BunKit

Real AppKit apps for macOS, written in TypeScript on Bun.

Documentation

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bunkit builds mac apps out of real appkit windows, tables, menus and sheets, with all of the app logic in typescript. there's no webview anywhere, so the table in that screenshot is a real NSTableView.

import { Application, Window, VStack, HStack, Label, Button, TextField } from "bunkit";

const app = new Application({ name: "Hello" });

const name = new TextField({ placeholder: "Your name", grow: 1 });
const greeting = new Label({ text: "…" });

new Window({
  title: "Hello",
  size: { width: 360, height: 180 },
  content: new VStack({ spacing: 12, padding: 20 }, [
    new HStack({ spacing: 8 }, [
      name,
      new Button({ title: "Greet", primary: true, onClick: () => {
        greeting.text = `Hello, ${name.value}!`;
      }}),
    ]),
    greeting,
  ]),
}).quitOnClose();

await app.run();

try it

you'll need macos on apple silicon, bun 1.4 or newer, and the xcode command line tools (xcode-select --install).

git clone https://github.com/scarletindustries/bunkit
cd bunkit
bun install
./native/build.sh
bun run hello

bun run tour covers most of the api on one screen and bun run demo is the screenshot above. scene, rig, playground and particles are the metal examples. to turn one into an .app:

bun run bundle examples/demo.ts --name "My App" --id com.example.myapp --icon icon.png
open "dist/My App.app"

how it works

the objective-c runtime will hand you the full type signature of any method, so one bridge reads that and calls objc_msgSend through libffi instead of there being a wrapper per method. three layers sit on top of it:

src/ui/	layer 3	Window, VStack, Button, Table, 26 classes
src/objc.ts	layer 2	objc.NSWindow.alloc().init…(), marshalling, delegates, blocks
src/bridge.ts	layer 1	dlopen, packing arguments into buffers

every layer 3 object has a .native for when you need to drop to layer 2, which reaches all of appkit. the bridge and metal docs cover the rest.

3d

Scene3D is a view like any other, so it drops into a stack next to the labels and buttons.

const scene = new Scene3D({ grow: 1, camera: { position: [4, 2.6, 5] } });

scene.add(plane({ size: 40, color: "#20202a" }));
const cube = scene.add(box({ size: 1.1, position: [0, 0.55, 0], color: "#aa091b" }));

scene.onFrame(({ dt }) => { cube.rotation.y += dt; });

the annoying parts

appkit runs its own nested run loop for modal dialogs, menu tracking, live resize and drags, and js is frozen the whole time it's in there. so the dialogs are sheets that hand you a promise, and menu tracking and live resize pause the app until someone lets go of the mouse.

pointers are bigint, not number, so compare against 0n.

where it's at

it works and it's tested, but it only ad-hoc signs, there's no npm package yet, and swiftui hosting is missing.

bun test
bun run typecheck

contributing

run ./native/build.sh && bun run typecheck && bun test before you open a pr, and read CLAUDE.md for the conventions. for anything substantial, ask on discord (@hiett) first so we're not doing the same work twice.

bunkit is not affiliated with bun or with oven. it's named after the only runtime it runs on.

license

Apache License 2.0. see NOTICE for the attribution notices.