$ node -v
v18.12.1
$ npm -v
8.19.2

$ npx create-next-app

✔ What is your project named? … esm
✔ Would you like to use TypeScript with this project? … No / Yes
✔ Would you like to use ESLint with this project? … No / Yes

cat package.json

{
  "name": "esm",
  "version": "0.1.0",
  "private": true,
  "scripts": {
    "dev": "next dev",
    "build": "next build",
    "start": "next start",
    "lint": "next lint"
  },
  "dependencies": {
    "@types/node": "18.11.11",
    "@types/react": "18.0.26",
    "@types/react-dom": "18.0.9",
    "eslint": "8.29.0",
    "eslint-config-next": "13.0.6",
    "next": "13.0.6",
    "react": "18.2.0",
    "react-dom": "18.2.0",
    "typescript": "4.9.3"
  }
}

{
  "name": "esm",
  "version": "0.1.0",
  "private": true,
  "scripts": {
    "dev": "next dev",
    "build": "next build",
    "start": "next start",
    "lint": "next lint"
  },
  "dependencies": {
    "@types/node": "18.11.11",
    "@types/react": "18.0.26",
    "@types/react-dom": "18.0.9",
    "eslint": "8.29.0",
    "eslint-config-next": "13.0.6",
    "next": "13.0.6",
    "react": "18.2.0",
    "react-dom": "18.2.0",
    "typescript": "4.9.3"
  },
  "type": "module"
}

npm run build

> esm@0.1.0 build
> next build

error - Failed to load next.config.js, see more info here https://nextjs.org/docs/messages/next-config-error

> Build error occurred
ReferenceError: module is not defined in ES module scope
This file is being treated as an ES module because it has a '.js' file extension and '/Users/okunokentaro/Desktop/esm-next-js/esm/package.json' contains "type": "module". To treat it as a CommonJS script, rename it to use the '.cjs' file extension.

/** @type {import('next').NextConfig} */
const nextConfig = {
  reactStrictMode: true,
  swcMinify: true,
}

module.exports = nextConfig

const someVariable = "hello";
module.exports = someVariable;

const a = require("./a");
console.log(`b.js: a is "${a}"`);

$ node b.js
b.js: a is "hello"

const someVariable = "hello";
export default someVariable;

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
const someVariable = "hello";
exports.default = someVariable;

$ node b.js
b.js: a is "[object Object]"

const a = require("./a");
console.log(a); // { default: 'hello' }
console.log(`b.js: a is "${a}"`);

const someVariable = "hello";
export = someVariable;

"use strict";
const someVariable = "hello";
module.exports = someVariable;

export const someVariable = "hello";

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.someVariable = void 0;
exports.someVariable = "hello";

export const someVariable = "hello";

export const someVariable = "hello";

const someVariable = "hello";
export default someVariable;

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
const someVariable = "hello";
exports.default = someVariable;

const someVariable = "hello";
export default someVariable;

const someVariable = "hello";
export default someVariable;

const someVariable = "hello";
export = someVariable;

"use strict";
const someVariable = "hello";
module.exports = someVariable;

Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead. (1203)

Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead. (1203)

a.js:2
export = someVariable;
^^^^^^

SyntaxError: Unexpected token 'export'
    at Object.compileFunction (node:vm:360:18)
    at wrapSafe (node:internal/modules/cjs/loader:1088:15)
    at Module._compile (node:internal/modules/cjs/loader:1123:27)
    at Module._extensions..js (node:internal/modules/cjs/loader:1213:10)
    at Module.load (node:internal/modules/cjs/loader:1037:32)
    at Module._load (node:internal/modules/cjs/loader:878:12)
    at Module.require (node:internal/modules/cjs/loader:1061:19)
    at require (node:internal/modules/cjs/helpers:103:18)
    at Object.<anonymous> (/Users/okunokentaro/Desktop/esm-next-js/b.js:1:11)
    at Module._compile (node:internal/modules/cjs/loader:1159:14)

/** @type {import('next').NextConfig} */
const nextConfig = {
  reactStrictMode: true,
  swcMinify: true,
}

module.exports = nextConfig

/**
 * @type {import('next').NextConfig}
 */
const nextConfig = {
  /* config options here */
}

export default nextConfig

$ npx create-next-app -V
13.0.6

$ npx create-next-app -h
Usage: create-next-app <project-directory> [options]

Options:
  -V, --version                      output the version number
  --ts, --typescript

    Initialize as a TypeScript project. (default)

  --js, --javascript

    Initialize as a JavaScript project.

  --eslint

    Initialize with eslint config.

  --experimental-app

    Initialize as a `app/` directory project.

  --use-npm

    Explicitly tell the CLI to bootstrap the app using npm

  --use-pnpm

    Explicitly tell the CLI to bootstrap the app using pnpm

  -e, --example [name]|[github-url]

    An example to bootstrap the app with. You can use an example name
    from the official Next.js repo or a GitHub URL. The URL can use
    any branch and/or subdirectory

  --example-path <path-to-example>

    In a rare case, your GitHub URL might contain a branch name with
    a slash (e.g. bug/fix-1) and the path to the example (e.g. foo/bar).
    In this case, you must specify the path to the example separately:
    --example-path foo/bar

  -h, --help                         output usage information

$ npm run build

> esm@0.1.0 build
> next build

warn  - Detected next.config.js, no exported configuration found. https://nextjs.org/docs/messages/empty-configuration
info  - Linting and checking validity of types
info  - Creating an optimized production build
info  - Compiled successfully
info  - Collecting page data
info  - Generating static pages (3/3)
info  - Finalizing page optimization

Route (pages)                              Size     First Load JS
┌ ○ /                                      4.33 kB        77.5 kB
├   └ css/ae0e3e027412e072.css             707 B
├   /_app                                  0 B            73.2 kB
├ ○ /404                                   181 B          73.3 kB
└ λ /api/hello                             0 B            73.2 kB
+ First Load JS shared by all              73.4 kB
  ├ chunks/framework-8c5acb0054140387.js   45.4 kB
  ├ chunks/main-11be7a5831576890.js        26.7 kB
  ├ chunks/pages/_app-3893aca8cac41098.js  296 B
  ├ chunks/webpack-8fa1640cc84ba8fe.js     750 B
  └ css/ab44ce7add5c3d11.css               247 B

λ  (Server)  server-side renders at runtime (uses getInitialProps or getServerSideProps)
○  (Static)  automatically rendered as static HTML (uses no initial props)

/**
 * @type {import('next').NextConfig}
 */
const nextConfig = {
    /* config options here */
}

export default nextConfig

/**
 * @type {import('next').NextConfig}
 */
const nextConfig = {
    env: {
        customKey: 'my-value',
    },
}

export default nextConfig

$ npm run build

> esm@0.1.0 build
> next build

info  - Linting and checking validity of types
info  - Creating an optimized production build
info  - Compiled successfully
info  - Collecting page data
info  - Generating static pages (3/3)
info  - Finalizing page optimization

Route (pages)                              Size     First Load JS
┌ ○ /                                      4.33 kB        77.5 kB
├   └ css/ae0e3e027412e072.css             707 B
├   /_app                                  0 B            73.2 kB
├ ○ /404                                   181 B          73.3 kB
└ λ /api/hello                             0 B            73.2 kB
+ First Load JS shared by all              73.4 kB
  ├ chunks/framework-8c5acb0054140387.js   45.4 kB
  ├ chunks/main-11be7a5831576890.js        26.7 kB
  ├ chunks/pages/_app-3893aca8cac41098.js  296 B
  ├ chunks/webpack-8fa1640cc84ba8fe.js     750 B
  └ css/ab44ce7add5c3d11.css               247 B

λ  (Server)  server-side renders at runtime (uses getInitialProps or getServerSideProps)
○  (Static)  automatically rendered as static HTML (uses no initial props)

{"type": "commonjs"}