Скачать или смотреть How to Make ts-jest Work with import/export Syntax in JavaScript Files

Discover how to configure `ts-jest` and `jest` for ES6 `import/export` syntax in your JavaScript files to avoid common errors and ensure seamless testing.
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Resolving ts-jest Import/Export Syntax Issues in Jest

Introduction

When working in modern JavaScript and TypeScript environments, utilizing ES6 import/export syntax has become the norm. However, if you've ever encountered the dreaded SyntaxError: Unexpected token 'export' while running tests with Jest on files that include import/export syntax, you're not alone. This issue typically arises when Jest is unable to correctly parse and handle these module formats, leading to frustrating roadblocks in your testing process. Fortunately, there are clear steps you can take to resolve this problem efficiently.

The Problem

The core of the issue lies in how Jest and ts-jest handle JavaScript and TypeScript files, especially when mixing .js and .ts files with ES modules. Let's consider a scenario where you have:

foo.js: a JavaScript file exporting a constant

bar.ts: a TypeScript file importing from foo.js and performing calculations

bar.test.ts: a TypeScript test file testing functionality from bar.ts

When you attempt to run your tests using npm run test, Jest will fail on importing the ES module from foo.js, as shown by the error message.

Step-by-Step Solution

Now, let’s walk through the necessary steps to configure ts-jest and jest properly to work alongside ES module syntax.

1. Update Your Dependencies

Ensure you're using compatible versions of Jest and ts-jest. It's recommended to have versions that are >= 27.0.0 for better ESM support:

[[See Video to Reveal this Text or Code Snippet]]

2. Update Your Configuration Files

a. tsconfig.json Configuration

You'll need to adjust your TypeScript configuration file to allow JavaScript files and enable interoperability between modules. A minimal setup would look like this:

[[See Video to Reveal this Text or Code Snippet]]

b. jest.config.ts Configuration

Next, you will set up the Jest configuration file (jest.config.ts) to properly handle ES modules. Here’s a template for your Jest configuration:

[[See Video to Reveal this Text or Code Snippet]]

3. Verify Your Project Structure

Make sure your project structure resembles the following for easy management and testing:

[[See Video to Reveal this Text or Code Snippet]]

4. Run Your Tests

Now you are ready to execute your tests. Simply use:

[[See Video to Reveal this Text or Code Snippet]]

If everything is set correctly, Jest should successfully run your tests without throwing errors related to import/export syntax.

Conclusion

By following these steps, you should be able to eliminate the common issues associated with using ES6 import/export syntax in Jest tests, even when dealing with both JavaScript and TypeScript files. Remember to keep your dependencies updated and configurations aligned with the latest best practices. Testing your code effectively ensures a smooth development experience and higher code quality. Happy coding!