javascript.md

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About Javascript

Javascript(JS) is a object-oriented programming language which adhere to ECMA Script Standards. Javascript is required to design the behaviour of the web pages.

Key Features

• Open-source
• Just-in-time compiled language
• Embedded along with HTML and makes web pages alive
• Originally named as LiveScript.
• Executable in both browser and server which has Javascript engines like V8(chrome), SpiderMonkey(Firefox) etc.

Syntax help

STDIN Example

varreadline=require('readline');varrl=readline.createInterface({input: process.stdin,output: process.stdout,terminal: false});rl.on('line',function(line){console.log("Hello, "+line);});

variable declaration

Keyword	Description	Scope
var	Var is used to declare variables(old way of declaring variables)	Function or global scope
let	let is also used to declare variables(new way)	Global or block Scope
const	const is used to declare const values. Once the value is assigned, it can not be modified	Global or block Scope

Backtick Strings

Interpolation

letgreetings=`Hello ${name}`

Multi line Strings

const msg = `
hello
world!
`

Arrays

An array is a collection of items or values.

Syntax:

letarrayName=[value1,value2,..etc];// orletarrayName=newArray("value1","value2",..etc);

Example:

letmobiles=["iPhone","Samsung","Pixel"];// accessing an arrayconsole.log(mobiles[0]);// changing an array elementmobiles[3]="Nokia";

Arrow functions

Arrow Functions helps developers to write code in concise way, it’s introduced in ES6. Arrow functions can be written in multiple ways. Below are couple of ways to use arrow function but it can be written in many other ways as well.

Syntax:

()=>expression

Example:

constnumbers=[0,1,2,3,4,5,6,7,8,9]constsquaresOfEvenNumbers=numbers.filter(ele=>ele%2==0).map(ele=>ele**2);console.log(squaresOfEvenNumbers);

De-structuring

Arrays

let[firstName,lastName]=['Foo','Bar']

Objects

let{firstName, lastName}={firstName: 'Foo',lastName: 'Bar'}

rest(...) operator

const{
title,
firstName,
lastName,
...rest}=record;

Spread(...) operator

//Object spreadconstpost={
...options,type: "new"}//array spreadconstusers=[
...adminUsers,
...normalUsers]

Functions

functiongreetings({ name ='Foo'}={}){//Defaulting name to Fooconsole.log(`Hello ${name}!`);}greet()// Hello Foogreet({name: 'Bar'})// Hi Bar

Loops

1. If:

IF is used to execute a block of code based on a condition.

Syntax

if(condition){// code}

2. If-Else:

Else part is used to execute the block of code when the condition fails.

Syntax

if(condition){// code}else{// code}

3. Switch:

Switch is used to replace nested If-Else statements.

Syntax

switch(condition){case'value1' :
//code[break;]case'value2' :
//code[break;].......
default :
//code[break;]}

4. For

For loop is used to iterate a set of statements based on a condition.

for(Initialization;Condition;Increment/decrement){//code }

5. While

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while(condition){// code }

6. Do-While

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do{// code }while(condition);

Classes

ES6 introduced classes along with OOPS concepts in JS. Class is similar to a function which you can think like kind of template which will get called when ever you initialize class.

Syntax:

classclassName{constructor(){ ... }//Mandatory Class methodmethod1(){ ... }method2(){ ... }
...
}

Example:

classMobile{constructor(model){this.name=model;}}mbl=newMobile("iPhone");