vitest complains that “require is not defined” but I don’t use require

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Summary

The issue at hand is that vitest is throwing a ReferenceError complaining that require is not defined in an ES module scope, even though the test file does not explicitly use require. This error is confusing because the test file is written using ES module syntax and the package.json file does not have a type: module entry.

Root Cause

The root cause of this issue can be attributed to several factors:

  • Incompatible dependencies: Some dependencies might be using CommonJS syntax, which relies on require for imports.
  • Transpilation issues: The code might be transpiled incorrectly, leading to require being used in the transpiled code.
  • vitest configuration: The vitest configuration might be set up to use CommonJS instead of ES modules.

Why This Happens in Real Systems

This issue can occur in real systems due to:

  • Mixed module systems: Using both ES modules and CommonJS in the same project can lead to conflicts.
  • Dependency inconsistencies: Dependencies might be using different module systems, causing issues when trying to import them.
  • Incorrect configuration: Misconfigured build or test tools can lead to incorrect transpilation or module resolution.

Real-World Impact

The real-world impact of this issue includes:

  • Failed tests: Tests will fail due to the ReferenceError, making it difficult to ensure the correctness of the code.
  • Development delays: Resolving this issue can be time-consuming, delaying the development process.
  • Frustration: The confusing error message can lead to frustration among developers, especially those new to vitest or ES modules.

Example or Code (if necessary and relevant)

import fs from "node:fs";
import { test, expect } from "vitest";

test("Creating store", () => {
  expect(fs.existsSync("my-file.dat")).toBe(true);
});

How Senior Engineers Fix It

Senior engineers can fix this issue by:

  • Checking dependencies: Verifying that all dependencies are using the correct module system.
  • Configuring vitest: Ensuring that vitest is configured to use ES modules.
  • Transpilation: Checking the transpilation process to ensure that require is not being used incorrectly.

Why Juniors Miss It

Junior engineers might miss this issue due to:

  • Lack of experience: Limited experience with ES modules and CommonJS can make it difficult to identify the root cause.
  • Insufficient knowledge: Not being familiar with the vitest configuration options or the implications of mixed module systems.
  • Overlooking details: Failing to notice the subtle differences between ES module and CommonJS syntax.