I switched our teamā€™s development environment to Bun eight months ago, and three months later we started running it in production. The results have beenā€¦ complicated. Not ā€œBun is amazing and Node is deadā€ complicated, but ā€œthe right tool depends on what youā€™re buildingā€ complicated.

Let me share the real story ā€” benchmarks, compatibility issues, what broke, and what worked beautifully.

The Current State of Bun (Mid-2025)

Bun has matured significantly since its 1.0 release. When I first tried it in late 2023, it was fast but broke half my dependencies. Now in 2025, compatibility is genuinely good ā€” Iā€™d estimate 95%+ of the npm ecosystem works without issues.

But hereā€™s what most comparison articles wonā€™t tell you: the biggest productivity gain from Bun isnā€™t runtime speed ā€” itā€™s the all-in-one toolchain.

Why I Gave Bun a Serious Shot

Our stack before the switch:

  • Node.js 20 (runtime)
  • npm (package manager)
  • Jest (testing)
  • tsx (TypeScript execution)
  • webpack/esbuild (bundling)
  • dotenv (environment variables)
  • nodemon (file watching)

With Bun, this entire list collapses into one binary. Thatā€™s not a minor convenience ā€” itā€™s fewer dependencies, fewer config files, and fewer things that break.

Installation & Developer Experience

# Install Bun (macOS/Linux)
curl -fsSL https://bun.sh/install | bash

# Or with Homebrew
brew install oven-sh/bun/bun

# Check version
bun --version  # 1.1.38 as of writing

First-Run Experience

# Initialize a new project
bun init

# Install dependencies (from existing package.json)
bun install  # ~0.8 seconds for a project with 1,200 deps

# Compare with npm
npm install  # ~18 seconds for the same project

That 22x speed difference in package installation isnā€™t a cherry-picked benchmark ā€” itā€™s consistent across every project Iā€™ve tested. And it makes a massive difference in CI/CD pipelines.

Pro Tip: If youā€™re using GitHub Actions, switching from npm install to bun install can cut your CI times by 2-3 minutes per run. That adds up to hours saved per week across a team.

Real-World Benchmarks

I benchmarked both runtimes on our actual production workloads, not synthetic ā€œhello worldā€ servers. Hereā€™s what I found:

HTTP Server Performance

Test: Simple REST API with JSON serialization, database query (PostgreSQL), and response formatting.

Metric Node.js 22 Bun 1.1 Difference
Requests/sec (simple JSON) 48,200 91,500 +90%
Requests/sec (DB query) 12,400 14,800 +19%
Requests/sec (complex logic) 8,200 9,100 +11%
P99 Latency (simple) 2.1ms 1.1ms -48%
P99 Latency (DB query) 18ms 16ms -11%
Memory (idle) 45MB 32MB -29%
Memory (under load) 180MB 120MB -33%
Startup time 320ms 45ms -86%

The Reality Check

Notice how the performance gap shrinks dramatically once you add real-world operations like database queries? Thatā€™s because in most applications, the bottleneck isnā€™t the JavaScript runtime ā€” itā€™s I/O operations, database queries, and network calls.

The honest truth: If your API spends 80% of its time waiting on PostgreSQL queries, switching from Node to Bun gives you maybe 10-15% improvement in total throughput. Still nice, but not life-changing.

Where Bunā€™s speed really matters:

  • Startup time (serverless/Lambda functions)
  • CPU-intensive tasks (parsing, serialization, crypto)
  • Package installation (CI/CD pipelines)
  • Test execution

Test Execution Speed

This is where Bun genuinely blew me away:

# Running our test suite (847 tests)
# Node.js + Jest
npx jest  # 34.2 seconds

# Node.js + Vitest
npx vitest run  # 12.8 seconds

# Bun's built-in test runner
bun test  # 4.1 seconds

Pro Tip: Even if you donā€™t switch your production runtime to Bun, consider using bun test for development. The speed improvement makes TDD actually enjoyable. Your tests can still target Node.js for CI ā€” most well-written tests are runtime-agnostic.

TypeScript Support: Zero Config

This is my favorite Bun feature. No ts-node, no tsx, no tsconfig paths configuration needed:

# Just run TypeScript directly
bun run src/server.ts

# No compilation step, no source maps config, just works
// src/server.ts - runs directly with `bun run src/server.ts`
import { serve } from 'bun';

const server = serve({
  port: 3000,
  fetch(req) {
    const url = new URL(req.url);
    if (url.pathname === '/health') {
      return Response.json({ status: 'ok', runtime: 'bun' });
    }
    return new Response('Not Found', { status: 404 });
  },
});

console.log(`Server running at http://localhost:${server.port}`);

Compare this to the Node.js equivalent:

// Node.js requires additional setup:
// 1. Install: tsx or ts-node
// 2. Configure: tsconfig.json with proper module settings
// 3. Run: npx tsx src/server.ts

import express from 'express';
const app = express();

app.get('/health', (req, res) => {
  res.json({ status: 'ok', runtime: 'node' });
});

app.listen(3000, () => {
  console.log('Server running at http://localhost:3000');
});

Package Management

Bunā€™s package manager is phenomenal. Hereā€™s a speed comparison on real projects:

Project Size npm install pnpm install Bun install
Small (50 deps) 8s 4s 0.4s
Medium (300 deps) 25s 12s 1.2s
Large (1200 deps) 65s 28s 3.1s
Monorepo (5000 deps) 180s 45s 8.2s

Cold cache, fresh install. All tested on M2 MacBook Pro.

Lockfile Compatibility

Bun uses its own bun.lockb (binary lockfile), but it can read package-lock.json and yarn.lock for migration:

# Migrate from npm - Bun reads package-lock.json automatically
rm -rf node_modules
bun install  # Creates bun.lockb, respects existing lock versions

Compatibility: What Works and What Doesnā€™t

After 8 months of production use, hereā€™s my compatibility report:

āœ… Works Perfectly

  • Express.js
  • Fastify
  • Prisma
  • Drizzle ORM
  • Zod
  • React/Next.js (with some caveats)
  • PostgreSQL drivers (pg, postgres)
  • Redis clients
  • Most testing libraries
  • GraphQL (Apollo, Yoga)

āš ļø Works with Minor Issues

  • Next.js (some edge runtime features differ)
  • Sharp (image processing ā€” needs native rebuild)
  • Puppeteer (use playwright instead)
  • Some native Node.js addons (C++ bindings)

āŒ Doesnā€™t Work / Not Recommended

  • node-gyp heavy packages (declining issue)
  • Some AWS SDK v2 features (use v3)
  • Certain Webpack plugins that rely on Node internals

Pro Tip: Before migrating, run bun install && bun test on your existing project. If tests pass, youā€™re probably good. The test suite is your best compatibility indicator.

Migration Guide: Node.js to Bun

Hereā€™s the exact process I followed for our production migration:

Step 1: Development Environment

# Install Bun alongside Node.js (they coexist fine)
curl -fsSL https://bun.sh/install | bash

# Try running your project
bun install
bun run dev  # or whatever your dev script is

# Run your test suite
bun test

Step 2: Update Scripts in package.json

{
  "scripts": {
    "dev": "bun run --watch src/index.ts",
    "start": "bun run src/index.ts",
    "test": "bun test",
    "build": "bun build src/index.ts --outdir ./dist --target node"
  }
}

Step 3: Replace Node.js-specific APIs

// Before (Node.js specific)
import { readFile } from 'fs/promises';
import { createServer } from 'http';

// After (works in both, but uses Bun's optimized APIs)
const file = Bun.file('./config.json');
const config = await file.json();

// Bun's native HTTP server
const server = Bun.serve({
  port: 3000,
  fetch(req) {
    return new Response('Hello!');
  }
});

Step 4: Docker Configuration

# Before: Node.js
FROM node:22-alpine
WORKDIR /app
COPY package*.json ./
RUN npm ci --production
COPY . .
CMD ["node", "dist/index.js"]

# After: Bun
FROM oven/bun:1.1-alpine
WORKDIR /app
COPY package.json bun.lockb ./
RUN bun install --frozen-lockfile --production
COPY . .
CMD ["bun", "run", "src/index.ts"]

The Bun Docker image is smaller (base ~80MB vs ~120MB for Node Alpine), and you skip the build step entirely since Bun runs TypeScript directly.

For more Docker optimization tips, check out our dedicated guide.

Built-in Features That Replace Dependencies

Feature Node.js Approach Bun Built-in
.env files dotenv package Native Bun.env
File watching nodemon/chokidar --watch flag
TypeScript ts-node/tsx Native execution
Testing Jest/Vitest/Mocha bun test
Bundling webpack/esbuild/rollup Bun.build()
SQLite better-sqlite3 bun:sqlite
Password hashing bcrypt Bun.password
HTTP client node-fetch/axios Native fetch

Thatā€™s easily 8-10 fewer dependencies per project. Fewer deps means fewer security vulnerabilities, faster installs, and less maintenance.

Common Mistakes When Switching to Bun

1. Assuming All Node.js Code Runs Unchanged

While compatibility is excellent, Bun implements Web Standard APIs (like fetch, Request, Response) natively. Code that monkey-patches these or relies on Node-specific polyfills may behave differently.

2. Not Testing Edge Cases

Bunā€™s event loop implementation differs from Nodeā€™s in subtle ways. If you have code that depends on specific process.nextTick or setImmediate ordering, test carefully.

3. Using Bun in Production Without Load Testing

Always load test with your production traffic patterns. I found one memory leak that only appeared under sustained concurrent connections in Bun that didnā€™t exist in Node. It was fixed in a subsequent Bun release, but the lesson stands.

4. Ignoring the Ecosystem Lock-in

bun.lockb is a binary format. If team members need to use npm/pnpm for any reason, they canā€™t read the lockfile. Consider keeping a package-lock.json in sync using bun install --save-lockfile.

5. Expecting Identical Behavior for Streams

Node.js Streams and Web Streams APIs have subtle differences. Bun prefers Web Streams. If your code heavily uses Node Streams (especially Transform streams), test thoroughly.

When to Use Bun vs Node.js

Choose Bun When:

  • Starting a new project (no migration cost)
  • Building serverless functions (startup speed matters)
  • Developer experience is a priority (all-in-one toolchain)
  • You want native TypeScript without a build step
  • CI/CD speed matters (faster installs + tests)

Stick with Node.js When:

  • You have heavy native C++ addon dependencies
  • Enterprise compliance requires LTS guarantees
  • Your team isnā€™t comfortable with newer runtimes
  • Youā€™re running in environments without Bun support
  • Stability is more important than speed

What About Deno?

For a complete picture, check out our Deno 2 features guide. The short version: Deno occupies a middle ground ā€” better Node.js compatibility than ever, but Bunā€™s speed advantage in raw I/O remains significant. Denoā€™s strength is security-first design and standards compliance.

My Verdict After 8 Months

Bun is my default for new projects. The developer experience is superior, the speed gains in tooling (not just runtime) are substantial, and compatibility has reached the point where I rarely encounter issues.

For existing Node.js projects? Migrate your development environment first (bun install, bun test, bun run dev). Get the DX benefits immediately. Production migration can wait until youā€™ve built confidence.

The JavaScript runtime landscape in 2025 is genuinely exciting. Competition between Node, Bun, and Deno is making all three better. We all win.

FAQ

Is Bun production-ready in 2025?

Yes, with caveats. Companies like Vercel, Figma, and numerous startups run Bun in production. For standard web APIs and backend services, itā€™s stable. For edge cases involving complex native modules or specific Node.js internals, test thoroughly. Iā€™ve had zero production incidents directly attributable to Bun in 8 months.

Can I use Bun with Next.js?

Yes, but with limitations. Bun works great as the package manager and for running Next.js in development. However, Next.js in production still uses its own runtime layer. For the best experience, use Bun for bun install and development, but deploy with the standard Next.js build output.

Does Bun support all npm packages?

About 95%+ of npm packages work without issues. The remaining 5% are typically packages with native C++ addons that havenā€™t been compiled for Bunā€™s runtime. This number keeps improving with each Bun release. Check the Bun compatibility tracker for specifics.

Should I switch from pnpm to Bun for package management?

If speed is your priority, yes. Bunā€™s package manager is 3-10x faster than pnpm in my benchmarks. However, pnpmā€™s strict dependency isolation (no phantom dependencies) is still superior. For monorepos, Iā€™d evaluate based on your teamā€™s needs ā€” pnpmā€™s strictness catches bugs that Bunā€™s hoisting approach might miss.

How does Bun affect bundle size for frontend apps?

Bunā€™s bundler (Bun.build()) produces comparable output sizes to esbuild (which makes sense, as they share design philosophies). For frontend bundling specifically, I still prefer Vite for its plugin ecosystem and dev server experience. Bun shines more as a backend runtime and dev toolchain.