Old Way - Common Js

// import
const express = require('express')

// export
module.export = express

New Way- Modules

// import
import express from 'express

// export
export default express

Modules is a fancier name for Files. It is that simple.

Common Js is the original way to package code in node js. Node js also supports the Ecma Script modules(import/ export syntax).

Package code meaning, putting larger code in different-different files and and accessing them as you need.

For example, you can divide controllers, models, routes and you views in different different files inside multiple folders and you can access them using two ways,

Common js(old)

Es modules(NEW)

Es modules is Ecma script standard modules as we use to package code in our frontend application and access them using import export syntax. This is cool, right?

Here is both way with example:

Common js -

file: sum.js
function sum(a,b) {
    return a + b

modules.export = calculate

file: calculator.js
const sum = require('sum')
function calculator() {
    const sumResult =  sum(23, 55)
    console.log(sumResult)

calculator()

Es Modules

file: sum.js
function sum(a,b) {
    return a + b

export default sum

file: calculator.js
import sum from './sum.js'  // Es Modules sum is in same directory
function calculator() {
    const sumResult =  sum(23, 55)
    console.log(sumResult)

calculator()

Keep in mind:

You can change Your code behavior using package.json type field

{
  "name": "backend",
  "version": "1.0.0",
  "description": "Backend of Online Examination System",
  "main": "index.js",
// you can use import and export syntax of Ecma script this way
  "type": "module", // module - Treated as Ecma Script modules Es Modules
  "scripts": {
    "start": "node -r dotenv/config index.js dotenv_config_path=backend.env",
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "dotenv": "^16.4.5",
    "express": "^4.19.2"
  }

// change type field to commonjs to change the behaviour to default,
// you can omit this too, this is default way
 "type": "commonjs", // commonJs - default modules of Node js

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