Bun vs Node.js vs Deno: Which One Actually Doesn't Suck?

Here's the thing about JavaScript runtime benchmarks: they're mostly synthetic garbage that has fuck-all to do with your actual app. But the numbers are still useful if you know how to read them without drinking the performance Kool-Aid.

These Tests Run on Monster Servers You Don't Have

The TechEmpower benchmarks run on absolute beast machines - Intel Xeon with 32 cores and 32GB RAM. That's way beefier than your MacBook Pro or that AWS t2.micro you're running your side project on.

Reality Check on Test Environment:

• 32 cores (your laptop has 8 if you're lucky, and 4 are thermal throttling)
• 32GB RAM (your production server probably has 4GB and Slack is using 2GB)
• 10Gbps dedicated network (your Docker containers are fighting over 100Mbps)
• Multiple load generators (you'll ab -n 1000 and call it testing)
• 15-minute tests with warmup (users close the tab after 3 seconds)

Bun Absolutely Annihilates Node.js (But There's Always a Catch)

Performance Comparison (Requests per Second - tested on identical hardware):

Bun v1.2.21:      ████████████████████████ 68,000
Deno v2.4.5:      ████████████ 29,000  
Node.js v22.19.0: ████████ 14,000

The raw numbers are brutal for Node.js: Bun hits 68,000 requests per second while Node.js with Express manages a pathetic 14,000. That's nearly 5x faster. If you're still using Express and wondering why your API feels sluggish, this should hurt.

Deno sits in the middle at 29,000 requests per second, which is respectable but not earth-shattering. When you bump up the concurrency, Bun hits 110,000 requests per second - at this point Node.js looks like it's running on a potato.

Why Bun is so damn fast: It's built on JavaScriptCore (Safari's engine) instead of V8, and their HTTP server is written in Zig, not JavaScript. Meanwhile, Node.js is still dragging around decades of legacy bullshit that makes everything slower than it needs to be.

Your AWS Bills Will Thank You

Cold Start Performance:

• Bun: 50-80ms startup ⚡
• Node.js: 150-200ms startup 🐌
• Deno: 120-180ms startup

Node.js is a memory hog. I learned this the hard way when our production server kept running out of memory every few hours with this lovely error: JavaScript heap out of memory. Spent a whole weekend debugging what turned out to be event listeners that never got cleaned up. Bun uses 3x less memory than Node.js for the same workload, which means fewer 3am pages about OOM crashes.

The numbers are real: in production, switching to Bun saves 20-30% on memory usage. That translates to actual dollars when you're running containerized apps that need less RAM per pod.

Why Node.js eats so much memory: It's carrying around a bunch of legacy crap for backwards compatibility. Every Buffer gets duplicated, every string gets converted multiple times, and V8's garbage collector is complex as hell. Bun stripped out all that cruft.

npm install Takes Forever and Breaks Randomly

The most painful part of Node.js development? Waiting for npm install to finish while your CPU fan sounds like a jet engine. It takes 2 minutes on a good day, and half the time it fails with some cryptic EACCES: permission denied error or ETIMEOUT bullshit.

Bun install finishes in 8 seconds for the same packages that take npm 120 seconds. That's not just a little faster - that's life-changing for your development workflow. CI/CD pipelines that took 5+ minutes now finish under 2 minutes.

Cold start times matter for serverless: Bun boots in 50-80ms, Node.js takes 150-200ms. If you're running AWS Lambda, faster cold starts mean 30-50% lower bills for short functions. Check out serverless performance optimization tips.

These Benchmarks Don't Mean Shit if Your App is Database-Bound

Here's the reality check nobody talks about: real-world testing with JWT validation, PostgreSQL queries, and PDF generation shows Bun only 37% faster than Node.js, not 5x.

Why? Because your app spends most of its time waiting for the database to return results, not parsing HTTP requests. When PostgreSQL takes 50-200ms to execute a query, the runtime's 1-5ms overhead becomes irrelevant.

The real performance bottlenecks in your app:

• Database queries that don't use indexes properly
• External API calls with 100ms+ latency
• File system operations that block the event loop
• JSON parsing for massive payloads
• Image processing or other CPU-heavy tasks

If you're database-bound, optimize your queries with `EXPLAIN ANALYZE` before switching runtimes. If you're API-bound, add Redis caching. The 3x performance gains from switching to Bun only matter if JavaScript execution is actually your bottleneck.

So where do these impressive numbers come from? Let's break down the actual performance data...

![Runtime Architecture Comparison](https://images.ctfassets.net/aq13lwl6616q/5d

NJ6fFbGeeOnWIxPhZyW6/933b2363c3b6ccfc1987ad6ad735eef0/usage_data.jpg)

Look, the benchmarks are impressive, but let me tell you what actually happens when you try to migrate a real production app.

Spoiler: it's not all rainbows and 5x performance gains.

Bun Breaks Half Your npm Packages

The reality nobody talks about: Bun uses Java

ScriptCore (Safari's engine) instead of V8, which means a bunch of npm packages that rely on V8 internals will shit the bed.

I learned this the hard way when our image processing library crashed with this helpful error: `TypeError:

Cannot read property 'byteLength' of undefined. Spent 3 hours debugging what turned out to be missing ArrayBuffer` methods.

What actually broke in our migration:

• `sharp` (image processing)
• threw `Error:

Cannot read property 'data' of null`, needed different build

• `sqlite3`
• native bindings failed with gyp ERR!, had to switch to `better-sqlite3`
• `bcrypt`
• segfaulted randomly (fun!), replaced with `bcryptjs`
• Custom webpack configs
• some plugins assume V8 behavior, broke with cryptic errors

Node.js V8 has decades of cruft but at least everything works. V8's garbage collector causes random 50-200ms pauses when it decides to clean house, but it's predictable. JavaScriptCore is faster to start but occasionally does weird shit with memory allocation.

Deno's security model is annoying as hell until you actually get hacked.

Every file read requires `--allow-read`, every network call needs `--allow-net`.

It's secure by default, but your startup script becomes a mess of permissions flags.

Express is a Performance Disaster

Express.js Request Flow:

Request → Body Parser → CORS → Auth → Logger → Your Code → Response
         ↓ allocates  ↓ adds   ↓ JWT  ↓ writes ↓ finally!
         objects     headers   check  to disk  some business logic

Here's why your Express API is slow: Every request goes through 15 layers of middleware bullshit.

Body parsing, CORS, logging, auth, validation

• each one allocating objects and calling functions. Bun's native HTTP server skips all that and handles requests in Zig code, not JavaScript.

The Express middleware tax:

• `body-parser`
• converts your JSON 3 times
• `helmet`
• adds security headers you probably don't need
• `morgan`
• logs every request even in production
• `cors`
• allows every origin because you forgot to configure it
• Your custom middleware
• because you love reinventing wheels

**Fastify is better than Express** but still nowhere near Bun's native performance.

At least it doesn't serialize/deserialize JSON multiple times per request.

Deno's HTTP story is confusing

• they have like 4 different ways to create servers, and the docs assume you already know which one to use.

The performance is decent but the APIs keep changing between versions.

Memory Leaks Will Ruin Your Weekend

Typical Node.js Memory Pattern:

Memory Usage Over Time:
100MB ████████████████████████████████████████████████
 80MB ████████████████████████████████████████
 60MB ████████████████████████████
 40MB ████████████████
 20MB ████████
   0h    2h    4h    6h    8h → OOM crash at hour 8

Node.js memory usage grows like cancer if you're not careful.

Lost a weekend to this shit when I found like 800+ Event

Emitter listeners that never got cleaned up, all because someone forgot to call removeListener(). The --inspect flag and Chrome DevTools help, but good luck explaining heap snapshots to your manager who just wants to know why the server crashed at 3am.

Common memory leak culprits:

• Event listeners that never get removed
• Timers that keep running after components unmount
• Circular references in closures
• Massive JSON objects that never get garbage collected
• Database connection pools that don't close properly

Bun's memory advantage is real

• same app uses 3x less RAM.

But debugging memory issues in Bun is harder because fewer tools support Java

ScriptCore profiling. When it breaks, you're basically screwed.

Deno's Rust code doesn't leak memory like JavaScript does, which is nice until you realize your TypeScript still leaks memory and now you have two different memory models to debug.

The Bottom Line: When to Actually Switch

Don't migrate just for the benchmarks. I've seen teams spend 6 months migrating to Bun for a 20% performance improvement they could have gotten by adding a Redis cache.

Switch to Bun if:

• Your app is CPU-bound (rare for most web apps)
• You're building a new project and can handle the ecosystem gaps
• Package installation time is killing your CI/CD pipeline
• You're running serverless functions where cold start matters

Stick with Node.js if:

• You have complex native dependencies
• Your team doesn't have time to debug obscure runtime issues
• You're database-bound (most web apps)
• You need the mature tooling ecosystem

Try Deno if:

• You're building a secure CLI tool or edge function
• You love Type

Script and hate build steps

• You enjoy fighting with import URLs and permission flags

The 5x performance gains in benchmarks become 10-30% in production, if you're lucky. Optimize your database queries first, add caching second, then maybe consider switching runtimes third.

**Now, if you're still determined to run performance tests, here's how to do it without misleading yourself...