Bun vs Node.js vs Deno

A year ago, choosing a JavaScript runtime wasn't a decision. You used Node. That was it. Today there are three real options, and they represent three genuinely different opinions about what running JavaScript outside the browser should be. I've built projects on all three this year, and here's what the choice actually comes down to.

The short version

| Runtime | What it's for | Who should pick it | |---|---|---| | Node.js | Stability and ecosystem | Anything that must run for years, with a team that will change | | Deno | Security and web standards | Untrusted code, strict environments, security-first teams | | Bun | Speed and developer experience | New projects where you control the whole stack |

There's no best runtime. There's only the one that matches your constraints, and the three have very different failure modes.

Node.js: the boring choice, and proud of it

Node wins on the only metric that matters for production software you'll maintain for a decade: it's everywhere. Every hosting platform supports it natively. Every package works with it. When a new developer joins your team in three years, they'll already know it.

That reliability is the flip side of its age. Getting a modern TypeScript project running still means assembling several tools, and the CJS/ESM split keeps tripping people up in 2026. Node's module story is a maze that everyone has learned to navigate rather than a design anyone defends.

Pick Node when longevity and ecosystem matter more than startup time or developer glee. For most companies, that's most of the time.

Deno: the one that respects the principle of least privilege

Deno is Ryan Dahl's do-over — a chance to fix the things he regretted about Node. The defining difference is architectural: Deno runs in a sandbox by default. Want file access? --allow-read. Network? --allow-net. Nothing gets access implicitly.

As someone who studies security, this is the runtime I find most interesting. A dependency in a Node app can silently read your files and phone home; in Deno, it literally cannot — the permission was never granted. That's not a feature, that's a different security model, and it's the correct one for running anything you don't fully trust.

The cost is friction. Flag-typing during development gets old, the ecosystem is smaller, and npm compatibility — while dramatically better than it used to be — still isn't complete.

Pick Deno when you're running untrusted code, or when least-privilege is a hard requirement rather than a nice-to-have. If your threat model says "assume every dependency is hostile," Deno is the only runtime built for that assumption.

Bun: what happens when speed is the whole pitch

Bun decided that JavaScript tooling should be fast — not incrementally, fundamentally — and it delivers. Install finishes before you can blink. Cold starts are in the low milliseconds. And because it bundles a runtime, package manager, bundler, and test runner into one binary, the tooling tax that Node quietly charges on every project just disappears.

The trade-offs are the predictable ones for something this young: some Node APIs still have gaps, and the ecosystem hasn't accumulated the same battle scars. When you hit an edge case, the answer might genuinely not exist yet.

Pick Bun when you're starting something new and you control the stack — which, for a student building side projects, is most of the time. It's what I use for personal work now, and the install speed alone made me stop reaching for npm.

What I'd tell my past self

For a long-lived production service with a team that will turn over: Node, and don't feel clever about it. For anything involving untrusted code or hard security requirements: Deno, and eat the friction — it's the friction doing its job. For new projects where you just want to build: Bun, and enjoy it.

Node proved JavaScript belongs on the server. Deno proved it can run there securely. Bun proved it can be fast without compromise. The real improvement is that picking a runtime is now a decision you get to make — and each option forces you to say what you actually value before you start.