Node.js Error: "ReferenceError: require is not defined"

[Mercure28]

Why does "ReferenceError: require is not defined" appear in Node.js?

[TatyOko28]

This error happens when you use require() in an ES module (.mjs) instead of a CommonJS module (.cjs).

Solution 1: Use import instead of require (for ES Modules)

import express from "express";

Solution 2: Use CommonJS by renaming your file to .cjs
Or add this to package.json:

"type": "commonjs"