Why @testing-library/jest-dom requires ts extensions for import itself?

If you are using TypeScript and have come across the @testing-library/jest-dom library, you may have noticed that it requires ts extensions for import itself. In this blog post, we will explore why this is the case and provide solutions to this problem.

Understanding the Issue

The @testing-library/jest-dom library is a popular testing utility for JavaScript applications. It provides a set of custom jest matchers that allow you to write more readable and maintainable tests. However, when using this library with TypeScript, you may encounter an issue where the library itself requires ts extensions for import.

This issue arises because the @testing-library/jest-dom package is written in TypeScript and includes type definitions. When importing the library, TypeScript expects the imported module to have a .ts or .tsx extension. However, the library’s entry point does not have a .ts extension, which leads to a TypeScript compilation error.

Solution 1: Using Declaration Merging

One solution to this problem is to use declaration merging in your TypeScript project. Declaration merging allows you to extend the type definitions of an existing module and provide additional typings.

To resolve the import issue with @testing-library/jest-dom, you can create a declaration file with the same name as the library’s entry point but with a .d.ts extension. In this file, you can merge the module declaration with an additional declaration that includes the .ts extension.

Here’s an example of how you can create the declaration file:

// jest-dom.d.ts

declare module '@testing-library/jest-dom' {
  import '@testing-library/jest-dom/ts-expect';
}

With this declaration file in place, TypeScript will recognize the import without any compilation errors.

Solution 2: Using a Custom Import

If you prefer not to use declaration merging, another solution is to create a custom import statement that includes the .ts extension. This can be achieved by creating a separate file where you import the library and export it with a different name.

Here’s an example of how you can create a custom import file:

// jest-dom-import.ts

import '@testing-library/jest-dom/ts-expect';

export const jestDom = jest;

In your TypeScript files, you can then import the library using the custom import:

import { jestDom } from './jest-dom-import';

This approach allows you to import the library without any TypeScript compilation errors.

Conclusion

The @testing-library/jest-dom library requires ts extensions for import itself when used with TypeScript. This is because the library is written in TypeScript and includes type definitions. However, you can overcome this issue by using declaration merging or creating a custom import statement.

By following the solutions provided in this blog post, you should be able to import @testing-library/jest-dom without any TypeScript compilation errors and continue writing tests with ease.

Why @testing-library/jest-dom requires ts extensions for import itself?