PocketJS

High-performance JSX UI outside the browser, with native rendering, standard Vue Vapor and Solid support, a Tailwind design system, and 60 FPS animation under an 8 MB memory budget. Write Solid or Vue Vapor components, run them on QuickJS, and let PocketJS move layout, styling, text and animation into a tiny no_std Rust core.

It runs on real PSP hardware, PPSSPP, PS Vita via Vita3K (real-hardware run pending), the browser (WASM), native macOS windows (wgpu) and headless Bun. Full design + contracts: DESIGN.md. PocketJS is growing into a family of specialized runtimes — Rust cores, spec-pinned surfaces, one QuickJS guest — documented in RUNTIMES.md; the 3D base lives in pocket3d/, and its first game runtime is OpenStrike.

Screenshots

pocketjs-hardware-demo.mp4

These PocketJS UIs run smoothly at 60 FPS on a Sony PSP within an 8 MB memory budget, including animated transitions and input feedback.

Gallery	Settings
Motion Lab — baked keyframe timelines	Motion Lab — 3D pipeline

Quickstart

bun install
bun pocket check --target psp         # schema + capabilities + ordinary app TypeScript
bun pocket compile --target psp       # check + emit JS/pak from the resolved plan
bun pocket build --target psp -- --release

# Low-level compiler commands used by framework demos/tests:
bun scripts/build.ts hero             # -> dist/hero.js + dist/hero.pak
bun scripts/build.ts hero-vue-vapor-main --framework=vue-vapor

Or drive everything through the pocket CLI: npm i -g @pocketjs/cli, then pocket doctor checks the bun / Rust / PSP toolchain (pocket setup installs what's missing), pocket create <name> scaffolds an app, and pocket dev|build|psp|hw|psplink wrap the scripts below.

The build is two-pass: pass 1 babel-transforms every module reachable from the entry (framework-specific JSX + TypeScript, content-hash cached in .cache/) while collecting class strings + text codepoints from the AST; then the Tailwind compiler writes styles.bin + src/styles.generated.ts, the font baker rasterizes Inter atlas slots for exactly the characters your app uses, and everything is packed into dist/<app>.pak. Pass 2 bundles with Bun (iife, unminified) from the cached transforms.

import { createSignal } from "solid-js";
import { Text, View } from "@pocketjs/framework/components";

export default function Counter() {
  const [count, setCount] = createSignal(0);

  return (
    <View class="flex-col items-center gap-4 p-4 bg-slate-50">
      <Text class="text-xl text-slate-950">Count: {count()}</Text>
      <View
        class="p-2 rounded-md bg-blue-600 focus:bg-blue-500 transition-colors duration-150"
        focusable
        onPress={() => setCount(count() + 1)}
      />
    </View>
  );
}

Mounting entries should look like ordinary app bootstrap code; the framework handles host detection, the generated style table, pak image uploads and the host frame callback:

import { mount } from "@pocketjs/framework";
import App from "./app.tsx";

mount(() => <App />);

Styling rules (compile-time, no runtime CSS): a class literal compiles iff every token is a supported utility (see DESIGN.md "Tailwind subset (v1)"); dynamic styling is ternaries of full literals, style={{...}}, or animate(). classList, hover: and template-interpolated classes are compile errors. rounded-full requires w-N h-N in the same literal.

Framework selection is explicit: set framework: "solid" or framework: "vue-vapor" in pocket.config.ts, or pass --framework=... to scripts/build.ts, scripts/dev.ts, or scripts/psp.ts. App state and component lifecycle come from the native framework package (solid-js or vue); PocketJS supplies host components, input, animation, assets and native runtime wiring.

@pocketjs/framework/components also exposes small app-shell primitives: Screen, Focusable, FocusScope, ActionHandler, FocusGrid, Portal, Modal, and ActionBar. FocusGrid gives a subtree explicit row/column d-pad traversal today; a virtualized grid can sit behind the same focus contract later. Portal mounts into the runtime overlay root, so modal/action-bar UI never participates in the active screen's flex layout. Modal owns a focus scope and blocks background button handlers while leaving frame animation lifecycle callbacks running; route switching is still ordinary app state, not a required router package.

Commands

bun play vita hero                    # build, install and launch in Vita3K
bun play vita gallery --fullscreen    # stretch to the host's full screen
bun play --help                       # list every runnable demo
bun run test                          # spec contract + tailwind parser tests
bun pocket check --target psp         # validate pocket.json + resolved target contract
bun pocket compile --target psp       # typecheck and compile, for custom native hosts
bun pocket build --target psp         # typecheck, compile, and package the target
bun scripts/build.ts <app> [--framework=solid|vue-vapor] [--extra-chars=…]
bun run psp / bun run vita / bun run dev / bun run wasm
bun run e2e:vita                     # Vita3K, native-density 960x544 golden E2E
bun psplink                           # interactive real PSP switcher over PSPLINK
bun run hw hero --trace              # real PSP via PSPLINK + host0 trace
bunx tsc --noEmit                     # typecheck (babel owns the JSX transform)

Manifest-driven builds resolve pocket.json once into a small ResolvedBuildPlan. The JS/font/pak compiler and native backend consume that same serialized plan; planHash is only its build-time checksum. At startup, the bundle checks the native host's target and HostOps ABI. The app entry and its reachable imports use the app's ordinary TypeScript configuration.

The selected target profile also resolves viewport.rasterDensity. Layout and DrawList coordinates stay in the app's logical viewport; the compiler bakes font coverage and SVGs at that density, prefers same-directory @2x PNG, sprite and raw-PAK siblings when present, and asks the core to bake its own masks at the same density. Dynamic texture producers read the identical value from platform.pixelRatio—they never branch on a target name:

import { platform } from "@pocketjs/framework/platform";

const canvas = makeTexture(logicalWidth * platform.pixelRatio);

Missing raster siblings deliberately fall back to the 1x source; malformed siblings fail the build if their dimensions do not preserve logical size.

Capabilities are plain framework API identifiers. requires must exist on the selected host; enhances resolves to booleans available from @pocketjs/framework/platform:

import { hasFeature } from "@pocketjs/framework/platform";

if (hasFeature("input.analog.left")) installAnalogNavigation();
else installButtonNavigation();

Literal hasFeature() calls are folded to booleans during a manifest build, so the unavailable branch is absent from the target bundle. platform.features remains available for computed queries and introspection. Capabilities describe fixed host API support, not permissions or live device state. Custom native hosts should use extractHostBuildInputs() and hostBuildEnvironment() from @pocketjs/framework/manifest; the complete Plan remains an internal build IR.

The complete design, including authority boundaries, compatibility rules, typed backend dispatch, target/ABI runtime checks, extension points, and current limitations, is documented in Platform contracts.

The Vita host is documented in native-vita/README.md. It preserves PocketJS's 480x272 logical layout while rasterizing geometry, fonts, vectors and core masks at Vita's native 960x544 density. Physical controls, analog input, and front-panel multi-touch snapshots are supported; PSP builds retain their controller-only fallback.

DevTools + time travel

Pocket DevTools (DEVTOOLS.md) is built into every bundle: a component tree with semantic names (debugName / <Named>), hover-to- highlight on the device screen (real PSP included, over the PSPLINK USB cable), pause/step, a REPL, console.log from hardware, and an always-on input-tape flight recorder — sessions replay byte-exactly because the whole runtime is fixed-dt deterministic.

bun run devtools                      # panel + hub + USB bridge, one process
bun run devtools cards                # + build, link and launch cards on a real PSP
bun run tape replay <app> <tape.json> --png 60   # render any frame headlessly
bun run tape:check                    # session-golden replay regression

On-demand device screenshots (📷 in the panel) work on every host — on real hardware the raw VRAM rides the usbhostfs mount and the bridge encodes the PNG desktop-side.

Determinism + the sim host

Time is a frame counter, not the wall clock (DETERMINISM.md): the virtual clock (@pocketjs/framework/clock) makes the simulation rate a host policy (?hz=2 on the web host runs the 2 FPS world on a real screen), the effect shell (@pocketjs/framework/effects) quantizes async results onto frame boundaries, and the headless sim host (host-sim/) replays scripted user journeys as byte-exact per-frame pixel traces — test/sim.test.ts is the proof, scripts/flake-lab.ts the wall-clock control experiment.

Fonts: Inter (OFL), vendored in assets/fonts/.