NodeJS

NodeJS Notes

Started on 11th December 2021.

---

What is NodeJS?

• NodeJS or Node is an open source and cross platform runtime environment for executing JavaScript code outside of a browser.
• We often use Node to build backend services like APIs.
• Node is ideal for building higly-scalable, data-intensive and real time apps.
• Node is not a programming language.
• NodeJS is asyncrhonous by default.
• Node is ideal for I/O-intensive apps.
• Do not use Node for CPU-intesive apps.
• Examples of CPU-intesisve: Video-Encoding, Image Manipulation Service.

---

Why NodeJS?

• NodeJS allows us to create backend using JavaScript.
• If you already know JS then for backend you need not learn yet another language and all of it intricacies.
• Node is also superfast and will allow us to create really scalable and fast running websites.
• Companies that use NodeJS: Twitter, Netflix, Trello, Uber
• Node is great for prototyping and agile development.
• Since we use JS in frontend and backend, source code will be cleaner and more consistent.
• Largest ecosystem of open-sourced libraries.

---

While importing we use const because we do not want to accidentaly change it to something else like importVar = 1;

Module Wrapper Function

Lets say logger.js had the following content:

var url = "http://mylogger.io/log";

function log(message) {
    // Send an HTTP Request
    console.log(message);
}

module.exports.log = log;

and app.js has this:

const logger = require("./logger");

logger.log("Message from app!");

• Usually when we import a module, node adds a wrapper function and that will look like this:

(function (exports, require, module, __filename, __dirname) {
    var url = "http://mylogger.io/log";

    function log(message) {
        // Send an HTTP Request
        console.log(message);
    }

    module.exports.log = log;
});

---

Video: Oe421EPjeBE - Node.js and Express.js full course

Date started: 17th December 2021

Topics covered:

• Fundamentals of Node.js

• Express.js

• MongoDB, Mongoose

• Applications

• Deployment

• The main goal of this course is to build modern, fast and scalable server-side web applications with node.

What is NodeJS?

• Environment to run JS outside of the Browser
• Created in 2009 and is build on top of Chrome's v8 JS engine
• Big community
• Full-Stack

Pre-requisites

• Basics of HTML, CSS, JS [ES6]
• Callbacks, promises, Async-await
• Youtube - Code Addict
• Playlist - JS Nuggets

Course Structure

• Introduction
• Installation
• Node Fundamentals
• Express Tutorial
• Building Apps

Difference between Browser JS & Node JS

Browser JS	Node.js
DOM	No DOM
Window	No Window
Interactive Apps	Server Side Apps
No Filesystem	Filesystem
Fragmentation	Versions
ES6 modules	Common JS

Global Variables in NodeJS

• It means that anywhere in the application you can access those variables.

• Some of those global variables are:

  • __dirname - path to current directory
  • __filename - file name
  • require - function to use modules (CommonJS)
  • module - info about current module (file)
  • process - info about env where the program is being executed

Modules in NodeJS

• Every file is a module.
• You can export multiple stuff or a single stuff.
• Multiple exports example -> module.exports = { john, peter };
• Single export example -> module.exports = sayHI;
• Single export example -> module.exports.displayHi = sayHI;

Builtin modules

• NodeJS has a lot of built-in modules
• Each module in turn has a lot of properties
• We will cover only some of the built-in stuff
  • os
  • path
  • fs
  • http

NPM

• Package, dependency and module - all mean the same - Shareable JS Code

• npm - Global command, comes with node

• npm --version - lists out the version

• To install a local dependency (to be used in a particular project)

  npm i <package name>
  

• To install a dependency globally (to be used in any project)

  npm install -g <package name>
  

• In Mac,

  sudo npm install -g <package name>
  

• package.json - manifest file (stores important info project/package)

• There are 3 ways to create package.json

• manual approach would be creating package.json in the root, creating properties, etc.,

• To install a dependency only for development purposes npm i nodemon -D

• To uninstall a package - npm uninstall bootstrap

Events in NodeJS

• Event driven programming is used heavily in NodeJS.
• First listen for an event and then emit it.

// get back the class
// if want custom extend from class
// otherwise just for emitting and handling events create instance
const EventEmitter = require("events");

const customEmitter = new EventEmitter();

// on and emit methods
// keep track of the order
// additional arguments
// built-in modules utilize it

customEmitter.on("response", (name, id) => {
    console.log(`data recieved user ${name} with id:${id}`);
});

customEmitter.on("response", () => {
    console.log("some other logic here");
});

customEmitter.emit("response", "john", 34);

Stream

• Streams are used to read or write sequentially.
• There are 4 types of streams:
  • Writeable - only writing
  • Readable - only reading
  • Duplex - both read and write
  • Transform - data can be modified while reading or writing

---

API vs SSR

API	SSR
Application Programming Interface	Server Side Rendering
API - JSON	SSR - Template
Send Data	Send Template
res.json()	res.render()