Bun: Can It Really Replace Node.js?

npm install Taking 3 Minutes, Now Takes 10 Seconds

I cloned a project and ran npm install. Time to grab a coffee. Three minutes. On days with heavy dependencies, it would take over 5 minutes. Then I tried Bun and it finished in 10 seconds. At first, I thought something went wrong. "Did it actually install everything?" I checked package.json, opened the node_modules folder, and ran the project before I believed it.

It's fast, I get that. But can I use it in production? Is it compatible with the Node.js ecosystem? Can I deploy it to production safely? These questions kept piling up.

Bottom line: Bun wasn't just "fast Node.js". It was an all-in-one toolkit combining runtime, bundler, package manager, and test runner. Like a Swiss Army knife. And it actually worked in most cases.

The Realization: Bun Is a Platform, Not an Ecosystem

Initially, I thought of Bun as a "faster alternative to npm". Wrong. Bun was a complete redesign of the entire JavaScript development experience.

What did you need to start a project in Node.js? Manage packages with npm or pnpm, bundle with esbuild or webpack, test with Jest or Vitest, run dev server with nodemon or tsx... Each tool required its own config file.

Bun unified all of this. And much faster. Like switching from carrying luggage in multiple bags, one at a time, to packing everything in one large trunk and moving it all at once.

The Secret to Speed: Zig and JavaScriptCore

Node.js is written in C++ and uses the V8 engine. Bun is written in Zig and uses JavaScriptCore (Safari's engine). This difference translated into noticeable speed.

# Node.js project
$ time npm install
real    3m 12s

# Same project with Bun
$ time bun install
real    0m 9s

20 times faster. It wasn't just package downloads. Server startup, test execution, bundling—all faster.

What Bun Really Is: Four Tools Unified

1. Runtime: Node.js Compatible + Native APIs

Bun supports most Node.js APIs. Basic modules like fs, path, http work as-is. Most existing Node.js projects run without modification.

But Bun's native APIs were the real game-changer.

// Node.js way
import express from 'express';
const app = express();
app.get('/', (req, res) => res.send('Hello'));
app.listen(3000);

// Bun native way
Bun.serve({
  port: 3000,
  fetch(req) {
    return new Response('Hello');
  },
});

Bun.serve() starts an HTTP server without express. And much faster. Benchmarks showed request throughput 3x higher than Node.js + Express. Fewer dependencies, better performance—win-win.

File I/O was more intuitive too.

// Node.js way
import fs from 'fs/promises';
const text = await fs.readFile('file.txt', 'utf-8');
const buffer = await fs.readFile('image.png');

// Bun way
const file = Bun.file('file.txt');
const text = await file.text();
const buffer = await file.arrayBuffer();

Bun.file() provides native File API support. You can write it like browser code, which felt familiar. Plus, SQLite is built-in.

import { Database } from 'bun:sqlite';

const db = new Database('mydb.sqlite');
db.run('CREATE TABLE IF NOT EXISTS users (id INTEGER PRIMARY KEY, name TEXT)');
db.run('INSERT INTO users (name) VALUES (?)', 'Alice');
const users = db.query('SELECT * FROM users').all();

No package installation needed—SQLite works out of the box. Super convenient for prototyping.

2. Package Manager: 20x Faster Than npm

bun install is compatible with npm, yarn, and pnpm. It uses the same package.json but runs much faster.

bun install                    # Install from package.json
bun add express               # Same as npm install express
bun add -d typescript         # Add to devDependencies
bun remove lodash             # Remove package

The lockfile is different. bun.lockb uses a binary format. It reads and writes much faster than text-based lockfiles. Git diffs don't make sense for it, but honestly, who carefully reviews lockfile diffs anyway?

The global cache was smart. When the same package is used across multiple projects, it creates hard links to save disk space. Similar to pnpm's approach, but faster.

3. Bundler: esbuild Speed with Zero Config

bun build ./src/index.ts --outdir ./dist

That's it. No config file needed—bundling just works. TypeScript, JSX, CSS—all handled automatically.

// For advanced configuration
await Bun.build({
  entrypoints: ['./src/index.ts'],
  outdir: './dist',
  minify: true,
  sourcemap: 'external',
  splitting: true, // code splitting
  target: 'browser',
});

As fast as esbuild but simpler to configure. Switching from webpack felt like deleting 200 lines of config.

4. Test Runner: Jest Compatible, Much Faster

// math.test.ts
import { expect, test, describe } from 'bun:test';

describe('Math', () => {
  test('addition', () => {
    expect(1 + 1).toBe(2);
  });

  test('async operation', async () => {
    const result = await Promise.resolve(42);
    expect(result).toBe(42);
  });
});

Nearly identical to Jest's API. Existing test code works almost as-is. But the speed difference was huge.

# Jest
$ time npm test
Tests: 156 passed
Time: 8.3s

# Bun
$ time bun test
Tests: 156 passed
Time: 0.7s

Over 10 times faster. This difference really showed in watch mode. Save code, get test results instantly.

Compatibility: Most Things Work, Some Don't

Bun aims for Node.js ecosystem compatibility, but it's not 100%.

Works well:

• Web frameworks like Express, Fastify
• ORMs like Prisma, Drizzle
• Validation libraries like Zod, Yup
• Most utility libraries (lodash, date-fns, etc.)

Occasional issues:

• Packages using native addons (bcrypt, sharp, etc.)
• Packages deeply dependent on Node.js internals
• Some older packages

I migrated a few projects: 80% worked out of the box, 15% needed minor tweaks, 5% required finding alternative packages.

Like switching from Windows to Mac. Most apps are available, but occasionally you'll find one that isn't.

When to Use Bun: New Projects First

Perfect use cases for Bun:

1. New projects

• Start without legacy constraints
• Modern packages mostly work with Bun
• Development speed is overwhelmingly fast

2. CLI tools and scripts

#!/usr/bin/env bun
// deploy.ts
const response = await fetch('https://api.service.com/deploy', {
  method: 'POST',
  body: await Bun.file('./dist.zip').arrayBuffer(),
});
console.log(await response.json());

I converted Node.js scripts to Bun and execution speed doubled or tripled. Fast cold starts make the difference.

3. Development tooling

• Local dev servers
• Build pipelines
• Test environments

When NOT to use Bun yet:

1. Enterprise production

• Limited time in production (1.0 released September 2023)
• Fewer references when issues occur
• High risk if entire team is familiar with Node.js

2. Cases requiring native addons

• Image processing (sharp)
• Encryption (native bcrypt)
• Specific hardware control

In these cases, stick with Node.js or isolate those features into separate services.

Migration: Easier Than Expected

I actually migrated a Next.js project to Bun.

# 1. Install Bun
curl -fsSL https://bun.sh/install | bash

# 2. Delete node_modules and reinstall
rm -rf node_modules
bun install

# 3. Run
bun run dev

That was it. Most cases just worked.

For problematic packages:

// package.json
{
  "dependencies": {
    // "bcrypt": "^5.1.0",  // Uses native addon
    "bcryptjs": "^2.4.3"    // Replace with pure JS implementation
  }
}

Swap in pure JavaScript implementations. Slight performance hit, but not a problem in development.

For production? Still approached cautiously. Tried it first on new microservices or side projects. If they ran without issues, gradually expanded. Incremental strategy.

The Bottom Line

Bun wasn't about answering "Can it replace Node.js?" but rather "How can we improve the JavaScript development experience?"

Instead of learning and configuring npm, webpack, Jest, nodemon separately, you can do everything with one unified tool. And much faster.

Starting a new project? I'd use Bun. Migrating an existing project? I'd weigh the risks. Production deployment? I'd start small and experiment.

Being fast wasn't just about saving time. It was about maintaining flow. Not doing other things while tests run. Not losing focus waiting for bundling.

Bun was a tool that respected developers' time. And that's ultimately the starting point for building better software.