JavaScript developers are currently caught in a messy, high-stakes tug-of-war. For a decade, Node.js was the undisputed king, the default choice, the boring-but-reliable engine under every enterprise app. Then Jarred Sumner dropped Bun into the ecosystem like a pipe bomb. Everyone saw the benchmarks. Bun is fast. Ridiculously fast. It makes Node look like it’s wading through waist-deep molasses. But here’s the thing nobody mentions in those flashy "Hello World" speed tests: moving to the Bun runtime is often a massive, headache-inducing pain in the neck for anyone with a real-world codebase.
Speed isn't everything.
If you are building a greenfield project, Bun feels like magic. You get a bundler, a test runner, and a package manager all in one binary. It’s sleek. It’s modern. But most of us aren't building "Hello World" apps. We are managing 500,000-line monstrosities with five-year-old dependencies and weird C++ addons that barely work on Node, let alone a brand-new engine written in Zig.
The Compatibility Lie (and Why It Hurts)
The marketing for the Bun runtime leans heavily on the idea of being a "drop-in replacement" for Node.js. That’s a bold claim. Honestly, it’s a bit of an exaggeration. Bun implements most of the Node API, sure. It handles fs, path, and http. But "most" is a dangerous word in software engineering. When you're dealing with low-level buffer manipulations or specific crypto implementations, "most" equals "broken production build."
Node.js has had fourteen years to iron out its quirks. It has a massive suite of regression tests. Bun is the newcomer. While it supports node_modules and CommonJS, the way it handles resolution can sometimes differ just enough to break a specific version of a niche library your team depends on.
I’ve seen developers spend three days debugging a "simple" migration because a specific native module—think bcrypt or certain database drivers—refused to compile. Node’s N-API (Node-API) is supposed to be portable, but Bun’s implementation of it is an ongoing work in progress. It’s getting better. Every release fixes bugs. But if you’re the one discovering those bugs at 2:00 AM on a Tuesday, the speed gains don't feel worth the gray hair.
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Memory Management and the Shadow of Zig
Bun is written in Zig, a low-level language that gives the developer manual control over memory. This is why Bun can outperform Node, which relies on the V8 engine’s garbage collector. V8 is a masterpiece of engineering, but it’s heavy. It’s hungry.
Bun uses the JavaScriptCore (JSC) engine—the same one that powers Safari. JSC generally starts up faster than V8. This makes Bun incredible for serverless functions where "cold starts" are the enemy. If you’re running AWS Lambda, Bun can save you real money.
However, JSC and V8 handle memory differently. Long-running processes in the Bun runtime have occasionally shown different heap profiles than what Node developers are used to. You can’t just copy-paste your existing max-old-space-size flags and expect everything to behave. You're essentially switching the entire brain of your application. That requires a level of re-testing that most companies simply don't have the budget or the patience for.
The Tooling Trap
One of Bun's biggest selling points is its all-in-one nature. It wants to replace your test runner (Jest/Vitest), your bundler (esbuild/Webpack), and your package manager (npm/yarn/pnpm).
Why this is actually a headache
Imagine your current CI/CD pipeline. It’s a delicate Rube Goldberg machine of GitHub Actions, Husky hooks, and Snyk vulnerability scans.
When you introduce Bun, you aren't just changing the runtime. You’re often pressured to change the whole workflow to get the "full benefit." Suddenly, your linting rules behave differently. Your test coverage reports need a new plugin because Bun’s built-in test runner outputs a different format.
And let’s talk about bun.lockb. Bun uses a binary lockfile. Why? Because it’s faster to read and write. But you can't easily read it in a git diff. If two developers change a dependency at the same time, resolving that conflict is a nightmare compared to the plain-text package-lock.json or pnpm-lock.yaml. Yes, you can export it to a human-readable format, but that’s just one more step in a process that was supposed to be "simpler."
Package Management Speed: A Double-Edged Sword
Bun’s package manager is fast. Kinda scary fast. It uses hardlinks and a global cache to make bun install feel instantaneous.
But speed can mask underlying issues. I’ve seen cases where Bun installs packages that have peer dependency conflicts that npm would have screamed about. Node’s ecosystem is built on a specific, often rigid, resolution logic. Bun tries to be smarter and faster, but sometimes "smart" leads to "unpredictable."
If your project relies on a complex mono-repo setup using Turborepo or Nx, switching to the Bun runtime for package management can break the way workspaces are linked. It’s not that Bun is "bad"—it’s just that the ecosystem was built for Node’s specific brand of chaos.
The Reality of Production Stability
Node.js is boring. That is its greatest strength.
Fortune 500 companies run on Node because they know exactly how it fails. They know the memory leak patterns. They know how it handles backpressure in streams. Bun is still in its "move fast and break things" phase. The development velocity is insane, which is exciting, but for a CTO, "insane velocity" is another word for "instability."
The "New Shiny" Tax
We’ve seen this before with Deno. Deno was supposed to kill Node too. It had security by default, first-class TypeScript support, and a prestigious pedigree (created by Ryan Dahl, the father of Node). But Deno struggled because it broke compatibility with the existing ecosystem.
Bun learned from Deno’s mistakes by prioritizing Node compatibility. Yet, the Bun runtime still feels like it's in beta for anything involving complex, legacy infrastructure.
If you’re running a high-traffic API where every millisecond of downtime costs five figures, are you really going to swap your stable Node v20 environment for a runtime that’s barely a few years old? Most won't. They’ll wait. They’ll let the startups and the hobbyists find the edge cases.
Debugging: The Final Frontier
Debugging in Node is a dream. Chrome DevTools, VS Code integration, heap snapshots—it’s all there.
Bun has made strides here, but it’s still playing catch-up. Using the bun --inspect flag works, but the integration isn't as seamless across all IDEs. When things go wrong in Bun, they often go wrong at the Zig/C++ level, and the error messages can be... cryptic.
If a Node process crashes, you usually get a stack trace that points to a line of JavaScript. In the early days of Bun, you’d occasionally just get a "Segmentation Fault." While those are becoming rarer, the "trust" factor isn't quite there yet.
Is the Bun Runtime Worth the Trouble?
So, should you actually use it?
Honestly, it depends on what you're willing to lose. If you are starting a new project today and you want the best possible developer experience, Bun is a strong contender. The speed of the test runner alone can save a developer hours of "waiting for CI" every week.
But if you’re looking at an existing, revenue-generating application, the Bun runtime is a massive risk. It’s a "pain" because it forces you to re-evaluate every single assumption you’ve made about your environment.
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Actionable Next Steps for the Skeptical Developer
If you’re tempted by the speed but terrified of the breakage, don’t do a full migration. That’s a recipe for disaster. Try these incremental steps instead:
- Use Bun for Scripts Only: Replace your messy bash or python utility scripts with TypeScript scripts run via
bun run. It’s a low-risk way to get used to the tool. - Test Runner First: Try running your existing Jest or Vitest suite using
bun test. If it passes, you’ve just sped up your development cycle without touching your production runtime. - The "Shadow" Build: Set up a secondary CI job that runs your app using Bun but doesn't deploy it. See how many tests fail. Monitor it over a month.
- Edge Functions: If you use Vercel or Netlify, experiment with Bun for small, isolated edge functions where cold start times are the primary bottleneck.
- Check Your Native Modules: Before even considering a move, audit your
package.jsonfor anything that usesnode-gyp. If you have lots of C++ addons, your migration path will be rocky.
The Bun runtime is an incredible feat of engineering. It has forced the Node.js team to finally take performance seriously again (we’re seeing huge speedups in Node 22 and 23 because of the competition). But don't let the hype-train convince you that it’s a free lunch. Every millisecond saved in execution time might cost you an hour in debugging a weird environment quirk. Proceed with caution, plenty of tests, and a very healthy dose of skepticism.
The tech world moves fast, but stable infrastructure is built on the bones of tools that have survived the test of time. Bun is still earning its scars. Give it time, or give it a small, isolated corner of your codebase to prove itself. Just don't bet the whole farm on it until you've felt the pain for yourself in a staging environment first.