How to Fix ‘A JavaScript Error Occurred in the Main Process’ in React

If you build a desktop application using Electron with a front-end created in React, you’ve probably encountered the dreaded alert:

“A JavaScript error occurred in the main process” That popup can feel like the universe flipped on you. The app won’t launch properly, or it launches then crashes, and you get no clear “this line of code broke” in your UI. What you’ll learn in this blog: why exactly this error appears in React/Electron projects, how you can diagnose it step-by-step, how to fix it with actionable code/config changes, and how to stop it from coming back. Also included: a comparison to existing blog posts (so you know this is more detailed), a handy table for quick lookup, and FAQs for your next “why is this still happening” moment.

What Does That Error Actually

The phrase “main process” refers to the Electron architecture: there’s a main process (Node­-style runtime, managing windows, app lifecycle, OS integration) and one or more renderer processes (your HTML/React UIs). When you see “A JavaScript error occurred in the main process”, it means something in that main process crashed or failed to initialize before the UI even got going (or while it was initializing). Common root issues: a module failed to require, a native addon .node file couldn’t load, paths got messed up after packaging, or your build config left out a dependency.

Uncaught Exception: Error: The specified module could not be found. \\?\C:\Users\username\AppData\Local\Temp\…\.tmp.node
That points directly to a native module (.node file) trying to load from a temp directory and failing. That kind of detail helps you zero in.

This Happens In a React + Electron Setup

When you build a React UI, you mostly worry about components, hooks, state. But when you wrap that UI in Electron to make it into a desktop app, now you introduce a main process. That main process may load native modules, manage file system access, pack assets, bundle your React build into app.asar, etc. The error often shows up because:

• Dev mode (npm start) uses unbundled files and works fine but after packaging things change (paths, architectures, asar bundling).
• A native module (for example a .node addon) gets bundled inside app.asar and Electron tries to load it from a temp folder but on some OSes or configs this fails.
• Your main.js entry has a missing require path or expects a file that isn’t included in the build output.
• You upgraded Electron or your builder but didn’t rebuild native modules or update config, so version mismatch strikes.
  So in short: the React part may be completely fine what breaks is the build/packaging or main process initialization.

How to Diagnose and Fix It

Capture the detailed error:

Don’t just dismiss the popup. Run your packaged app via command line so you see logs. Look for errors like Cannot find module 'xyz' or .node files referencing %Temp% or app.asar.unpacked. That gives you the clue which bucket you’re in.

Verify the main process code:

Open your main.js or electron-main.ts. Add debug log lines:

console.log('Main process starting');
console.log('Creating window…');

Check imports and file paths: win.loadFile(path.join(__dirname, 'index.html')) works after packaging? If you see win.loadURL('http://localhost:3000') in dev but packaging uses app.asar, you may need a branch:

const url = app.isPackaged
  ? `file://${path.join(process.resourcesPath, 'app', 'index.html')}`
  : 'http://localhost:3000';
win.loadURL(url);

Handle native module / asar issues:

If error mentions a .node file (native addon) inside app.asar.unpacked or %Temp%, you’re likely hitting the “native module cannot load from asar” scenario. Many devs solved it by adding in their build config:

"asarUnpack": ["**/*.node"]

or even disabling ASAR bundling ("asar": false) though that may increase size. Also rebuild native modules for the correct Electron version: npx electron-rebuild.

Align versions & rebuild dependencies:

If you upgraded Electron or your builder (like electron-builder) and didn’t rebuild native modules or change config, you may get version mismatch. In one StackOverflow answer: updating to the latest stable Electron fixed the error. So check package.json, ensure your electron, electron-builder, and any native addons are compatible. Delete node_modules and package-lock.json, then reinstall.

Check permissions, system dependencies, install state:

On Windows, sometimes Visual C++ redistributables or permissions cause the crash. If the .node file is denied or fails to load, you might need to ensure your installer runs as admin or that the user has correct rights. One user on Microsoft forums fixed it by uninstalling and reinstalling the app and cleaning app-data folders. Microsoft Q&A

Test on a clean machine/environment:

Before releasing, test your app on a VM or fresh machine. That ensures you catch missing dependencies, wrong architecture (x64 vs arm64), or packaging issues that don’t show up on your dev box. If it crashes there with the same main-process error, you know you’ve got a build/config issue.

Add crash-logging and error classification:

Use the define code at the top of this article in your project so you can capture main process errors more intelligently. For example in main.js:

import { classifyMainProcessError } from './shared/mainProcessError';
process.on('uncaughtException', (err) => {
  const errInfo = classifyMainProcessError(err);
  console.error('Main process crashed', errInfo);
  // optionally send to crash-reporting service
  app.exit(1);
});

Conclusion

If you’re dealing with How to Fix ‘A JavaScript Error Occurred in the Main Process’ in React, you’re not alone. The good news: this error can be diagnosed and fixed with a clear plan. Start by collecting the full error, trace through your main process code, check dependencies (especially native modules), verify packaging/bundler config, test in a clean environment, and instrument your app for future reliability.