There is no GUI in Node.js, no HTML or CSS. This also means there aren't any scipt tags to include JS files into our application. Node.js uses modules to to share your JavaScript with other JavaScript in your apps. No window or globals needed. If you've ever done window.App = window.App || {} then you'll like this!

What is a module

A module is a reusable chunk of code that has its own context. That way modules can't interfere with or polute the global scope.

You can think of them like lego blocks that you can create, import, and share.

Two module types

By default, Node.js uses common js modules. With newer versions of Node.js we can now take advantage of ES6 modules. To opt into using this syntax, you can use the .mjs extension instead of .js. We'll be using the ES6 module syntax going forward as they are the standard now with browsers adding support now.

Module syntax

Now, let's create our first module. The only thing we have to do is expose some code in one for our JavaScript files. We can do that with the export keyword.

// utils.js
export const action = () => {

}

export const run = () => {

}

// app.js

import { action, run } from './utils'

Few things happening here. Let's look at the utils.js file. Here we're using the export keyword before the variable declartion. This creates a named export. With the name being whatever the variable name is. In this case, a function called action. Now in app.js, we import the action module from the utils file. The path to the file is relative to the file you're importing from. You also have to prefix your path with a './'. If you don't, Node will think you're trying to import a built in module or npm module. Because this wa a named export, we have to import with brackets { action, run } with the exact name of the modules exported. We don't have to import every module that is exported.

Usually if you only have to expose one bit of code, you should use the default keyword. This allows you to import the module with whatever name you want.

// utils.js
default export function () {
  console.log('did action')
}

// app.js
import whateverIWant from './utils'

You can read more about the module syntax on the Node.js docs.

Internal Modules

Node.js comes with some great internal modules. You can think of them as like the phenonminal global APIs in the browser. Here are some of the most useful ones:

• fs - useful for interacting with the file system.
• path - lib to assit with manipulating file paths and all their nuiances.
• child_process - spawn subprocesses in the background.
• http - interact with OS level networking. Useful for creating servers.