Backend in NodeJS

Getting Started

1. Welcome

• Complete Node course

2. What is Node

• Also known as NodeJS
• Open Source
• Cross Platform runtime environment
• Execute Javascript code outside of a browser
• Used to build backend services known as Application Programming Interfaces (APIs) that power the client applications (web app inside a web browser or mobile app running inside a mobile device) seen and interacted with by the user (just a surface)
• Services sitting on a server or in the cloud interact with the client applciations to store data, send emails, push notifications, kick of workflows
• Ideal for building fast, highly scalable, data-intensive, real-time apps to power client applications
• Easy to get started
• Used for prototyping and agile development
• Build superfact and highly scalable services
• Used in production by large companies
• Easy for Javascript developers to learn
• Largest ecosystem of open-source libraries

3. Node Architecture

• Javascript code that runs inside a browser that provides a runtime environment
• Browser has a Javascript Engine that converts Javascript code to Machine code
• Edge uses Chakra
• Firefox uses SpiderMonkey
• Chrome uses v8 (fastest Javascript Engine)
• Javascript behaves differently in different browsers
• The "document" object provides an environment in which the code can run but not present inside Node
• The v8 engine inside a C++ program is Node.exe that executes the Javascript code present in the environment provided by Node
• The "fs" object helps with working on file system
• The "http" object helps in listening to requests
• The environment provided by Node is different from the Chrome environment but the v8 engine is same
• Node is neither a language nor a framework

4. How Node Works

• The non-blocking/asynchronous nature of Node
• Single thread is used to handle multiple requests
• ASP.NET and Rails are synchronous nature where a single thread waits for a request to be completed before moving on to the next request
• Wait for availablity of threads in case of synchronous types of frameworks
• While a single thread is executing a query in the databse as a part of a request, it will also be used for another request while the query is executing
• Result of each request is put in an event queue and when Node finds it data-ready, it will process it
• Built for applications involving disk, network access, I/O intensive, realtime, data-intensive applications
• Not used for CPU-intensive applications like video encoding, image manipulation service as calculations are done by CPU

5. Installing Node

• To check the existance and version of node

node --version

6. Your First Node Program

• To run a javascript file (i.e. app.js)

node app.js

• Browser environement objects like window and document do not exist
• Other objects to work with files, operating system, network

7. Course Structure

• This README is in order of the course structure

Node Module System

1. Introduction

• Learn about the Node Module System and different modules in the core of Node like os, fs, events, http
• Create own modules

2. Global Object

• Used log function to log on the console

console.log()

• The console object is a global object (can be accessed anywhere)
• Some global functions are setTimeout() (used to call after a delay), clearTimeout(), setInterval() (repeatedly call a function after an interval), clearInterval() (Used to stop calling the function repeatedly)
• Browsers have window object that represents global scope
• The function "console.log()" is prefixed automatically by the Javascript engine with "window" so it is treated like "window.console.log()"
• The below code declaring a variable like "var x = 1" is also present in the window object like "window.x" which is 1 in this case
• In Node, window object is not present
• Use "global" in Node but this does not store variables

3. Modules

• A function defined in browser can be overwritten by the function of the same name declared in another file
• The "window" object overwrites the function
• Building modules (encapsulation) eleminates overwriting of functions and variables
• Every file in Node is a module and the functions and variables are private to the module
• The export is used to use functions and variables outside a module by making it public
• The "module" object is not global

4. Creating a Module

• Create a file having a function and a variable and print the module to check the exports in that file
• Use the following to get the list of exports in a module

console.log(module);

5. Loading a Module

• Use the require() function to load a module that is not present in browsers
• Requires path of the module to be loaded
• Use "const" to store the module
• Use "jshint" to get the errors in the module

jshint app.js

• The export of single fnction instead of object

module.exports = log;

6. Module Wrapper Function

• Code inside a file is wrapped inside a function by default that has many parameters local to the module
• IIFE (Immediately-invoked Function Expression) is the function and is used to create the scope

7. Path Module

• Useful inbuilt modules in Node like filesystem, http, query strings, path, os, process, stream
• Arguement without path in require() function is assumed to be a built-in module in Node
• The "path" module has a function called parse() that helps in getting details of the path

8. OS Module

• Many in-built functions like freemem(), totalmem(), userInfo(), uptime()
• Use of ECMA Script (or ES6 or ES2015)

var totalMemory = os.totalmem();
console.log(`Total Memory: ${totalMemory}`);

• Node helps in executing code outside of the browser

9. File System Module

• Working with files using the "fs" module
• Functions in "fs" of synchronous and asynchronous type
• Use asynchronous functions in applications to serve many clients
• Requires a function as an arguement that is called after the asynchronous process is completed (a callback)

10. Events Module

• Event is a signal that something occured in the application
• Event is raised in Node
• Event contains many classes (container for properties and functions also known as methods)
• Class is used by making a new object of it
• Classes define the properties and behaviour
• Actual instance of a class is an object
• The emit() function is used to raise an event or raise a signal
• The listener function is called when a signal is raised
• The listner contains a callback function that is executed when the signal is raised or the event is triggered
• The event or signal is raised after registering a listner
• The event calls all the listners to check the appropriate listner in a synchronous manner

11. Event Arguements

• Emitter sending data about the event to the listner
• Sending data in the form an encapsulation or an object called event arguement
• The "function" keyword is eliminated and the arguements are seperated with the body by the arrow function or "=>"

12. Extending EventEmitter

• The EventEmitter object is rarely used
• Create and use class having all capabilities of the EventEmitter class
• Function inside a class is a method

13. HTTP Module

• Creating network in applications
• Server listens on port number and raises an event whenever there is a new request
• Code gets more complex using "http" module
• Use "express" instead

Node Package Manager (NPM)

1. Introduction

• NPM is installed with Node
• To check the NPM version

npm -v

2. Package.json

• JSON file to include basic information about the application
• Meta-data about the application
• Present in every node application
• To create package.json

npm init --yes

• Every node module has its own package.json

3. Installing a Node Package

• Use NPM to install packages from NPM registry
• To install NPM packages like underscore

npm i underscore

• Installed packages are in dependencies in the package.json

4. Using a Package

• To use the underscore library

var _ = require('./underscore');

• Without path, it is assumed as a core module else it is treated as a file path

5. Package Dependencies

• Other libraries installed automatically is because a module requires many other modules to refer to

6. NPM Packages and Source Control

• The "node_modules" folder is big as it has all the installed packages and their dependencies and it is not advised to add it into the repository
• All dependencies in present in package.json file

npm i

• Use ".gitignore" to store folder and file names not be included in repository

7. Semantic Versioning

• Semantic versioning is to divide the version in 3 parts or numbers called Major version, Minor version, Patch release (used in bug fixing)
• Patch release number increases as and when bugs are fixed
• Minor version number is to create changes in the package without creating any change in APIs
• Major version number is to create changes in the package along with change in APIs
• Carat character is used to suggest the minium major version for the application
• Carat character is used to suggest the minium major version and minor version for the application

8. Listing the Installed Packages

• To see the entire list of packages and their versions

npm list

• To get the versions of the installed packages

npm list --depth=0

9. Viewing Registry Info for a package

• Meta-data about the packages like mongoose

npm view mongoose

• Dependencies about the packages like mongoose

npm view dependencies

10. Installing a Specific Version of a Package

• To install a specific version like "2.4.2" for a package like mongoose

npm i [email protected]

11. Updating Local Packages

• Checking the packages and their current, wanted and latest versions

npm outdated

• Update to the latest versions where only minor versions and the patch numbers are updated

npm update

• To check the latest versions, use npm-check-updates

npm-check-updates

• To update the package.json to the latest versions

ncu -u

• To install the updates

npm i

12. DevDependencies

• Packages used only during development not be in production
• Static tool used to find problems in code under devDependencies

npm i jshint --save-dev

13. Uninstalling a Package

• To uninstall a package like mongoose

npm un mongoose

14. Working with Global Packages

• Not project or folder specific like npm, ng
• Usually a command line tool
• Use "-g" flag to install or uninstall globally

npm i -g [email protected]

• To upgrade to the latest

npm i -g npm

15. Publishing a Package

• Create a package.json file

npm init --yes

• Create an account

npm adduser

• Login to npm

npm login

• To publish

npm publish

• Make the name of the package unique in package.json to publish the package
• Has its own properties by npm in package.json of published package

16. Updating a Published Package

• Can not publish over previously published
• Change version number to avoid error
• To change the version number

npm version major

or

npm version minor

or

npm version patch