The error "A module failed to load due to an error and AppRegistry.registerComponent wasn't called, JS engine: Hermes" typically occurs in React Native applications when there's an issue with loading a module, and the AppRegistry.registerComponent method is not called.

Error: Module failed to load - `AppRegistry.registerComponent` not called

If you encounter the error "A module failed to load due to an error and `AppRegistry.registerComponent` wasn't called, JS engine: Hermes" in your React Native application, it indicates a problem with module loading and component registration. Here's how you can resolve it:

  1. Check the Error Details: Examine the error message and stack trace to identify the specific module or component that is failing to load. Look for any additional error details that can provide insights into the issue.
  1. Verify Component Registration: Ensure that the main component of your application is properly registered using `AppRegistry.registerComponent` in your entry file (usually `index.js` or `App.js`). This is where your app's root component is registered.
// Example index.js or App.js
import { AppRegistry } from 'react-native';
import App from './App'; // Adjust the import based on your file structure
import { name as appName } from './app.json';

AppRegistry.registerComponent(appName, () => App);
  1. Check Module Dependencies: Verify that all the required dependencies for your modules are correctly installed. Run `npm install` or `yarn install` to make sure all dependencies are up-to-date.
  1. Inspect Native Modules: If your application uses native modules, ensure that they are properly linked. Run `react-native link` to link any newly added native modules or libraries.
  1. Update React Native: Ensure that you are using the latest version of React Native. Upgrade your project to the latest stable version by running:
# For npm
npm install react-native@latest

# For yarn
yarn add react-native@latest

After making these adjustments, restart your React Native development server and rebuild your application. The error should be resolved, and your app should load successfully.

If you encounter the error message:

Invariant Violation: "RestApp" has not been registered. This can happen if:

  • Metro (the local dev server) is run from the wrong folder. Check if Metro is running, stop it, and restart it in the current project.
  • A module failed to load due to an error and AppRegistry.registerComponent wasn't called.
  • Your index file is using the appName from the app.json name field to register your component, which in your case is "name": "restapphhopp".

To resolve this issue, update the moduleName in the ios AppDelegate.m file to "restapphhopp":


Double-check that the name specified in your app.json file matches the name used in your strings.jsx file.

Navigate to the android directory and run ./gradlew clean. Then, return to the parent directory and execute npx react-native run-android.

If you encountered the same issue while installing "react-native-circular-progress-indicator," you can try the following command:

npm start -- --reset-cache

The issue was resolved by performing the following steps:

  1. Navigate to the android directory.
  2. Execute ./gradlew clean.
  3. Return to the parent directory.
  4. Run npx react-native run-android.