Introduction#

OneJS lets you build UIs with React and TypeScript that render through Unity's GPU-accelerated graphics pipeline. Write familiar web code, deploy everywhere Unity runs.

Two Worlds, One Runtime#

OneJS bridges web development and game engines:

• Use React 19, hooks, JSX, and the npm ecosystem
• Render through Unity's UI Toolkit: GPU-accelerated, not a webview
• Access any C# API directly from JavaScript
• Deploy to desktop, mobile, web, and VR/AR from one codebase

For App Developers#

If you're building cross-platform applications, your current options have painful tradeoffs:

OneJS offers something different:

• True GPU rendering: UI Toolkit renders on the GPU, not a browser engine
• No webview overhead: No DOM, no layout engine, no Chromium
• React you already know: Hooks, components, JSX, TypeScript
• Unity's capabilities: Mix 2D UI with 3D scenes, use shaders, physics, audio
• Smaller builds: No bundled browser engine

For Game Developers#

Game UI development has been stuck in the past: verbose C# code, slow iteration, limited modding support.

OneJS brings modern practices to game UI:

• Declarative components: Write UI as React components, not imperative C# code
• Hot reload: See changes instantly without recompiling
• Separation of concerns: UI logic in JavaScript, game logic in C#
• First-class modding: Players can modify UI without touching game code
• Web dev accessibility: Expand your team with JavaScript developers

Platform Support#

From a single React codebase:

How It Works#

React Components → onejs-react Reconciler → UI Toolkit Elements → GPU Rendering

When you write:

<Button text="Click me" onClick={() => console.log("clicked")} />

OneJS creates a real UnityEngine.UIElements.Button and wires up the event handler. React's diffing algorithm ensures only changed properties update.

Developer Experience#

• TypeScript: Full type definitions for Unity APIs
• Hot Reload: Changes appear instantly during development
• CSS Modules: Scoped styles with .module.uss files
• Tailwind CSS: Utility-first styling, automatically escaped for USS
• npm Packages: Use libraries from the JavaScript ecosystem
• C# Interop: Call any Unity API with CS.UnityEngine.*
• AI-friendly: Point Cursor/Claude/ChatGPT at /llms-full.txt for full-docs context

Requirements#

• Unity 6.3 or later
• Node.js 18+ (for TypeScript compilation)

Next Steps#

• Quick Start: Get OneJS running and build your first UI
• Comparison: Deep dive into the value proposition