Solving the Infamous Metro Cannot Resolve FS Error in Nx Monorepo + React Native Projects

If you’re reading this, chances are you’ve stumbled upon the notorious “Metro Cannot resolve FS” error in your Nx monorepo + React Native project. Don’t worry, you’re not alone! In this comprehensive guide, we’ll delve into the root cause of this error, and provide you with clear, step-by-step instructions to resolve it once and for all.

What is the Metro Cannot Resolve FS Error?

The “Metro Cannot resolve FS” error typically occurs when Metro, the bundler used by React Native, is unable to locate the file system (FS) module. This error can manifest in various ways, such as:

• Error: Unable to resolve module `fs` fromMetro has encountered an error: Error: Unable to resolve module `fs`
• Error: Cannot resolve fs while processing metro-hermes-external
• Metro has encountered an error: Error: Cannot resolve module `fs`

Causes of the Metro Cannot Resolve FS Error

The root cause of this error can be attributed to one of the following reasons:

1. Incorrect Node.js version: Ensure you’re using a compatible Node.js version ( >= 14.17.0 ) with your React Native project.
2. Missing or outdated dependencies: Verify that your project’s dependencies, including Metro, are up-to-date and properly installed.
3. Nx monorepo configuration issues: Misconfigured Nx monorepo settings can lead to this error. We’ll explore this further in the solutions section.
4. File system permissions: Insufficient file system permissions can prevent Metro from accessing the FS module.

Solutions to the Metro Cannot Resolve FS Error

Now that we’ve identified the potential causes, let’s dive into the solutions:

Solution 1: Update Node.js and Dependencies

Ensure you’re running the latest version of Node.js ( >= 14.17.0 ) and update your project’s dependencies:

nvm install node
npm install --save-exact metro react-native

Solution 2: Configure Nx Monorepo Correctly

In your `nx.json` file, add the following configuration:

{
  "projects": {
    "my-app": {
      "root": "apps/my-app",
      "sourceRoot": "apps/my-app",
      "projectType": "application",
      "schematics": {},
      "prefix": "myapp"
    }
  },
  "cli": {
    "defaultCollection": "@nrwl/react-native"
  }
}

Make sure to update your `tsconfig.json` file to include the correct paths:

{
  "compilerOptions": {
    "outDir": "dist",
    "sourceMap": true,
    "noImplicitAny": true,
    "moduleResolution": "node",
    "esModuleInterop": true,
    "allowSyntheticDefaultImports": true,
    "jsx": "react-native",
    "lib": ["es2017"],
    "module": "commonjs",
    "resolveJsonModule": true,
    "isolatedModules": true,
    "paths": {
      "*": ["node_modules/*", "src/*"]
    }
  }
}

Solution 3: Update Metro Config

In your `metro.config.js` file, add the following configuration:

module.exports = {
  transformer: {
    getTransformOptions: async () => ({
      transform: {
        experimentalImportSupport: false,
        inlineRequires: false,
      },
    }),
  },
};

Solution 4: Fix File System Permissions

Run your React Native project with elevated permissions to ensure Metro can access the FS module:

sudo npx react-native start

Troubleshooting Tips and Tricks

If you’re still encountering issues, try the following:

• Delete the `node_modules` directory and run `npm install` again.
• Verify that your `jest.config.js` file is correctly configured.
• Check for any conflicts with other dependencies, such as ` react-native-fs`.
• Try cleaning the Metro cache by running `npx react-native start –reset-cache`.

Conclusion

In this comprehensive guide, we’ve explored the causes and solutions to the infamous “Metro Cannot resolve FS” error in Nx monorepo + React Native projects. By following the steps outlined above, you should be able to resolve this error and get your project up and running smoothly.

Remember to stay calm, and don’t hesitate to reach out to the community or online forums if you encounter any further issues.

Error Message	Solution
Error: Unable to resolve module `fs` from Metro has encountered an error: Error: Unable to resolve module `fs`	Update Node.js and dependencies, configure Nx monorepo correctly, and update Metro config.
Error: Cannot resolve fs while processing metro-hermes-external	Fix file system permissions, update Metro config, and troubleshoot tip: delete the `node_modules` directory and run `npm install` again.
Metro has encountered an error: Error: Cannot resolve module `fs`	Configure Nx monorepo correctly, update Metro config, and troubleshoot tip: try cleaning the Metro cache by running `npx react-native start –reset-cache`.

I hope this article has been helpful in resolving the “Metro Cannot resolve FS” error in your Nx monorepo + React Native project. Happy coding!

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