Why I Switched from Node.js to Bun for JavaScript and TypeScript Development

The Status Quo

I've used Node.js since version 8. It's reliable, battle-tested, and runs practically everything. But over the years, the JavaScript toolchain has become a sprawling collection of separate tools:

• nvm to manage Node versions
• npm or yarn or pnpm for package management (each with its own lockfile format)
• tsc or esbuild or swc for TypeScript compilation
• jest or vitest or mocha for testing
• webpack or vite or esbuild or rollup for bundling

That's five different tools just to write and run JavaScript. Each one needs configuration, updates, and debugging.

Enter Bun - a single binary that replaces all of them.

What is Bun?

Bun is a JavaScript runtime, package manager, test runner, and bundler - all in one binary. It's written in Zig and built on top of JavaScriptCore (the engine Safari uses), not V8.

This matters because:

• Startup is faster - JavaScriptCore is optimized for quick cold starts
• Native TypeScript - Bun runs .ts and .tsx files directly, no compilation step
• Built-in test runner - compatible with Jest's API, no jest.config.js needed
• Native bundler - replaces webpack, esbuild, or rollup for most projects
• npm-compatible - reads package.json and node_modules just like npm

What I Actually Use Day to Day

Running TypeScript Without a Build Step

This alone was worth the switch:

bun run index.ts

No tsconfig.json required. No tsc --watch in another terminal. No ts-node or tsx. Bun transpiles TypeScript on the fly - including import paths, decorators, and JSX.

For this blog's CSS pipeline, I just run:

bun run css:build

Which kicks off tailwindcss -i ./static/css/input.css -o ./static/css/style.css. It just works.

Package Management - Significantly Faster

I won't quote benchmarks (everyone does), but the difference is noticeable. Installing dependencies with bun install is roughly 4-10x faster than npm install. The lockfile (bun.lock) is smaller and faster to parse.

For this blog, I switched from:

npm install
# ... 15 seconds of waiting

to:

bun install
# ... less than 2 seconds

On bigger projects (100+ dependencies), the gap widens.

The Built-in Test Runner

This might be my favorite feature. Bun ships a test runner that's Jest-compatible without any configuration:

// No imports needed - describe, it, expect are globals
describe('my function', () => {
  it('returns the correct value', () => {
    const result = myFunction();
    expect(result).toBe(42);
  });
});

bun test
# 1 pass, 0 fail - in 12ms

No Jest installation. No jest.config.ts. No @types/jest. No ts-jest transform. It just works.

Replacing nodemon

Bun has a built-in --watch flag:

bun --watch index.ts

This replaces nodemon for most of my projects. When a file changes, Bun restarts instantly because the cold start is so fast.

What About Ecosystem Compatibility?

This is the question everyone asks. Here's my experience:

• Express/Fastify/Koa - work fine
• Prisma - has native Bun support via prisma-client (with some caveats around the engine binary)
• Tailwind CSS - works perfectly (this blog uses it)
• Next.js - support is improving but not production-ready for most use cases yet
• Node.js built-in APIs - Bun implements most of them (fs, path, http, crypto, etc.)

There are gaps. Some packages that use native Node.js addons (node-gyp, node:worker_threads in specific patterns) don't work. But for the vast majority of web development, tooling, and scripting - Bun just works.

What I Still Use Node.js For

• Serverless deployments - Lambda and Cloud Functions are Node.js-first
• Legacy projects - I don't migrate projects that already work
• Specific native addon packages - anything that depends on node-gyp compiled binaries
• CI/CD systems - GitHub Actions runners have Node pre-installed, not Bun

Should You Switch?

Yes, if:

• You write TypeScript and want zero configuration
• You're tired of slow npm install times
• You want a single tool instead of 5+
• You build scripts, CLIs, backend APIs, or static sites

Maybe not, if:

• You depend on obscure Node.js native modules
• You need exact process isolation of Node.js Workers
• You're deploying to serverless environments that only support Node.js

The Bottom Line

Bun replaced 4 separate tools for me (npm, ts-node, jest, nodemon) with one binary. My development loop is faster, my configuration files are fewer, and I spend less time waiting for tools and more time writing code.

I still keep Node.js installed for the things Bun can't do yet. But for my daily work - writing TypeScript, building this blog, running scripts, and testing - Bun is my default.