It's been a busy couple weeks.
Important: the bun-cli
npm package is deprecated. It will not receive updates.
Please upgrade Bun by running:
# Remove the npm version of bun
npm uninstall -g bun-cli
# Install the new version
curl https://bun.sh/install | bash
For future upgrades:
bun upgrade
Now the fun part.
bun run
~35x faster package.json "scripts"
runner, powered by Bun. Instead of npm run
, try bun run
.
Like npm run
, bun run
reads "scripts"
in your package.json and runs the script in a shell with the same PATH
changes as npm clients. Unlike npm clients, it's fast.
You can use bun run
in projects that aren't using Bun for transpiling or bundling. It only needs a package.json
file.
When scripts launch a Node.js process, bun run
still beats npm run
by 2x:
Why? Because npm clients launch an extra instance of Node.js. With npm run
, you wait for Node.js to boot twice. With bun run
, you wait once.
For maximum performance, if nested "scripts"
run other npm tasks, bun run
automatically runs the task with Bun instead. This means adding many tasks won't slow you down as much.
bun run
supports lifecycle hooks you expect like pre
and post
and works when the package.json
file is in a parent directory.
Two extra things:
bun run
also adds anynode_modules/.bin
executables to the PATH, so e.g. if you're using Relay, you can dobun run relay-compiler
and it will run the version ofrelay-compiler
for the specific project.bun run
has builtin support for.env
. It reads:.env.local
, then.env.development
||.env.production
(respecting yourNODE_ENV
), and.env
in the current directory or enclosing package.json's directory
Oh and you can drop the run
:
Reliability
Lots of work went into improving the reliability of Bun over the last couple weeks.
Here's what I did:
- Rewrote Bun's filesystem router for determinism and to support catch-all + optional-catch-all routes. This is an oversimplification, but the routes are sorted now
- Improved testing coverage. Bun now has integration tests that check a simple Next.js app bundles & server-side prerenders successfully. If JavaScriptCore's JIT is not enabled while server-side rendering, the tests fail. Another integration test checks that a simple Create React App loads. It uses
bun create
to bootstrap the projects. - Fix all known unicode encoding & decoding bugs. Part of what makes parsing & printing JavaScript complicated is that JavaScript officially uses UTF-16 for strings, but the rest of the files on your computer likely use UTF-8. This gets extra complicated with server-side rendering because JavaScriptCore expects either a UTF-16 string for source code or a UTF-8 string. UTF-16 strings use about twice as much memory as UTF-8 strings. Instead of wasting memory, Bun escapes the strings where necessary (but only for server-side rendering)
- Fixed several edgecases with the
.env
loader..env
values are now parsed as strings instead of something JSON-like
There's still a lot of work ahead, but Bun is getting better.
Sometimes, speed and reliability is a tradeoff. This time, it's not. Bun seems to be about 3% faster overall compared to the last version (v0.0.36). Why? Mostly due to many small changes to the lexer. Inlining iterators is good.