Node.js: 'SyntaxError: Cannot use import statement outside a module' (or the reverse, Error [ERR_REQUIRE_ESM]: require() of ES Module not supported). How do I fix ESM vs CommonJS mix-ups?

Cause: Node.js has two module systems. CommonJS uses require() and module.exports; ES modules (ESM) use import and export. Node decides which one a file is from its extension and the nearest package.json: .mjs is always ESM, .cjs is always CommonJS, and .js follows the "type" field ("module" means ESM; missing or "commonjs" means CommonJS). 'Cannot use import statement outside a module' means a file using import is being loaded as CommonJS. ERR_REQUIRE_ESM means CommonJS code called require() on a package that is ESM-only (many packages such as node-fetch 3, chalk 5 and nanoid 4 went ESM-only). Fix for 'Cannot use import statement outside a module': 1. If the project is meant to be ESM, add "type": "module" to package.json (or rename the file to .mjs). Then use import everywhere, include file extensions in relative imports ('./util.js'), and replace __dirname with import.meta.dirname (Node 20.11+) or fileURLToPath(import.meta.url). 2. If the project is CommonJS, change import x from 'y' to const x = require('y'). 3. In TypeScript, check the compiled output: "module" and "moduleResolution" in tsconfig.json (NodeNext is the usual choice for Node) must match the package type. For ts-node or Jest, use their ESM settings or a transform; tsx runs both styles. Fix for ERR_REQUIRE_ESM: 1. Upgrade Node: in Node 22.12+ and 20.19+, require() can load synchronous ES modules by default, which removes most of these errors. 2. Otherwise load it with a dynamic import inside CommonJS: const { default: fetch } = await import('node-fetch'); (inside an async function). 3. Or pin the last CommonJS major of that package, or move your project to ESM. Verify: node --version, check the nearest package.json "type" field and the file extension, then run the file again. Sources: https://nodejs.org/api/packages.html https://nodejs.org/api/esm.html https://nodejs.org/api/modules.html