Beyond the WebView: Engineering Truly Universal Desktop Apps with Expo and Tauri

For years, the dream of "write once, run everywhere" has been haunted by a single, bloated ghost: Electron. Don't get me wrong—Electron revolutionized the industry by lowering the barrier to entry for desktop apps. But as a senior engineer, I've grown tired of shipping 100MB 'Hello World' apps that consume 400MB of RAM just to idle.

Recently, I’ve been experimenting with a stack that feels like a genuine breakthrough for the universal app paradigm: Expo (React Native Web) paired with Tauri.

This isn't just about wrapping a website; it’s about leveraging the Expo ecosystem for mobile and web, while using Rust to handle the heavy lifting on the desktop. Here is how I’m engineering these truly universal applications.

The Architecture: Why this works

When we use Expo, we’re already writing code that targets iOS, Android, and Web. Expo's implementation of react-native-web is remarkably mature. However, the missing link has always been a performant desktop strategy.

By introducing Tauri into the mix, we replace Chromium with the system's native WebView (WebView2 on Windows, WebKit on macOS) and swap the Node.js backend for Rust.

The Comparison

Setting the Foundation

To make this work, your Expo project needs to be configured for the web first. I usually start by ensuring my app.json is optimized for web exports.

Once you have your Expo project running, you initialize Tauri in the root directory. The key shift here is pointing Tauri's devPath to your Expo development server (usually localhost:8081) and the distDir to your ./dist export.

// tauri.conf.json
{
  "build": {
    "beforeDevCommand": "npx expo start --web",
    "beforeBuildCommand": "npx expo export --platform web",
    "devPath": "http://localhost:8081",
    "distDir": "../dist"
  },
  "tauri": {
    "bundle": {
      "active": true,
      "targets": "all"
    },
    "allowlist": {
      "all": true
    }
  }
}

The "Universal" Bridge Pattern

The real engineering challenge is handling native modules. How do you call a Rust command on Desktop but a Native Module on iOS?

I’ve found success using an Adapter Pattern. I create an abstraction layer that detects the platform and routes the call accordingly. This keeps the UI components clean and agnostic of the underlying system.

// services/FileSystem.ts
import { Platform } from 'react-native';
import { invoke } from '@tauri-apps/api/tauri';

export const saveFile = async (data: string) => {
  if (Platform.OS === 'web') {
    if (window.__TAURI__) {
      // We are running in the Tauri desktop wrapper
      return await invoke('save_file_rust', { data });
    }
    // Standard browser download logic
    return downloadInBrowser(data);
  }
  
  // Mobile logic using expo-file-system
  return await ExpoFileSystem.writeAsStringAsync(...);
};

Performance Wins in Production

In a recent project where I migrated a data-heavy dashboard from Electron to this Expo-Tauri stack, the results were staggering.

1. Cold Start Time: Dropped from 4.2 seconds to 1.1 seconds.
2. Binary Size: Our installer went from 115MB (Electron) to 8MB (Tauri).
3. Efficiency: Idle RAM usage dropped by nearly 70%.

But the biggest win wasn't just performance; it was developer velocity. My team was able to use the same React components and business logic for the mobile app and the desktop app. We weren't maintaining two different codebases; we were maintaining one codebase with specific "hooks" for native desktop functionality via Rust.

The Rust Advantage

One breakthrough I had was moving high-compute tasks—like image processing and heavy JSON parsing—out of the JavaScript thread entirely. By writing these as Tauri commands in Rust, I utilized multi-threading that JavaScript simply can't match.

// src-tauri/src/main.rs
#[tauri::command]
fn process_data(data: String) -> String {
    // Rust logic here: highly performant and memory safe
    format!("Processed: {}", data)
}

fn main() {
  tauri::Builder::default()
    .invoke_handler(tauri::generate_handler![process_data])
    .run(tauri::generate_context!())
    .expect("error while running tauri application");
}

Final Thoughts

The era of bloated desktop apps is coming to a close. As senior engineers, we owe it to our users to ship software that respects their system resources. Combining Expo's universal UI capabilities with Tauri's lightweight Rust core is, in my experience, the most robust way to build cross-platform software today.

It requires learning a bit of Rust and thinking deeply about platform abstractions, but the result is a professional, native-feeling experience that truly goes beyond the WebView.