Bun vs. Deno in Production: What I Wish I Knew Before
JavaScript runtimes are having a bit of a glow-up. If you’ve been stuck in the Node.js matrix like most of us, it’s hard to ignore the buzz around Bun and Deno. They both sound sleek, both promise something fresher—and both gave me a headache when I tried to run them in production.
After months of testing them in real-world apps (think actual users, not "hello world" demos), I’ve seen the good, the bad, and the missing documentation.
This post isn’t a cheerleader for either. It’s what I wish someone had told me before I deployed my first Bun or Deno service to production.
So... What Are Bun and Deno Really?
Before I dive into benchmarks and battle scars, a quick sanity check.
Deno is the brainchild of Ryan Dahl—you know, the same guy who built Node.js and then gave a talk titled “10 Things I Regret About Node.js.” Deno is his reimagined do-over: secure by default, ES modules-first, no more npm install bloat for every tiny feature. It includes a linter, formatter, and test runner. You can think of it as a minimalistic, TypeScript-native toolbelt.
Bun? Bun feels like someone locked a JavaScript engine in a lab with too much caffeine and said, “Go.” It runs on JavaScriptCore (yep, the engine behind Safari), and it comes with everything: bundler, transpiler, test runner, and its own npm-compatible package manager. It’s not just fast—it’s absurdly fast.
If you're still wrapping your head around how npm works under the hood, this breakdown on the Node Package Manager clears up a lot.
⚡ Startup Time: Blink and You’ll Miss It
In serverless contexts or anything that relies on cold starts, startup time matters. A lot.
Bun boots faster than I can say “callback hell.” We’re talking milliseconds here. It’s basically the Usain Bolt of JavaScript runtimes. I tested a simple function deployed on AWS Lambda, and Bun consistently outpaced Deno, shaving off precious time on every cold start.
Deno isn’t sluggish by any means, but it’s noticeably slower on spin-up. Think of it more like a reliable hybrid—efficient, but not in a hurry.
Throughput & Speed: Bun Leaves Tire Marks
When I stress-tested APIs under high concurrency, Bun ate the load for breakfast. Lower latency. Higher requests per second. And this wasn’t just anecdotal—it lined up with benchmarks published by the Bun team, especially in scenarios where I’d normally consider scaling horizontally.
That said, Deno shines in TypeScript-heavy codebases. If your app leans heavily on type safety and you’re tired of wrestling with tsconfig, Deno makes life easier—at the cost of a few RPS.
Security: Deno Babysits You (In a Good Way)
I once shipped a Node.js app to production with wide-open file system access. Learned that the hard way.
Deno protects you from these mistakes. It ships with a permission model that locks down access by default. Want to read a file? You have to opt in. Need network access? Explicitly allow it. It’s the kind of guardrail that saves you when you’re moving fast.
Bun, on the other hand, gives you all the rope. It’s up to you to build the safety net: container isolation, firewalls, runtime flags. No security theater here—just raw power and a warning label.
For devs just starting out, it’s easy to fall into traps if you skip foundational skills. Knowing how to use DevTools for debugging early can save a lot of production grief later.
📦 npm Compatibility: Bun Wins by a Mile
If your project has more dependencies than a Netflix show has plot twists, you’ll want Bun. It runs most npm packages right out of the box—including those pesky ones still clinging to CommonJS.
I ported a medium-sized Node.js app to Bun and only had to adjust two libraries. That’s unreal. The Bun team clearly prioritized compatibility, and it shows.
Deno has improved with npm specifier support, but things still break. You’ll find yourself wrapping libraries or rewriting utilities just to get past import errors. It’s improving—but it’s not seamless.
Developer Experience: Speed vs. Sanity
Let’s be real: you’re going to spend a lot of time with your runtime’s tooling. Might as well enjoy it.
Deno is boring in the best way. Linting, formatting, testing—it’s all included. No juggling a bunch of CLI tools. It’s like buying a car and finding out it came with free maintenance for life.
Bun is the opposite: raw power, but you’ll occasionally feel like you’re beta testing. Its CLI tools are fast—blazingly so—but error messages and docs haven’t always caught up. Still, if you’ve worked with tools that feel brittle or clunky, you’ll appreciate the attention to clean code practices that keep your stack maintainable.
Scaling: Not Just for Side Projects
Horizontal scaling is Bun’s home turf. Fast boot times and solid concurrency make it a beast for microservices. In my own Kubernetes setup, Bun containers scaled and stabilized faster than their Deno counterparts.
For vertical scaling, both support multithreading via native worker threads or subprocesses. But let’s be honest—Node.js, with its decade-plus of ecosystem maturity (and production-ready clustering tools), still has the crown here. Bun and Deno are playing catch-up, and they know it.
So… Should You Use Bun or Deno?
Here’s the blunt answer:
Use Bun if:
- You crave raw speed and instant startup.
- npm compatibility matters.
- You’re building from scratch and love working close to the metal.
- You don’t mind keeping one eye on the docs and the other on error logs.
Use Deno if:
- You value security and want built-in guardrails.
- TypeScript is your religion.
- You prefer all-in-one developer experiences without gluing tools together.
- You’re okay rewriting a few libraries for module compatibility.
Final Thoughts: Runtimes Are Tools, Not Tribes
I've used both in production. I still do.
For internal tools, rapid prototyping, and serverless endpoints, I lean hard into Bun. It’s fun, fast, and gets out of my way. But when I’m shipping something that touches sensitive data or sits behind auth walls, Deno’s defaults give me peace of mind.
Whatever you pick, don’t forget to run real-world tests with traffic. Benchmarks are cute, but production is mean. And nothing humbles you faster than a server that croaks under pressure at 3AM.