How to get vitest working with require of ES module

ONLINECAST

2 min read

·

05-10-2024

10

0

Share

Conquering the "require" Hurdle: Using Vitest with ES Modules

Vitest, a blazingly fast testing framework built for the modern JavaScript developer, thrives on the power of ES Modules. However, you might encounter a snag when your project uses require, the common module system of Node.js. This article breaks down why this conflict occurs and guides you through the solutions to ensure seamless testing with Vitest.

The Problem:

Vitest's core strength lies in its ES Module support. This means it expects your code to be organized using import and export statements, the way modern JavaScript does. require, while ubiquitous in Node.js environments, is not directly compatible with Vitest's ES Module system.

Scenario: Imagine you're working on a project where a legacy library is still using require. You've decided to embrace Vitest for your tests, but now you're facing a conflict between these two module systems.

Original Code (Example):

// myModule.js (using require)
const utils = require('./utils');

// your test file (using import)
import { test, expect } from 'vitest';

// your test (will fail)
test('myModule should work', () => {
  expect(utils.doSomething()).toBe('expected result'); 
});

Understanding the Conflict:

• ES Modules: Vitest relies on the browser's ES Module loader, which follows the import/export syntax for resolving dependencies.
• CommonJS Modules: require works with Node.js's CommonJS module system, which doesn't use import or export.

When you try to import a module that uses require, you're essentially mixing these two systems, resulting in an error.

Solutions:

1. Migrate to ES Modules:

   • Ideal Approach: The most effective solution is to gradually migrate the legacy code using require to ES Modules. This might involve some refactoring, but it ensures long-term compatibility and aligns your project with best practices.

2. Use Node.js Environment:

   • Workaround: If migrating is not immediately feasible, you can leverage Vitest's environment option.

   • Example:

     // vitest.config.js
     import { defineConfig } from 'vitest';
     
     export default defineConfig({
       environment: 'node', // Use Node.js environment 
     });
     

     This instructs Vitest to run your tests in a Node.js environment where require will work correctly. However, keep in mind that this approach may not guarantee full compatibility with Vitest's features.

3. "require" Wrapper:

   • Temporary Fix: If you have a specific module that you can't change, you can wrap its require statement in a function:

     // myModule.js
     function importModule(modulePath) {
       return require(modulePath);
     }
     const utils = importModule('./utils');
     

     Then import this function in your test file:

     import { importModule } from './myModule'; 
     const utils = importModule('./utils');
     

     This allows you to use require within a function that is imported by Vitest, effectively bridging the gap between the two module systems.

Key Points:

• Performance: Migrate to ES Modules to enjoy Vitest's full performance benefits.
• Long-Term Stability: ES Modules is the future of JavaScript module management, making a migration a worthwhile investment.
• Compatibility: While the environment and "require" wrapper offer temporary workarounds, they might not guarantee seamless functionality with all Vitest features.

Conclusion:

Understanding the interplay between Vitest's ES Module system and the require syntax allows you to choose the right approach for your project. Aim for a gradual migration to ES Modules for a stable and performant testing experience. By navigating this common challenge, you unlock the full potential of Vitest for your testing needs.

Resources:

• Vitest Documentation: https://vitest.dev/
• ES Modules: A Comprehensive Guide: https://javascript.info/modules
• CommonJS Modules: Node.js Documentation: https://nodejs.org/api/modules.html