Why I Replaced Node.js and npm With Bun Across All My Projects
Bun is a runtime, package manager, test runner, and bundler in one binary. After running it in production for months, here is an honest account of where it wins and where to watch out.
I switched every project I actively develop to Bun-runtime, package manager, test runner, and all. This was not a reaction to a viral benchmark. It was a series of small decisions that accumulated until Node.js was the outlier on my machine.
Here is what actually changed and what I learned.
The install speed is real
The first obvious thing is package installation. bun install on a project with a large lockfile runs in a second or two. The same project with npm install or pnpm install takes fifteen to thirty seconds depending on cache state.
This matters more than it sounds. It comes up in CI runs, in Docker builds, in onboarding someone new to a repo, and every time you switch branches and need to reconcile packages. Over a day of development it adds up to a meaningful amount of time not spent waiting.
The speed comes from Bun’s package manager being written in Zig, using system calls directly, and maintaining a global package cache that shares installed packages across projects rather than copying them each time.
TypeScript without the ceremony
Bun runs TypeScript natively. No ts-node, no tsx, no compile step for scripts.
bun scripts/generate-icons.tsThat works. The TypeScript is executed directly. For the prebuild scripts in my blog-font generation, icon generation-this means the scripts are just TypeScript files that run like shell scripts, with full type safety and IDE support, without a build step.
For application code, this also simplifies the development loop. The import-edit-run cycle has no compilation in the middle.
bun test
Bun ships a test runner compatible with Jest’s API. The same describe, it, expect, beforeEach structure works. Migration from Jest is usually mechanical.
The runner is fast because it runs in Bun and because it parallelizes by default. A test suite that took 8 seconds in Jest runs in under 2 in Bun.
There is no plugin ecosystem as deep as Jest’s, and some advanced matchers need workarounds. For most projects, what ships with Bun is sufficient.
The package manager interop story
Bun reads package.json exactly as npm does. It understands workspaces in the same format. It generates a bun.lockb lockfile instead of package-lock.json, but you can also use --frozen-lockfile in CI the same way.
The one behavioral difference worth knowing: Bun is stricter about peer dependency resolution by default. Projects that had quietly wrong peer dependencies under npm sometimes surface warnings or errors under Bun. Those are real problems-Bun just reports them instead of silently guessing.
Where Node.js still matters
Bun’s Node.js compatibility is very high but not complete. Most npm packages work without modification. Some packages that use Node-specific internals-certain native addons, some database drivers-have compatibility quirks.
If you are migrating an existing production system with a complex dependency tree, test compatibility before committing. For greenfield projects, I have not hit a wall.
The ecosystem tooling also still assumes Node in some places. Some CI templates, Dockerfile examples, and deployment guides show Node commands by default. Substituting bun is usually straightforward, but it is an extra step.
The practical result
Every project I own runs on Bun. Install times are fast enough that I stopped thinking about them. TypeScript scripts run without a build step. Tests run without waiting. The unified binary means one fewer category of “what version of this tool do I have installed.”
The migration is low-risk. Drop in Bun, update your scripts in package.json to use bun instead of node or npm, and run the test suite. Most of the time it works immediately.
The Bun docs are thorough. Start there if you want specifics on any of the APIs or compatibility notes.