Jest default import is not working for 'express-session'

Problem

jest needsimport * as session from 'express-session'; but nestjs needs import session from 'express-session';

how to solve this? any tsconfig change or how to make jest know

Solution

To handle the import difference between Jest and Nest.js when it comes to the express-session module, you can use the moduleNameMapper option in Jest's configuration to map the import to the correct module.

In your Jest configuration (usually found in jest.config.js or jest.config.ts), you can add the moduleNameMapper like this:

module.exports = { 
    // ... other Jest configurations 
    ...  moduleNameMapper: {
        '^express-session$': 'express-session', // Map 'express-session' to itself  },
    };

If you are using TypeScript, you can do the same in the jest.config.ts file:

export default { 
// ... other Jest configurations 
...  moduleNameMapper: { 
'^express-session$': 'express-session', // Map 'express-session' to itself  
}, };

By adding this configuration, Jest will understand the import statement import * as session from 'express-session'; and properly map it to import session from 'express-session';.

Please note that the moduleNameMapper option allows you to specify regular expressions to match module names. In this case, we are using a simple mapping to map 'express-session' to itself, which should solve the issue you are facing. However, depending on your project's structure and other dependencies, you might need to adjust the moduleNameMapper to fit your specific use case.

Remember to keep an eye on your Jest configuration file for any other potential conflicts or adjustments needed. With this setup, Jest should be able to recognize the import * as session from 'express-session'; statement correctly in your tests.

If you need jest to understand ts

To make Jest read the import session from 'express-session'; expression correctly, you need to ensure that the TypeScript compiler options are set appropriately in your project.

In your tsconfig.json file, you can specify the "esModuleInterop" option to true. This option enables the compatibility with the CommonJS module format, making the import statement import session from 'express-session'; work as expected.

Here's how to do it:

{
  "compilerOptions": {
    "esModuleInterop": true,
    "module": "commonjs", // This might already be set correctly, but double-check it.
    // ... other compiler options ...
  },
  // ... other configurations ...
}

By setting "esModuleInterop": true, TypeScript will allow you to use default imports (import session from 'express-session';) for modules that use the CommonJS pattern, such as express-session.

After making this change to your tsconfig.json, try running your Jest tests again, and it should be able to recognize the import session from 'express-session'; statement without any issues.

Remember that you might need to clear any Jest cache by running npx jest --clearCache to ensure the new configuration takes effect.