Introduction to Node JS

Concepts in Focus

• MERN Stack
• Node JS
• Running JavaScript Using Node JS
• Node REPL (Read-Eval-Print-Loop)
• Node CLI
• Module
• Common JS Module Exports
• Modern JS Module Exports

1. MERN Stack

MERN stands for MongoDB, Express JS, React JS and Node JS.

It is a JavaScript Stack that is used for easier & faster deployment of full-stack web applications.

2. Node JS

Node JS is a JavaScript environment that executes JavaScript code outside a web browser.

Why Node JS?

• Cross-Platform (Windows, Linux, Mac OS X, etc.)
• Huge number of third-party packages
• Open Source
• Massive Community

3. Running JavaScript Using Node JS

We can run JavaScript using Node JS in 2 ways.

• Node REPL (Similar to browser console)
• Node CLI

3.1 Node REPL (Read-Eval-Print-Loop)

Type

node

in the terminal and press

Enter

.

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root@123# node

Welcome to Node.js v12.18.3.

Type ".help" for more information.

> const a = 1

undefined

> const b = 2

undefined

> a+b

3

>

Type

.exit

and press

Enter

to exit from the Node REPL.

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root@123# node

Welcome to Node.js v12.18.3.

Type ".help" for more information.

> const a = 1

undefined

> const b = 2

undefined

> a+b

3

> .exit

root@123:/home/workspace#

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3.2 Node CLI

We can write JavaScript to a file and can run using Node CLI.

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//index.js

const greetings = (name) => {

console.log(`Hello ${name}`);

};

greetings("Raju");

greetings("Abhi");

JAVASCRIPT

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root@123# node index.js

Hello Raju

Hello Abhi

Note

Save the file whenever the code changes.

4. Module

In Node JS, each JavaScript file is treated as a separate module. These are known as the Common JS/Node JS Modules.

To access one module from another module, we have Module Exports.

• Common JS Module Exports
  • Default Exports
  • Named Exports
• Modern JS Module Exports
  • Default Exports
  • Named Exports

4.1 Common JS Module Exports

4.1.1 Default Exports

Exporting Module

The

module.exports

is a special object included in every JavaScript file in the Node JS application by default.

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//calculator.js

const add = (a, b) => {

return a + b;

};

module.exports = add;

JAVASCRIPT

Importing Module

To import a module which is the local file, use the require() function with the relative path of the module (file name).

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//index.js

const add = require("./calculator");

console.log(add(6, 3));

JAVASCRIPT

Output

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root@123# node index.js

9

4.1.2 Named Exports

We can have multiple named exports per module.

Exporting Module

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//calculator.js

const add = (a, b) => {

return a + b;

};

const sub = (a, b) => {

return a - b;

};

exports.add = add;

exports.sub = sub;

JAVASCRIPT

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Importing Module

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//index.js

const { add, sub } = require("./calculator");

console.log(add(6, 3));

console.log(sub(6, 3));

JAVASCRIPT

Output

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root@123# node index.js

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3

4.2 Modern JS Module Exports

Modern JS Modules are known as ES6 Modules.

The export and import keywords are introduced for exporting and importing one or more members in a module.

4.2.1 Default Exports

Exporting Module

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//calculator.mjs

const add = (a, b) => {

return a + b;

};

export default add;

JAVASCRIPT

Importing Module

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//index.mjs

import add from "./calculator.mjs";

console.log(add(6, 3));

JAVASCRIPT

Output

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root@123# node index.mjs

9

4.2.2 Named Exports

Exporting Module

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//calculator.mjs

export const add = (a, b) => {

return a + b;

};

export const sub = (a, b) => {

return a - b;

};

JAVASCRIPT

Importing Module

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//index.mjs

import { add, sub } from "./calculator.mjs";

console.log(add(6, 3));

console.log(sub(6, 3));

JAVASCRIPT

Output

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root@123# node index.mjs

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3

Note

• We need to specify 
  .mjs
   extension while importing ES6 Modules.
• We may or may not need to specify 
  .js
   while importing Common JS Modules.