jasno

A TypeScript-first framework for single-page apps. Plain TypeScript: no JSX, no template language, no build configuration. Views are function calls (h.div(...)) that TypeScript type-checks like any other code. In development, each .ts file is served as a module with its types removed; jasno build bundles the application for production.

Quick start

npm create @jasno my-app
cd my-app
npm install
npm run dev

Example

import { component, h, mount, signal } from '@jasno/core';

const Counter = component(function Counter(): Node {
  const count = signal(0);
  return h.button(
    { type: 'button', onclick: () => count.update((n) => n + 1) },
    'Clicked ', count, ' times',
  );
});

mount(Counter, document.getElementById('app'));

The component body runs once. Passing count (or any function) as a child keeps the text live: jasno calls it again when count changes and updates the text node. Passing count() instead renders only the initial value.

Mistakes that would fail silently in other frameworks are type errors or diagnostics with a fix in the message.

What you get

• No build configuration. jasno dev strips types as it serves, one module per file. jasno build bundles with Rolldown into hashed chunks, one per lazy view, with source maps, integrity, the CSP, _headers and _redirects. npm packages are imported by name. A stylesheet in assets/ that imports tailwindcss is compiled by the project's @tailwindcss/cli.
• Checks. jasno check runs tsc on the browser and test programs plus jasno's own rules. In development, problems are reported with a code; npm run explain CODE prints the repair guide.
• Accessibility built in. The router moves focus to each view's heading; lost focus, unnamed controls and a few other mistakes are reported.
• Testing. @jasno/core/testing mounts components under node:test with happy-dom; the template adds Playwright in Chromium, Firefox and WebKit.
• Small. The production runtime with the router is about 16 KB gzipped.

Commands

Command	What it does
npm run check	Type-checks the application and tests, and runs jasno's rules
npm test	Runs component tests with node:test and happy-dom
npm run dev	Starts the development server
npm run build	Bundles the application for production into dist/
npm run preview	Serves dist/ as a static host would
npm run explain CODE	Prints the repair guide for a diagnostic code

Documentation

The package includes its documentation:

• AGENTS.md: the guide for coding agents. The AGENTS.md of a project made by npm create @jasno points to it.
• dist/jasno.d.ts: the full API, with a RECIPES block of common patterns.

The design and its decisions are in design/ in the repository.

Requirements

• Node >=24.12.0
• TypeScript ~7.0.2
• Browsers: Chrome and Edge 136+, Firefox 138+, Safari 18.4+

Repository

• jasno/: the runtime, the CLI and their tests (npm test, npm run check, npm run test:browser, npm run test:package, npm run test:template)
• create-jasno/: the npm create @jasno template (the @jasno/create package)
• design/: the specification, the agent guide and the public types