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DruidUI

DruidUI is a React-like framework that compiles to WebAssembly for building sandboxed user interfaces. Use it when you need to run untrusted UI code safely.

Why WebAssembly?​

Traditional approaches can't provide true sandboxing:

  • JavaScript - Can access all browser APIs
  • iframes - Limited state sharing, poor UX

WebAssembly provides complete isolation - code can only access explicitly granted functions.

Quick Start​

npx create-druid-ui my-app
cd my-app
npm install
npm run dev

Hello World​

import { createComponent, Context } from '@druid-ui/component';

let count = 0;

export const component = createComponent((ctx: Context) => {
  return (
    <main>
      <h1>Hello Druid!</h1>
      <button onClick={() => { count++; }}>
        Clicked {count} times
      </button>
    </main>
  );
});

Build & Deploy​

# Build to WASM
npm run build  # → dist/component.wasm

# Add to scroll
ui:
  - name: dashboard
    path: ui/dashboard.wasm
    route: /admin

Core Concepts​

Functional Components​

Similar to React and Mithril.js:

  • JSX/TSX syntax
  • Every event triggers full rerender (no complex diffing)
  • Module-level state (no hooks)
let items = ['todo 1', 'todo 2'];

export const component = createComponent(() => {
  return (
    <ul>
      {items.map(item => <li>{item}</li>)}
    </ul>
  );
});

Context​

Access route data via context:

export const component = createComponent((ctx: Context) => {
  return (
    <div>
      <p>Path: {ctx.path}</p>
      <p>User ID: {ctx.params.userId}</p>
    </div>
  );
});

Shadow DOM​

Each component renders in isolated Shadow DOM - styles can't leak in/out.

Development Workflow​

Raw Mode (Fast)​

Develop without WASM overhead:

<druid-ui no-sandbox src="/src/index.tsx"></druid-ui>
  • Instant hot reload
  • Normal browser debugging
  • Not sandboxed (dev only!)

Sandbox Mode (Production)​

Full WASM sandboxing:

npm run build
npm run preview
  • True isolation
  • Production-ready
  • Slower iteration

Extension System​

By default, WASM can only call d(), log(), and rerender(). Add custom APIs via extensions:

1. Define interface (WIT):

package my:api;

interface fetch {
  get-data: func(url: string) -> string;
}

2. Implement in host:

druidElement.extensionObject = {
  'my:api/fetch': {
    getData: async (url) => {
      const res = await fetch(url);
      return res.text();
    }
  }
};

3. Use in component:

import { getData } from 'my:api/fetch';

const data = await getData('/api/status');

See package documentation for full API reference.

Multi-Language Support​

Current: JavaScript/TypeScript ✅

Planned: Rust, C++ (waiting for WebAssembly Component Model maturity)

Limitations​

  • No async/await yet (use callback workaround)
  • Full rerenders on every event (less efficient than React)
  • JavaScript only for now
  • No SSR

Learn More​