Para
A JavaScript ecosystem in three pieces. Pick whichever ones you need; they don't depend on each other.
The three pieces
Para Lib
Cross-runtime npm packages: signals, parallel, pipeline,
arena, simd, csv, arrow, rtp,
mcp. Pure JS / Wasm, no platform bindings. Runs on Node, Bun, Deno, browsers, Cloudflare
Workers — anywhere V8 or JSC runs.
Distributed today as
parabun-browser-shims; individual @para/* packages on the roadmap. Module docs →
Para Lang
Optional .pts / .pjs syntax over the libs: pure /
memo functions, signal / effect / ~> /
-> reactive bindings, defer / arena blocks,
|> pipelines, ..! / ..& error operators, integer ranges.
Compiles to standard JavaScript that imports from Para Lib. The output runs anywhere — the language is
build-time only.
Compiler today is bundled inside the Para Runtime; standalone @para/transpile in development.
Language reference →
Para Runtime (ParaBun)
A fork of Bun that bundles Para Lib + Para Lang and adds native-only modules:
para:gpu (libcuda + Metal FFI), para:camera (V4L2), para:audio (ALSA
+ codecs + DSP), para:image (codecs + resize / blur / sharpen), para:gpio /
para:i2c / para:spi (Linux peripheral I/O), para:llm (Llama 3, Qwen2,
BERT, Whisper, OpenAI-compatible HTTP), and the higher-level composers (speech,
vision, assistant).
Native modules require ParaBun — there's no Node or browser equivalent for direct CUDA dispatch or kernel chardev access. parabun.script.dev →
Syntax (Para Lang)
Signals and effects
A signal declaration creates a reactive cell. Bare reads inside a tracked context (an
effect, a derived, a when block, or another signal's RHS) compile to
.get(). Bare writes compile to .set(). A signal whose initializer reads other signals
is auto-promoted to a derived value.
signal count = 0;
signal doubled = count * 2; // derived; recomputes when count changes
effect { console.log(doubled); } // runs once now, again on each change
count++; // count.set(count.get() + 1)Edge-triggered handlers
A when block fires its body once on each false→true transition of the predicate.
when not fires on the true→false transition. The predicate is tracked the same way an effect
body is.
signal score = 0;
when score >= 100 { unlockAchievement("century"); }
when not online { showOfflineBanner(); }Reactive bindings
A ~> B desugars to effect(() => { B = A; }), an assignment that stays in sync.
A -> fn desugars to effect(() => { fn(A); }), a call binding. Both are shorthand
for the common single-statement effect.
signal name = "world";
name ~> document.title; // title tracks name
name -> console.log; // logs on every changeRanges and pipelines
a..b is an exclusive integer range; a..=b is inclusive. The pipeline operator
|> threads a value through a sequence of unary calls.
for (const i of 0..n) work(i);
const evens = 0..=20 |> filter(i => i % 2 === 0);
const out = pixels |> map(p => p * 1.2) |> clamp(0, 255);Error operators
..! is .catch. ..& is .finally. They chain naturally
with await to flatten a try/catch block.
const data = await fetch(url).then(r => r.json())
..! err => defaults
..& () => spinner.hide();Compilation
Para files (.pts) are parsed by ParaBun's transpiler.
(Mainline Bun doesn't recognize the syntax — the parser additions are part of the ParaBun fork.) The output is
standard JavaScript with a handful of imports from para:* module specifiers.
On ParaBun, those specifiers resolve to built-in modules. On any other host (browser, Node, Bun, Deno,
Cloudflare Workers, …) alias them to parabun-browser-shims in your bundler.
// vite.config.ts
import { defineConfig } from "vite";
export default defineConfig({
resolve: {
alias: [{ find: /^para:(.*)$/, replacement: "parabun-browser-shims/$1" }],
},
});The same one-line alias works for esbuild, webpack, and rollup. See the install guide for the variants.
ParaBun is required for the build step today (it owns the .pts parser). A standalone
npm-installable transpiler (@para/transpile) is on the roadmap.
Examples
Three worked projects, one per host environment. Each is a complete project with file layout, source, and build commands.