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, consoles, and VR/AR from one codebase

For App Developers

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

• 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.*

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