Mongo DB, Express, React, Node - All three utilizes javascript

Version: Both js and ts belongs to ES

ES -

dataType: Frist thing to check in any language

String : '' or " " (any thing in a quote is String)

Number : 23, 23.232, 232422424

Boolean : true or false

null

undefined

variable:

defing a variable:

var a = 'ds'

var b = 2244

var c = true

Typeof is inbuilt method in the javascript which tells the typeof variable

modules of smaller to larger is always smaller

2%3 = 2

6%7 = 6

if we add + with string it with Concate

String + string = String

number + number = number

string + number = string

number + string = string

if both the side is a pure number as string or number with + they will Concate

but with , * / it will do the operation

true is eqaul to 1

false is eqaul to 0

true + true

true + 10

'hai'+ true

= Assingment

== compare the data

=== compare the data and dataType

JavaScript is caseSensitive

console.log('this is mydata')

alert('just for notification');

comfirm('do u want to leave?')

ok = true

cancel = false

prompt('to take the user input')

it will take the value which is Submitted by the user

it will return as the string from input box or prompt or anything

converting the string to number ==> parseInt(s)

parseInt will give u pure number

In Es6 Number is new way to conveting to number

These methods are useful for extracting the string from a larger one

it is a subset of another string.

String.substring(index A, index B), end index is optinal

Slice --- it will remove the first element in the string

var city = 'Delhi'

slice and substring gives the same result

slice(start,end?)

substring(start,end?)

substr(start,length?)

var city = 'Delhi'

city.slice(-1) // gives the last character

var str = 'this is a javascript'

multiple no of zeros for getting the random number with digits

floor is on lower side

ceil is on lower side

round is on higher side

localStorage - it is a persistant Storage(we need to remove manually)

sessionStorage - It is non persistant Storage(tab specifc)

sessionStorage.setItem('_SAFJOFA', '32452143');

it is saved bases on web URL, It is dedicated only to that particular link

it has exipry Time

var name = 'Avenger';

var rating = 3.5

var type = 'Action';

var region = 'Hollywood'

var data = "This movie name is "+ name +" has a rating of "+rating+" and belongs to "+type+" "

var data = `the movie name is ${name} has a rating od ${rating} and belongs to ${region}`

//logic

//logic

var a = 46324524551

if(a%2==0) {

console.log(`${a} is an even number);

> Its a single line if else condition

a= 10

a=10 ? a : b

var y =9

y>10? y+1 : y-1

truthy = true & 1 which is either positive or negative, except 0

falsy = false & 0 , null, undefined

let a = Date()

var b = new Date()

sunday is 0

january is 0

var name = 'Sandeep'

case 'Sandeep':

console.log('You are a user');

break;

case 'Deepu':

console.log('You are an Admin');

break;

default :

console.log('You dont have any privilages');

You are a user

var name = 'adad'

case 'Sandeep':

console.log('You are a user');

break;

case 'Deepu':

console.log('You are an Admin');

break;

default :

console.log('You dont have any privilages');

You dont have any privilages

if we don't specify break, it will pirnt the true conditon and below one's too

var num = 3.2;

switch(num%2) {

case 0:

console.log('number is even');

break;

case 1:

console.log('number is odd');

break;

default:

console.log('number is neither even nor odd')

-It is use to match the pattern

starts with ^ and ends with $ (^$)

var t = 'r'

(2) ["r", "r", index: 0, input: "r", groups: undefined]

[] - It matches the pattern for the first Character

{1} - It matches the first CharacterData

{2,4} - min 2 and max 4

+ - It matches for any length

It should start with number and rest any thing else

It is a collection of homogenous data

var a = ['a','23','daad']

var b = [1,3,4,5,3]

var c = [true,false,true]

But in JavaScript and python

It is a collection of homogenous and hetrogenous

var d = ['exmaple',23,false];

var city = ['Delhi','Hyderabad','Mumbai']

typeof(city) is an object

var city = ['Delhi','Texas','Newyork']

(4) ["Delhi", "Texas", "Newyork", "SanJose"]

(5) ["Delhi", "Texas", "Newyork", "SanJose", "extra"]

(4) ["Delhi", "Texas", "Newyork", "SanJose"]

pop(3) - pop with any index value is not counted, it only removes lst element

pop will remove at beigning

push will add at end

unshift will add at beigning

shift will remove always from beigning

(5) ["one", "Delhi", "Texas", "Newyork", "SanJose"]

(5) ["one", "Delhi", "Texas", "Newyork", "SanJose"]

(6) ["two", "one", "Delhi", "Texas", "Newyork", "SanJose"]

function greet() {

console.log('Normal function')

o/p Normal function

we need to call the function explictly to generate the output

console.log('calling IIFE')

this function will be executed on the page load without calling explicitly

we will control the flow of the function output when to show the value

function random(userInput) {

for (i=0;i<userInput; i++)

console.log(i)

function * alpha(x) {

var date = alpha(4)

data.next() // it will load the data when in need

{value: 0, done: false}done: falsevalue: 0[[Prototype]]: Object

{value: 1, done: false}

{value: 2, done: false}

{value: 3, done: false}

{value: 4, done: false}

{value: undefined, done: true}

var a = [1,234,433,54,3,4,546,65,737,67,54,6,3634,364]

a.map((data) => {return data})

(14) [1, 234, 433, 54, 3, 4, 546, 65, 737, 67, 54, 6, 3634, 364]

let's multiply the input array by 2

a.map((data) => {console.log(data*2)})

(14) [1, 234, 433, 54, 3, 4, 546, 65, 737, 67, 54, 6, 3634, 364]

VM589:1 2

VM589:1 468

VM589:1 866

VM589:1 108

VM589:1 6

VM589:1 8

VM589:1 1092

VM589:1 130

VM589:1 1474

VM589:1 134

VM589:1 108

VM589:1 12

VM589:1 7268

VM589:1 728

map will iterate and return the array...

> it will always return the same length as input array

> it is used to apply the logic as sum, multiply ..etc

FILTER:

it is use to filter the values from array.

> it may or maynot retutn the same length as input array

> it only returns those value which ouptut is true

var b=[5,11,3,6,8,23,24,15,22,13,10]

b.filter((data) => {return data >10})

(6) [11, 23, 24, 15, 22, 13]

0: 11

1: 23

2: 24

3: 15

4: 22

5: 13

b.map((data) => {return data >10})

(11) [false, true, false, false, false, true, true, true, true, true, false]

tricky q

var a=[0,1,2,3]

a.map((data) => { return data*2 })

(4) [0, 2, 4, 6]

var a=[0,1,2,3]

a.filter((data) => { return data*2 })

(3) [1, 2, 3]

var > we can able to redeclare and reassign

let > we cannot able to redeclare and can reassign

const > we cannot redeclare and reassign

clouser is something where we can close or restrict the scope

var a =10; //global scope

function add() {

var b=20; // local scope

return a+b;

console.log("ADD", add());

console.log("value of a", a);

console.log("value of b", b);

"ADD"

"ReferenceError: b is not defined

{} will consider as clouser only in the functions but not in loops.

var a =10;

for (i=0; i<10; i++) {

var b=20;

console.log(a+b+i);

console.log("value of a", a);

console.log("value of b", b);

"value of a"

"value of b"

let helps to restrict the scope...

we can call the function even before the declaration

var a

var b = null

Single object can have n number of properties

var movies = {

name : 'avengers',

rating: 3.5,

lang: 'english'

'object'

'avengers'

'english'

movies.rating = 3.9

{name: 'avengers', rating: 3.9, lang: 'english'}

> we can access the properties

> we can add a propety

> we can modify the property

> we can delete the property

JSON - having multiple objects in a array

> a way to reprsent the data

> a key value pair of the data

var movies = [

{

name : 'avengers',

rating: 3.5,

lang: 'english'

{

name : 'teal',

rating: 3.5,

lang: 'english'

{

name : 'dil',

rating: 4.5,

lang: 'telugu'

(3) [{…}, {…}, {…}]

0: {name: 'avengers', rating: 3.5, lang: 'english'}lang: "english"name: "avengers"rating: 3.5[[Prototype]]: Object1: {name: 'teal', rating: 3.5, lang: 'english'}2: {name: 'dil', rating: 4.5, lang: 'telugu'}length: 3[[Prototype]]: Array(0)

'avengers'

when a function is assigned to a variable it become method

we can call multiple times

var calc = {

sum:function(a,b) { return a+b }

sub: (a,b) => { return a-b }

var dbquery = {

find:(table) => { return `select * from ${table}` }

dbquery.find('student')

'select * from student'

this keyword refers to the above scope

var lastName = 'Scott'

var sayHi = {

firstName: 'zoe',

lastName: 'Lisa',

people:function() {

return `say hi to ${this.firstName} ${this.lastName}`

"say hi to zoe Lisa"

var bob = new Object(); ///object bob is created with no properties

bob.age = 29 // assigned age property

this.age= newAge;

var createAge = function(newAge) {

this.age = newAge

var bob = new Object();

bob.age = 29

bob.city = 'delhi'

bob.setAge = createAge

var tony = new Object();

tony.age = 29

tony.city = 'delhi'

tony.setAge = createAge

o/p

ƒ (newAge) {

this.age = newAge

{age: 29, city: 'delhi', setAge: ƒ}

{age: 28, city: 'delhi', setAge: ƒ}

function language(name,country){

this.name = name;

this.country = country;

var hindi = new language('hindi','india') // creating obj using constructor

hindi // hindi is a obj having name and country as a properties

language {name: 'hindi', country: 'india'}

class language {

constructor(name.country) {

this.name = name;

this.country = country;

}

var eng = new language('English','USA')

function human(name) { /// one arg as name

this.name = name;

this.city = 'london';

function robot(name) {.

human.prototype = new robot() //acessing the robot properties to the human

var john = new human ('joy')

robot {name: undefined, legs: 2, color: 'red'}

var chitti = new robot('robo')

robot {name: 'robo', legs: 2, color: 'red'}

john.color /// human can stil access the propeties of robot

'red'

class geo {

constructor(lan,lon) {

this.lan = 11.1331;

this.lon = 213.242;

}

class human extends geo { ///// we will use extends keyword to inhert the properties from geo