Node has a built-in module system.

A Node.js file can import functionality exposed by other Node.js files.

When you want to import something you use

const library = require('./library')

to import the functionality exposed in the library.js file that resides in the current file folder.

In this file, functionality must be exposed before it can be imported by other files.

Any other object or variable defined in the file by default is private and not exposed to the outer world.

This is what the module.exports API offered by the module system allows us to do.

When you assign an object or a function as a new exports property, that is the thing that’s being exposed, and as such, it can be imported in other parts of your app, or in other apps as well.

You can do so in 2 ways.

The first is to assign an object to module.exports, which is an object provided out of the box by the module system, and this will make your file export just that object:

const car = {
  brand: 'Ford',
  model: 'Fiesta'
}

module.exports = car

//..in the other file

const car = require('./car')

The second way is to add the exported object as a property of exports. This way allows you to export multiple objects, functions or data:

const car = {
  brand: 'Ford',
  model: 'Fiesta'
}

exports.car = car

or directly

exports.car = {
  brand: 'Ford',
  model: 'Fiesta'
}

And in the other file, you’ll use it by referencing a property of your import:

const items = require('./items')
items.car

or

const car = require('./items').car

What’s the difference between module.exports and exports?

The first exposes the object it points to. The latter exposes the properties of the object it points to.

Lessons in this unit:

0:	Introduction
1:	How to fix "cannot use import statement outside a module"
2:	How to fix "__dirname is not defined in ES module scope"
3:	How to fix the error "unexpected token "{". import call expects exactly one argument"
4:	How to enable ES Modules in Node.js
5:	How to use .env files in Node.js with import syntax
6:	How to use import in Node.js
7:	▶︎ Expose functionality from a Node file using exports