ES Modules vs CommonJS

Two Module Systems

	CommonJS (CJS)	ES Modules (ESM)
Syntax	`require()`, `module.exports`	`import`, `export`
Loading	synchronous	asynchronous, supports top-level `await`
Node.js default for `.js`	yes, unless `"type": "module"`	with `"type": "module"` or `.mjs`
Used by	older Node code, NestJS (compiled output)	browsers, Vite, Next.js, modern Node

How TypeScript Emits Imports

You write import/export in TypeScript either way. The module option decides the output. With "module": "commonjs":

import { readFileSync } from "node:fs";
export const VERSION = "1.0";

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.VERSION = void 0;
const node_fs_1 = require("node:fs");
exports.VERSION = "1.0";

With "module": "nodenext" TypeScript follows Node rules exactly: in an ESM package, relative imports must include the extension (import { x } from "./util.js", even though the file is util.ts).

Which Settings to Use

Project	`module` / `moduleResolution`
Node.js app or library	`nodenext` / `nodenext`
Next.js, Vite, any bundler	`esnext` / `bundler`
NestJS (default)	`commonjs` / `node`

Note: Details of these options are in the advanced level (tsconfig.json in Depth).