Exporting and Importing Module in node.js

Using a simple module in node.js

What is a node.js module (link to article (opens new window)):

A module encapsulates related code into a single unit of code. When creating a module, this can be interpreted as moving all related functions into a file.

Now lets see an example. Imagine all files are in same directory:

File: printer.js

"use strict";

exports.printHelloWorld = function (){
    console.log("Hello World!!!");
}

Another way of using modules:

File animals.js

"use strict";

module.exports = {
    lion: function() {
        console.log("ROAARR!!!");
    }

};

File: app.js

Run this file by going to your directory and typing: node app.js

"use strict";

//require('./path/to/module.js') node which module to load
var printer = require('./printer');
var animals = require('./animals');

printer.printHelloWorld(); //prints "Hello World!!!"
animals.lion(); //prints "ROAARR!!!"

Exporting with ES6 syntax

This is the equivalent of the other example (opens new window) but using ES6 instead.

export function printHelloWorld() {
  console.log("Hello World!!!");
}

Using Imports In ES6

Node.js is built against modern versions of V8. By keeping up-to-date with the latest releases of this engine, we ensure new features from the JavaScript ECMA-262 specification are brought to Node.js developers in a timely manner, as well as continued performance and stability improvements.

All ECMAScript 2015 (ES6) features are split into three groups for shipping, staged, and in progress features:

All shipping features, which V8 considers stable, are turned on by default on Node.js and do NOT require any kind of runtime flag. Staged features, which are almost-completed features that are not considered stable by the V8 team, require a runtime flag: --harmony. In progress features can be activated individually by their respective harmony flag, although this is highly discouraged unless for testing purposes. Note: these flags are exposed by V8 and will potentially change without any deprecation notice.

Currently ES6 supports import statements natively Refer here (opens new window)

So if we have a file called fun.js…

export default function say(what){
  console.log(what);
}

export function sayLoud(whoot) {
  say(whoot.toUpperCase());
}

…and if there was another file named app.js where we want to put our previously defined functions to use, there are three ways how to import them.

Import default

import say from './fun';
say('Hello Stack Overflow!!');  // Output: Hello Stack Overflow!!

Imports the say() function because it is marked as the default export in the source file (export default …)

Named imports

import { sayLoud } from './fun';
sayLoud('JS modules are awesome.'); // Output: JS MODULES ARE AWESOME.

Named imports allow us to import exactly the parts of a module we actually need. We do this by explicitly naming them. In our case by naming sayLoud in curly brackets within the import statement.

Bundled import

import * as i from './fun';
i.say('What?'); // Output: What?
i.sayLoud('Whoot!'); // Output: WHOOT!

If we want to have it all, this is the way to go. By using the syntax * as i we have the import statement provide us with an object i that holds all exports of our fun module as correspondingly named properties.

Paths

Keep in mind that you have to explicitly mark your import paths as relative paths even if the file to be imported resided in the same directory like the file you are importing into by using ./. Imports from unprefixed paths like

import express from 'express';

will be looked up in the local and global node_modules folders and will throw an error if no matching modules are found.