScript, setting up bundlers, choosing test runners: before you write a single line of application code, you’ve already made dozens of tooling decisions and configurations.

Bun aims to solve this problem by consolidating the JavaScript toolchain into a single, fast runtime.

The Traditional JavaScript Tooling Problem

A typical JavaScript project setup looks like this:

npm init -y
npm install react typescript @types/react
npm install -D vite jest @testing-library/react
npm install -D eslint prettier

Then you need to configure:

  • tsconfig.json for TypeScript
  • vite.config.js for bundling
  • jest.config.js for testing
  • .eslintrc for linting
  • package.json scripts to tie it all together

You end up with a node_modules folder with hundreds of megabytes of dependencies, multiple configuration files, and a fragmented workflow across different tools.

What Bun Provides

Bun is a JavaScript runtime built from the ground up with modern JavaScript development in mind. It includes:

  • Runtime: Executes JavaScript and TypeScript files natively
  • Package Manager: Installs npm packages significantly faster than npm/yarn
  • Bundler: Bundles code for production without additional configuration
  • Test Runner: Built-in testing framework with Jest-compatible API
  • Transpiler: Native TypeScript and JSX support, no configuration needed

All of this in a single binary called bun.

A Simpler Workflow

Here’s the same project setup with Bun:

bun create react ./my-app
cd my-app
bun run dev

That’s it. TypeScript works out of the box. JSX is transpiled automatically. Testing is available via bun test. No configuration files needed for basic usage.

Running TypeScript Directly

# No transpilation step needed
bun run app.ts

Bun executes TypeScript files directly without requiring a separate build step or ts-node.

💡 Why This Matters: Traditional Node.js requires either a compilation step (tsc) or runtime transpilation (ts-node, which adds overhead). Bun’s native TypeScript support means you can run .ts files as easily as .js files, eliminating the mental overhead of managing build pipelines during development.

Package Installation

bun install

Package installation is 10-30x faster than npm, thanks to Bun’s implementation in Zig and optimized dependency resolution.

💡 Why This Matters: Bun uses a global cache and parallel installation strategy. Instead of downloading the same package multiple times across projects, it shares dependencies intelligently. This isn’t just about speed: it saves disk space and makes context switching between projects nearly instant.

Testing

bun test

The built-in test runner is Jest-compatible, so most existing tests work with minimal changes:

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

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

Performance Characteristics

Bun’s implementation brings notable performance improvements:

  • Package Installation: 10-30x faster than npm/yarn
  • Cold Starts: Sub-20ms startup time, beneficial for serverless functions
  • Runtime Performance: Up to 4x throughput compared to Node.js in some benchmarks
  • Build Times: 50-70% reduction reported by teams migrating from webpack

These numbers vary by workload, but the consistent theme is faster iteration cycles during development.

💡 Understanding the Performance: Bun’s speed comes from three key decisions: (1) Written in Zig, a low-level language that compiles to efficient machine code, (2) Uses JavaScriptCore (Safari’s engine) instead of V8, which has faster startup times, (3) Implements system APIs natively rather than wrapping Node.js APIs. This isn’t just optimization, it’s architectural rethinking.

Real-World Adoption

Bun has gained traction with over 5 million monthly downloads. Notable users include:

  • Anthropic: Powers the Claude Code CLI
  • Vercel: Now offers native Bun runtime support
  • AWS Lambda, Cloudflare Workers: Serverless platforms supporting Bun

Companies like Brex and Linear use Bun in production for specific services.

When to Use Bun

Good fits:

  • New projects where you want faster setup and iteration
  • CLI tools that benefit from fast startup times
  • Serverless functions where cold start performance matters
  • Development environments, even if you deploy to Node.js

Consider Node.js for:

  • Existing production systems with established Node.js infrastructure
  • Projects heavily dependent on native npm modules with C++ bindings
  • Enterprise environments requiring extensive ecosystem maturity
  • When stability and predictability are prioritized over cutting-edge features

💡 The Migration Question: You don’t have to choose one or the other exclusively. Many teams use Bun locally for faster development iteration while deploying to Node.js in production. This hybrid approach gives you speed during development without production risk. Start with bun install and bun run locally: it’s a zero-risk way to experience the benefits.

Impact on the JavaScript Ecosystem

Beyond Bun itself, the project has created healthy competition in the JavaScript runtime space. Node.js 23 introduced several performance improvements and features that directly address pain points Bun solved first.

This competition benefits everyone:

  • Node.js is getting faster and more developer-friendly
  • Bun is maturing and improving compatibility
  • Developers have more choices for their specific use cases

Getting Started

Install Bun:

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

Try it on a new project:

bun create next-app ./my-next-app
cd my-next-app
bun dev

Or gradually adopt it in existing projects by using Bun for package installation while keeping Node.js for runtime:

bun install  # Faster package installation
node index.js  # Continue using Node.js runtime

Conclusion

Bun simplifies JavaScript tooling by consolidating the runtime, package manager, bundler, and test runner into a single, fast tool. It reduces configuration overhead, speeds up common development tasks, and provides a more streamlined developer experience.

Whether you adopt Bun fully or just use it for package management, it represents a step toward simpler, faster JavaScript development workflows.

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