Bun - first impressions

After trying out Deno, the next thing on the list to look at is Bun. Key features:

  • Batteries included - like Deno
  • Drop-in replacement for node.js
  • Much faster then both node.js and Deno due to JavaScriptCore

So lets play!


  • Very easy - one curl-bash command
  • Docker image also available
  • Doesnt seem to be any OS level package (deb, rpm, etc) yet


Quickstart instructions work perfectly, bun init created a very minimal set of files:

├── bun.lockb
├── .gitignore
├── index.test.ts
├── index.ts
├── node_modules
├── package.json
└── tsconfig.json

Unit testing

bun test works out of the box if you create a .test.ts file and is very quick


biome seems to be the way to cleanup code on bun. Its quick and easy to setup:

bun add -d @biomejs/biome
bun x  @biomejs/biome check --apply .

Native code (node-gyp)

Seems to work! I was able to install the Confluent Kafka library, although I didnt try using it:

bun add @confluentinc/kafka-javascript
bun pm trust @confluentinc/kafka-javascript

Node project migration

So far bun is ticking all the right boxes so lets try migrating a node.js project to bun in a git branch.


Cleanup node remnants:

# eg:
rm .eslintrc.cjs package-lock.json tsconfig.* vitest* node_modules

Convert to bun project:

bun init

Cleanup stray bun settings (this project is part of a monorepo):

rm .gitignore

Reinstall all dependencies from package.json - Could have probably re-used the existing node_modules directory but wanted to prove can still resolve modules:

bun install

Thats it!

Re-run tests

This project has a bunch of vitest tests - most of them passed but there were some errors running integration tests, probably because of using node to run commands on the host. I can work with this :)

bun test

Result: Mostly working

Run the project

Moment of truth:

# eg
bun run src/app.ts

Result: Works first time!!! This is a resonably complex app that interfaces remote APIs through a node library and other binary network services. My face: 😳

Docker packaging

  1. Change FROM to reference a Bun tag
  2. Change the RUN node ... to RUN bun ...
  3. Make sure to run .ts files directly - there is no compiled JavaScript to deal with
  4. Thats it!

Result: Mostly working. I need to upgrade my shared dependency to also use bun and then enable it for linking with bun link, hopefully this resolves #5045


Highly promising technology with similar enjoyment level to Deno. Im converting the rest of my project to use Bun!

Post comment