DEV Community: R.Shobika CSE

ARRAYS IN JS PART - 1

R.Shobika CSE — Wed, 15 Jul 2026 12:51:40 +0000

ARRAY

Array is one of the object in the JavaScript. In array we can store multiple values in different datatype.

Why uses Array ?

If there is a list of items we can store in a single variable .

without an array

let num1=10;
let num2=20;
let num3=30;
let num4=40;

In this code we declare the num1,num2,num3 and num4 variable to initialize the four number. If we use the array means we can store all the number in a single variable.

const num = [10,20,30,40];

ARRAY SYNTAX

const arrayname [item1,itme2,.....];

Using JavaScript Keyword new

const arrayname = new (item1,item2,....);

How to accessing the array elements

Array can be access by the referring index number. If we want to access the single the element in array means,

console.log(arrayname(referring index number));

example program

const num = [10,20,30,40];
console.log(num[2]);

output:
30

In the above code num variable store the 4 number. In array the index value will be starting in 0 .So num = [10,20,30,40],
index value of 10 is 0
index value of 20 is 1
index value of 30 is 2
index value of 40 is 3
so what the output value is 30.

const num = [10,20,30,40];
console.log(num[num.length-1]);

output:
40

In these code we access the last element of the array. By using the formula (arrayname[arrayname.length-1]).
In the above code num = [10,20,30,40] the index start from 0,1,2,3 actually there are 4 num and length is also 4 so length-1 means we can access the last element in the array .

const num = [10,20,30,40];
for (let i =0;i<5;i++){
console.log(num[i]);
}

output:
10
20
30
40

In the above code we are access the all the element in the array by using the for loop.

To be Discussed

Array convert into String
Display the array using json
Array element can be a object

CONSTRUCTOR IN JAVASCRIPT

R.Shobika CSE — Tue, 14 Jul 2026 11:50:03 +0000

CONSTRUCTOR
The constructor in JavaScript is automatically called when the object is created. Constructor name should be start in the uppercase. Constructor is a initialization object specific value. It will reduce the repetition line of object creation.

NORMAL OBJECT CREATION

const tv1={
price:50000,
brand:"samsung"
}
const tv2={
price:60000,
brand:"Sony"
}
const tv3 ={
price:70000,
brand:"LG"
}

In this code the price and brand are repeated in all the object so instead of these we can use the constructor to reduce the code

CONSTRUCTOR

const tv1= new Tv(50000,"samsung");
const tv2= new Tv(60000,"Sony");
const tv3= new Tv(70000,"LG");

function Tv(price,brand){
this.price=price;
this.brand=brand;
}

In these code the function will call automatically once the object is created.
"this" refer to the current object

OBJECT PART - 1

R.Shobika CSE — Mon, 13 Jul 2026 16:09:45 +0000

OBJECT

In JavaScript object contains a information. it will show as a key value pair it is used for a structured and well design for easy to identify . Object is a Non primitive datatype , Its contain Properties and method

const mobile={
name : "redme",
price : 20000,
storage: 512
}

const mobile1 = {
name : "samsung",
price : 30000.
storage : 216,
}

The Above coding is the Object creation

How to print a object ?

Same patten console.log but here we have to call the value

console.log(mobile);

It will print all the values in the mobile . If you want price only means.

console.log(mobile.price);

we have to use the dot operator .

Nested Object

const mobile={
name : "redme",
price : 20000,
storage: {
ram:8,
rom:256,
}
}
console.log(mobile.storage.ram)

output:
8

Object - function (Method)

const mobile={
name : "redme",
price : 20000,
storage: {
ram:8,
rom:256,
},
browser:function(){
console.log("5g speed");
}
}
mobile.browser();

output:
5g speed

FUNCTIONS OF JS PART -2

R.Shobika CSE — Mon, 13 Jul 2026 13:54:33 +0000

VERSIONS OF FUNCTION

There are 3 version of function are

NAMED Function
Anonymous Functions

3.Arrow Function

NAMED FUNCTION

Named Function is a function it has a own name to declare the function , it is easy to understand and reuse when the debug is occurred.

function greeting(name){
return "welcome" + name;
}
greeting(shobika);

output:
welcome shobika

Anonymous Functions
This function is does not defined the explicit name of the function , it is commonly used as a callback .

const greeting = function(name){
return "welcome" + name ;
}
greeting(ram);

output:
welcome ram.

ARROW FUNCTION
A new way to write functions using the => syntax. They are shorter and do not have their own this binding. it is the easiest way to write the function.

const greet= name=> "welcome" + name ;
console.log(greet("kumar"));

output:
welcome kumar

HOISTING
Hoisting in the JavaScript is when an output statement, variable declaration or a function calling in top of the scope is called a hoisting

console.log(i);
var i =10;

output:
undefined

SCOPE
There are 2 types of scope

Local Scope
Global Scope

In Local Scope there are a 2 type

Function Scope
Block Scope

BLOCK SCOPE FUNCTION SCOPE GLOBAL SCOPE

let                   let                  let

const                 const                const

  _                    var                  var

FUNCTIONS OF JS PART -1

R.Shobika CSE — Wed, 08 Jul 2026 10:46:11 +0000

FUNCTION

JavaScript function is a reusable block of code designed to perform a specific task executed when it is called.

SYNTAX

function functionname(Parameters)
{
---------
---------
}
functionname(Arguments)

EXAMPLE PROGRAM

function stddetail(rollno,phno)
{
console.log(rollno,phno);
console.log("RAM");
}
stddetail(46,1234567890);

output:
46
1234567890
RAM

LOOPING PART - 2

R.Shobika CSE — Wed, 08 Jul 2026 10:04:19 +0000

FOR LOOP

For loop is also similar to the while loop. In while loop the we have to give the initialization, Condition, Increment/ Decrement in a multiple line but in for loop we can give these all things in a single line .

SYNTAX

for(initialization, condition, increment/decrement){
-----------
-----------
}

Example Program

for(let i=1;i<=5;i++){
console.log(i);

output:
1
2
3
4
5

Not only compulsory we should have to give in the single line we can also give like this also

let i=1;
for( ; i<=5; )
{
console.log(i);
i++;
}

output:
1
2
3
4
5

Both the for and while are called as aentry check

*do while *

The do...while statements combo defines a code block to be executed once, and repeated as long as a condition is true.

SYNTAX

do{
------
------
}while(condition)

EXAMPLE PROGRAM

let i=5;
do{
console.log("Hello");
i++;
}while(i<5)

output: Hello

The do while loop is called as a exit check

TASK

R.Shobika CSE — Tue, 07 Jul 2026 12:48:11 +0000

Task

Calculate the one student subject mark. If the student pass means calculate the total, average, grade . If the student was fail in any one of the subject means the student is fail.

let tam=85;
let eng=90;
let mat=90;
let sci=75;
let soc=100;
let total;
let avg;
if(tam>=35 && eng>=35 && mat>=35 && sci>=35 && soc>=35){
console.log("PASS");
total=tam+ eng + mat + sci + soc;
avg=total/5;
if(avg>=90){
console.log("A");
}
else if(avg>=80){
console.log("B");
}
else if(avg>=70){
console.log("C");
}
else if(avg>=60){
console.log("D");
}
else{
console.log("No Grade");
}
}
else{
console.log("FAIL");
}
console.log("total" + total);
console.log("avg" + avg);

output:
PASS
total 440
avg 88
B

Using while loop print the number 12345

let i=1;
while(i<=5){
console.log(i);
i++;
}

output:
1
2
3
4
5

3.Using while loop print "Hi" in 5 times

let j=1;
while(j<=5){
console.log("Hi");
i++;
}

output:
Hi
Hi
Hi
Hi
Hi

4.Using while loop print the number 12345 in reverse 54321.

let k=5;
while(k>=1){
console.log(k);
k--;
}

output:
5
4
3
2
1

LOOPING PART - 1

R.Shobika CSE — Mon, 06 Jul 2026 11:12:27 +0000

WHILE LOOP

The While loop is a looping condition it will execute a code until the condition is false.

SYNTAX:

while(condition){
------------
------------
}

Example Program:

let i=1;
while(i<=5){
console.log(i);
i++;
}

output:
1
2
3
4
5

CONDITIONAL STATEMENT PART - 2

R.Shobika CSE — Mon, 06 Jul 2026 11:02:27 +0000

NESTED IF - STATEMENTS: If you have if statement inside if statement is called nested if.

SYNTAX:

if (condition){
---------
if(condition){
--------
}
}

Example Program:

let mark = 90;
let attendance = 75;
if (mark>=85){
if (attendance>=80){
console.log("pass");
}
}
else{
console.log("fail");
}

output: pass

SWICTH STATEMENT

The switch case statement in JavaScript is also used for decision-making purposes. In some cases, using the switch case statement is seen to be more convenient than if-else statements.

Example Program:

let value=4;
switch(value){
case 1:
console.log("FAN");
break;
case 2:
console.log("TV");
break;
case 3:
console.log("AC");
break;
case 4:
console.log("LIGHT");
break;
default:
console.log("There is no switch");
break;
}

output: LIGHT

(If we doesn't give the break for each end of the cases means it will print all the result until when there is a break )

Example Program:

let value=2;
switch(value){
case 1:
console.log("FAN");
break;
case 2:
console.log("TV");

case 3:
console.log("AC");

case 4:
console.log("LIGHT");

default:
console.log("There is no switch");
break;
}

output :TV
AC
LIGHT
There is no switch

Incase we give the value 5 means it will display the there is no switch because there is no case 5 there is only case 1 to case 4 so it will display the default .

In some cases if we doesn't give the default and that time also we give the value 5 means it will display the undefined because there is no default .

TERNARY OPERATOR:

The Ternary Operator is a shortcut for the Conditional statement.

SYNTAX:

condition? true:false

Example Program:

let mark = 45 
let result = mark>=35?"pass":"fail"

output: pass

Reference:(http://geeksforgeeks.org/javascript/control-statements-in-javascript/)

CONDITIONAL STATEMENT PART - 1

R.Shobika CSE — Sun, 05 Jul 2026 05:55:14 +0000

CONDITIONAL STATEMENT

In JavaScript Conditional statement is used to make a decision in program. It will execute the flow of program whether the condition is true means it return TRUE otherwise it return FALSE.

Conditional statement is work on comparison and logical operator

There are some types of Conditional Statements like [if, else if]

IF- STATEMENT

In JavaScript, the if statement executes a block of code only if a specified condition evaluates to true. Use the else statement to specify a block of code to be executed if a condition is false.

let mark=32
if (mark>=35){
console.log("pass")
}else{
console.log("fail")
}

output: fail

ELSE IF - STATEMENT

In JavaScript the Else if condition is a new condition it execute when the first condition is false .

let mark =78
if(mark>=90){
console.log("A")
}
else if (mark>=75)
{
console.log("B")
}
else if (mark>=50){
console.log("C")
}
else{
console.log("fail")
}

output : B

COMPARISON OPERATOR

R.Shobika CSE — Sat, 04 Jul 2026 15:45:35 +0000

COMPARISON OPERATOR

This operator is used for to compare two values . Comparison operator always return true or false. There are various type [==, <, >, <=, >=, ===, !=, !==]

1. ==

This operator is used for to compare two value if right side and left side values are same means it return true otherwise return false.

10==10

output:true

10==5

output:false

10=="10"

output:true

2.===

This operator is used for to compare both the same value and also their datatype

10===10

output:true

10==="10"

output:false

3.<

This operator is used to find the value is less than or not is compare to the given value

10<5

output:false

10<12

output:true

4.>

This operator is used to find the value is greater than or not compare to the given value

5>10

output:false

5.<=

This operator is used to find the value is less than or equal to is compare to the given value if it is not less than or not equal to means it returns false

10<=10

output:true

6.>=

This operator is used to find the value is greater than or equal to is compare to the given value if it is not greater than or not equal to means it returns false

11>=10

output:true

7.!=

This operator is not equal to if the two value is not equal to means it returns true otherwise it return false

10!=10

output:false

10!=5

output:true

8.!==

This operator is not double equal to this operator is used to check the value is not equal and its check their data type also

10!=="10"

output:false

LOGICAL OPERATOR

Logical operators are used to combine boolean expressions. there are two type [&&,||]

1. &&

This operator is *AND * operator when both side condition is true means it return true otherwise if any one condition id false means the result is false.

Quick Remember
False False = False
False True = False
True False = False
True True = True

2.||

This operator is OR operator if any one condition is true means it return true otherwise it return false

Quick Remember
False False = False
False True = True
True False = True
True True = True

Variables

R.Shobika CSE — Thu, 02 Jul 2026 15:48:02 +0000

TYPES OF VARIABLES:
In Javascript there are 4 types of variables

Automatically: Undeclared variables are automatically declared variable. It is not basically recommended because we can reinitialize but we can't see the different like where we declare and where we reinitialize for.eg., x=5; y=6; res=x+y;
var: var variables are also similar to the automatically variables same like that we cant see the different between the declare and reinitialize for.eg., var x=5; var y=6; var res=x+y;
let: let variable are used in JavaScript commonly. In this type we can reinitialize and also we see the difference . when we reinitialize should not give again the variable type . We only give variable name like for.eg., let x=7; x=8;

4.const:
const variable is used in JavaScript. In this type we cannot reinitialize because const variable is a constant type we can't change that
for.eg.,
const y=8;

HOW TO WRITE A JS?

 In HTML code in <body> tag we have to give <script> tag like internal CSS. In CSS we give <style> same like that in JS we have to give <script>. In that script tag we have to write the code .

html
<body>
<script>
 let x=8
 let y=9
 let res=x+y
</script>
</body>

OPERATIONS:

1.ARITHMETICS OPERATION:

   Arithmetic operation is the normal mathematical calculation .In this operations there are various types [+,-,*,/,%]

(i)Addition:

let x=5
let y=7
console.log(x+y)

Output:12

let x=5
let y="7"
console.log(x+y)

Output:57
(This method is called concatenation method. In + there are two method one is normal add . if we give two number means it do a addition calculation . if we give one number and one string means it do a concatenation . concatenation means it will combines the values).

(ii) Subraction:

let x=5
let y=8
console.log(x-y)

output:3

let x=5
let y="8"
console.log(x-y)

output:3

(This method is not a concatenation . In addition only it will concatenate if otherwise string will consider as a number )

(iii) Multiplication:

let x=5
let y=8
console.log(x*y)

output:40

let x=5
let y="8"
console.log(x*y)

output:40

( This method is not a concatenation . In addition only it will concatenate if otherwise string will consider as a number ).

** (iv)Division:**

  Normal mathematical division but it does not take a remainder it will take quotient value

let x=4
let y=2
console.log(x/y)

output:2

let x=4
let y="2"
console.log(x/y)

output:2

(This method is not a concatenation . In addition only it will concatenate if otherwise string will consider as a number ).

(v).Modulus:

 In this operation it also like a division but it will take the remainder answer

let x=4
let y=2
console.log(x%y)

output:0

let x=4
let y="2"
console.log(x%y)

output:0

( This method is not a concatenation . In addition only it will concatenate if otherwise string will consider as a number ).

2. INCREMENT/DECREMENT OPERATORS:

In this operator there are 2 types
1. Post Increment/decrement (i++)
2. Pre Increment /decrement (++i)

(i). Post Increment/decrement:

  In this increment/decrement the increment/decrement value store in the memory then if we give the next line print statement means it will show the increment/decrement value

let i=9;
 i++

output:9

The output will be the 9 not 10 because it is a post increment/decrement so what the output value is 9 the 10 will be store in the memory.

(ii). Pre Increment/decrement:

  In this increment / decrement the increment/decrement value show in the output .

 let i=9;
    ++i;

output:10

the output will be the 10 not 9 because it is pre increment/decrement so what the output value is 10 not 9.