Resolving import/no-unresolved Errors with TypeScript Declaration Files in ESLint

Learn how to fix `import/no-unresolved` errors in your TypeScript project while using ESLint in a Lerna monorepo setup.
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Resolving import/no-unresolved Errors with TypeScript Declaration Files in ESLint

Understanding the Issue

When ESLint throws an import/no-unresolved error, it indicates that it can't locate an imported module. This can occur for several reasons, but with TypeScript declaration files, the problem often lies in the ESLint settings and the way modules are resolved.

For instance, in your project, you might have the following import statement in your code:

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However, when ESLint checks this import, it fails to resolve the path, resulting in the import/no-unresolved error.

Step-by-Step Solution

The key to resolving this error is adjusting your ESLint configuration to better accommodate TypeScript files. Here’s how to do it:

1. Update the ESLint Configuration

Your current ESLint configuration looks impressive, but it's missing a crucial part that supports TypeScript imports. You need to add the plugin:import/typescript to your extends array. This line ensures ESLint can handle TypeScript correctly by using the appropriate plugins.

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2. Why This Works

By adding plugin:import/typescript, you enable ESLint's import plugin to correctly resolve TypeScript files. The original import/no-unresolved error appears because the ESLint import plugin is not configured to understand TypeScript's mode of module resolution, especially in a monorepo context.

TypeScript Support: The addition provides ESLint with the necessary rules to check TypeScript imports appropriately.

3. Additional Configuration (If Needed)

While the above adjustment should solve your issue with declaration file imports, it’s essential to ensure that your overall ESLint setup is optimized for a TypeScript environment. Here are a few pointers:

Prettier Integration: Ensure that prettier/@ typescript-eslint is included for formatting TypeScript, making your code more readable.

Webpack Resolver: If you're using Webpack, confirm your resolver settings accommodate .ts and .tsx extensions.

Conclusion

Errors like import/no-unresolved can be frustrating, but understanding how to configure ESLint correctly for TypeScript can save you significant time. By following the steps outlined here, you should be able to resolve your import errors without switching to less strictly defined rules.

With the added import/typescript plugin, your ESLint setup in a Lerna monorepo should now function smoothly, allowing you to develop confidently with TypeScript. Happy coding!