DEV Community: Athithya Sivasankarar

JavaScript Array Iteration Methods

Athithya Sivasankarar — Wed, 15 Apr 2026 16:29:52 +0000

JavaScript provides powerful array iteration methods to work with elements easily. These methods help us write cleaner and shorter code.

1. forEach()

Executes a function for each element.

let nums = [1, 2, 3];
nums.forEach(n => console.log(n));

Output:

1
2
3

2. map()

Creates a new array by modifying each element.

let nums = [1, 2, 3];
let result = nums.map(n => n * 2);
console.log(result);

Output:

[2, 4, 6]

3. flatMap()

Maps and flattens the array.

let arr = [1, 2];
let result = arr.flatMap(x => [x, x * 2]);
console.log(result);

Output:

[1, 2, 2, 4]

4. filter()

Filters elements based on condition.

let nums = [1, 2, 3, 4];
let even = nums.filter(n => n % 2 === 0);
console.log(even);

Output:

[2, 4]

5. reduce()

Reduces array to a single value.

let nums = [1, 2, 3];
let sum = nums.reduce((acc, val) => acc + val, 0);
console.log(sum);

Output:

6. every()

Checks if all elements satisfy condition.

let nums = [2, 4, 6];
let allEven = nums.every(n => n % 2 === 0);
console.log(allEven);

Output:

true

7. some()

Checks if at least one element satisfies condition.

let nums = [1, 3, 4];
let hasEven = nums.some(n => n % 2 === 0);
console.log(hasEven);

Output:

true

8. Array.from()

Creates array from iterable.

let str = "hi";
let arr = Array.from(str);
console.log(arr);

Output:

['h', 'i']

9. keys()

Returns array indices.

let arr = ["a", "b"];
console.log([...arr.keys()]);

Output:

[0, 1]

10. Spread Operator (...)

Expands array elements.

let arr = [1, 2];
let newArr = [...arr, 3, 4];
console.log(newArr);

Output:

[1, 2, 3, 4]

Reference
W3Schools
https://www.w3schools.com/js/js_array_iteration.asp

Why JavaScript is Single-Threaded

Athithya Sivasankarar — Wed, 15 Apr 2026 04:32:20 +0000

JavaScript is one of the most popular programming languages used to build interactive websites. One important concept you will often hear is that JavaScript is single-threaded.

What Does Single-Threaded Mean?

A single-threaded language can execute only one task at a time.

JavaScript has:

One main thread
One call stack

This means tasks are executed one by one, in order.

Example:
console.log("Task 1");
console.log("Task 2");
console.log("Task 3");

Output:

Task 1
Task 2
Task 3

JavaScript does not run multiple lines at the same time.

Why is JavaScript Single-Threaded?

Designed for Web Browsers

JavaScript was originally created to run inside web browsers.

According to W3Schools:
JavaScript is used to control the behavior of web pages.

It works with the DOM (Document Object Model).

If JavaScript had multiple threads:

Two threads could try to change the same element at the same time
This could create confusion and errors

So, JavaScript is single-threaded to keep things simple and safe.

Easy to Learn and Use

Single-threaded design makes JavaScript:

Easier to understand
Easier to debug
Less complex

Developers don’t need to handle:

Thread management
Locks
Deadlocks

This is perfect for beginners.

Uses a Call Stack

JavaScript uses a call stack to manage execution.

Example:

function first() {
  console.log("First");
}

function second() {
  first();
  console.log("Second");
}

second();

Execution:

second() runs
first() runs
Then back to second()

Only one function runs at a time → single-threaded behavior

But JavaScript Can Handle Multiple Tasks

You might think:

“If JavaScript is single-threaded, how does it handle timers, APIs, etc.?”

Example:

console.log("Start");

setTimeout(() => {
  console.log("Hello after 2 seconds");
}, 2000);

console.log("End");

Output:

Start
End
Hello after 2 seconds

This happens because of the Event Loop

Event Loop

JavaScript uses:

Call Stack
Web APIs
Callback Queue
Event Loop

According to MDN Web Docs:
The event loop allows JavaScript to perform non-blocking operations even though it is single-threaded.

So JavaScript can:

Start a task
Continue other work
Come back later

JavaScript Basics

Athithya Sivasankarar — Fri, 10 Apr 2026 04:57:37 +0000

JavaScript is one of the most important programming languages used in web development.
It helps make websites interactive and dynamic.

we will understand:

What is JavaScript
Data Types in JavaScript
Difference between Primitive and Non-Primitive
Variables in JavaScript

1. What is JavaScript?

JavaScript is a versatile, dynamically typed programming language that brings life to web pages by making them interactive. It is used for building interactive web applications, supports both client-side and server-side development, and integrates seamlessly with HTML, CSS, and a rich standard library.

JavaScript is a single-threaded language that executes one task at a time.
It is an interpreted language which means it executes the code line by line.
The data type of the variable is decided at run-time in JavaScript, which is why it is called dynamically typed.

Example

<html>
<head></head>
<body>
    <h1>Check the console for the message!</h1>
    <script>
        console.log("Hello, World!");
    </script>
</body>
</html>

Output:

Hello World

2. Data Types in JavaScript

What is a Data Type?

A data type defines what kind of value a variable holds (number, text, etc.).

JavaScript is dynamically typed, meaning you don’t need to define the type manually.

Types of Data in JavaScript

According to W3Schools, JavaScript has 8 data types:

Primitive Data Types (7 types)

1. Number

let x = 10;

2. String

let name = "Athithya";

3. Boolean

let isStudent = true;

4. Undefined

let a;

5. Null

let value = null;

6. BigInt

let big = 12345678901234567890n;

7. Symbol

let id = Symbol("id");

These are called primitive because they store a single value.

Non-Primitive Data Type

Object

let person = {
  name: "Athithya",
  age: 21
};

Objects can store multiple values (key-value pairs).

Difference Between Primitive and Non-Primitive

Feature	Primitive	Non-Primitive
Type	Basic data	Complex data
Storage	Single value	Multiple values
Mutability	Immutable	Mutable
Examples	Number, String	Object, Array
Memory	Stored directly	Stored by reference

Example

// Primitive
let a = 10;
let b = a;
b = 20;

console.log(a); // 10

// Non-Primitive
let obj1 = {name: "A"};
let obj2 = obj1;
obj2.name = "B";

console.log(obj1.name); // B

Primitive → value is copied
Non-Primitive → reference is copied

3. Variables in JavaScript

What is a Variable?

A variable is a container used to store data values.

Ways to Declare Variables

1. var

var x = 10;

Old method
Function scoped

2. let

let y = 20;

Block scoped
Can be updated

3. const

const z = 30;

Cannot be reassigned
Must be initialized

Example

let name = "Athithya";
let age = 21;
const country = "India";

console.log(name, age, country);

Output:

Athithya 21 India

typeof Operator

You can check data type using:

let x = "Hello";
console.log(typeof x);

Output:

string

The typeof operator returns the type of a variable.

Reference

https://www.w3schools.com/js/

JavaScript Array Methods

Athithya Sivasankarar — Wed, 08 Apr 2026 16:12:26 +0000

Arrays in JavaScript are used to store multiple values in a single variable.
JavaScript provides many built-in methods to work with arrays easily.

What is an Array?

An array is a collection of values.

Example:

let fruits = ["apple", "banana", "mango"];
console.log(fruits);

Output:

["apple", "banana", "mango"]

Common Array Methods

1. push() → Add element at end

let fruits = ["apple", "banana"];
fruits.push("mango");

console.log(fruits);

Output:

["apple", "banana", "mango"]

2. pop() → Remove last element

let fruits = ["apple", "banana", "mango"];
fruits.pop();

console.log(fruits);

Output:

["apple", "banana"]

3. shift() → Remove first element

let fruits = ["apple", "banana", "mango"];
fruits.shift();

console.log(fruits);

Output:

["banana", "mango"]

4. unshift() → Add element at beginning

let fruits = ["banana", "mango"];
fruits.unshift("apple");

console.log(fruits);

Output:

["apple", "banana", "mango"]

5. length → Find array size

let fruits = ["apple", "banana", "mango"];
console.log(fruits.length);

Output:

6. includes() → Check value

let fruits = ["apple", "banana", "mango"];
console.log(fruits.includes("banana"));

Output:

true

7. indexOf() → Find position

let fruits = ["apple", "banana", "mango"];
console.log(fruits.indexOf("mango"));

Output:

8. join() → Convert to string

let fruits = ["apple", "banana", "mango"];
console.log(fruits.join(", "));

Output:

apple, banana, mango

9. slice() → Get part of array

let fruits = ["apple", "banana", "mango"];
console.log(fruits.slice(0, 2));

Output:

["apple", "banana"]

10. splice() → Add/Remove elements

let fruits = ["apple", "banana", "mango"];
fruits.splice(1, 1);

console.log(fruits);

Output:

["apple", "mango"]

Reference

W3Schools

Using Objects as Functions, Function Constructor & this Keyword in JavaScript

Athithya Sivasankarar — Tue, 07 Apr 2026 18:01:53 +0000

JavaScript is a flexible language where functions and objects work closely together.

Functions as objects
Function constructor
thiskeyword

1. Functions as Objects

In JavaScript, functions are special types of objects.

This means:

Functions can be stored inside objects
Functions can have properties

Example: Function inside Object

const user = {
    name: "Athithya",
    greet: function() {
        return "Hello " + this.name;
    }
};

console.log(user.greet());

Output:

Hello Athithya

Explanation

user → object
greet → function (method)
this.name → refers to object value

Functions Can Have Properties

function greet() {}

greet.msg = "Hello";

console.log(greet.msg);

Output:

Hello

So, functions behave like objects.

2. Function Constructor

What is it?

A constructor function is used to create multiple objects using new.

Example

function Student(name, age) {
    this.name = name;
    this.age = age;

    this.display = function() {
        return this.name + " " + this.age;
    };
}

let s1 = new Student("Ram", 20);
console.log(s1.display());

Output:

Ram 20

Explanation

Student → constructor function
this.name → assign value
new Student() → creates object

3. this Keyword

this refers to the current object.

Example

const user = {
    name: "Athithya",
    show: function() {
        console.log(this.name);
    }
};

user.show();

Output:

Athithya

Explanation

this.name → refers to object's name
Inside object → this = that object

Reference

Understanding JavaScript Objects Using CRUD Operations

Athithya Sivasankarar — Mon, 06 Apr 2026 10:50:53 +0000

Objects are one of the most important concepts in JavaScript.
They allow us to store data in key-value pairs.

What is an Object?

An object is a collection of properties where each property has a key and a value.

Example:

const user = {
    name: "Athithya",
    age: 20
};

console.log(user);

Output:

{ name: "Athithya", age: 20 }

CRUD Operations in JavaScript Objects

CRUD stands for:

Create
Read
Update
Delete

1. Create (Adding Data)

We can create an object or add new properties.

Example:

const user = {};

user.name = "Athithya";
user.age = 20;

console.log(user);

Output:

{ name: "Athithya", age: 20 }

2. Read (Access Data)

We can access object values using dot notation.

Example:

const user = {
    name: "Athithya",
    age: 20
};

console.log(user.name);

Output:

Athithya

3. Update (Modify Data)

We can change existing values.

Example:

const user = {
    name: "Athithya",
    age: 20
};

user.age = 21;

console.log(user.age);

Output:

4. Delete (Remove Data)

We can remove properties using the delete keyword.

Example:

const user = {
    name: "Athithya",
    age: 20
};

delete user.age;

console.log(user);

Output:

{ name: "Athithya" }

Reference

https://www.w3schools.com/js/js_objects.asp

Types of Functions in JavaScript

Athithya Sivasankarar — Sat, 04 Apr 2026 16:58:52 +0000

1. Function Declaration

This is the basic way to create a function.

Example:

function sayHello() {
    console.log("Hello");
}

sayHello();

Output:

Hello

2. Function Expression

A function expression is a function that is created and assigned to a variable (or used as a value).

Example:

const sayHello = function() {
    console.log("Hello");
};

sayHello();

Output:

Hello

3. Arrow Function (Lambda)

Short and modern way to write functions.

Example:

const sayHello = () => {
    console.log("Hello");
};

sayHello();

Output:

Hello

4. Anonymous Function

Function without a name.

Example:

const greet = function() {
  return "Hi there!";
};

console.log(greet());

Output:

Hi there!

5. Callback Function

A function passed inside another function.

Example:

function greet(name, fun) {
    fun(name);
}

greet("Ram", function(name) {
    console.log("Hello " + name);
});

Output:

Hello Ram

6. IIFE (Immediately Invoked Function)

Runs immediately after writing.

Example:

(function() {
    console.log("Run now");
})();

Output:

Run now

7. Constructor Function

Used to create objects.

Example:

function Person(name) {
    this.name = name;
}

let p1 = new Person("Ram");
console.log(p1.name);

Output:

Ram

8. Generator Function

Used to return values one by one.

Example:

function* num() {
    yield 1;
}

let n = num();
console.log(n.next().value);

Output:

Reference

https://www.geeksforgeeks.org/javascript/functions-in-javascript/

Understanding Functions in JavaScript

Athithya Sivasankarar — Fri, 03 Apr 2026 17:42:02 +0000

What is a Function?

A function is a block of code designed to perform a specific task.
Instead of writing the same code again and again, you can write it once inside a function and reuse it whenever needed.

Why Use Functions?

Functions are useful because they:

Reduce code repetition
Make code easier to understand
Help in organizing large programs
Allow reuse of logic

How to Create a Function

In JavaScript, you can create a function using the function keyword.

Example:
function greet() { console.log("Hello, welcome to JavaScript!"); }
How to Call a Function

To execute (run) a function, you simply call it by its name.

greet();

Output:
Hello, welcome to JavaScript!

Functions with Parameters

Functions can take inputs called parameters.

Example:
function greetUser(name) { console.log("Hello " + name); } greetUser("Athithya");

Output:
Hello Athithya

Functions with Return Value

A function can return a value using the return keyword.

Example:
function add(a, b) { return a + b; } let result = add(5, 3); console.log(result);

Output:
8

Reference:

[https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Functions]

Student Marks Analysis Using JavaScript(Flow diagram)

Athithya Sivasankarar — Fri, 03 Apr 2026 05:46:45 +0000

Student Marks Analysis Using JavaScript (While Loop)

Athithya Sivasankarar — Thu, 02 Apr 2026 09:01:31 +0000

Program Explanation: Student Marks Analysis in JavaScript

This program is designed to analyze student marks using JavaScript. It calculates the total marks, average, number of failed subjects, and finally assigns a grade based on performance.

Step 1: Initialize Variables
let mark = [20,35,90,85,70];
let i = 0;
let failcount = 0;
let avg = 0;
let total = 0;
mark[] → Array storing marks of 5 subjects
i → Loop counter
failcount → Counts subjects where marks are less than 35
total → Stores sum of all marks
avg → Stores average marks

Step 2: Loop Through Marks
while(i < 5)
{
if(mark[i] < 35)
{
failcount++;
}
total = mark[i] + total;
i++;
}
The while loop runs from index 0 to 4
For each subject:
If marks are less than 35 → student failed in that subject
Add marks to total

Step 3: Display Total and Fail Count
console.log("fail count ->" + failcount);
console.log("Total ->" + total);
Prints number of failed subjects
Prints total marks

Step 4: Calculate Average
avg = Math.floor(total / 5);
console.log("Average ->" + avg);
Average is calculated by dividing total by number of subjects
Math.floor() removes decimal values (rounds down)

Step 5: Grade Calculation Logic
if(failcount > 0)
{
console.log("no grade");
}
If the student fails in any subject → No grade is assigned
If No Failures, Assign Grade:
else if(avg >= 90)
{
console.log("Grade A");
}
else if(avg >= 80)
{
console.log("Grade B");
}
else if(avg >= 70)
{
console.log("Grade C");
}
else if(avg >= 60)
{
console.log("Grade D");
}
else if(avg >= 50)
{
console.log("Grade E");
}
else
{
console.log("No Grade");
}
Grade is assigned based on average marks:
90+ → Grade A
80–89 → Grade B
70–79 → Grade C
60–69 → Grade D
50–59 → Grade E
Below 50 → No Grade

Final Output (For Given Input)
fail count -> 1

Total -> 300

Average -> 60

no grade

Program:

Output:
fail count ->0
Total ->357
Average ->71
Grade C

=== Code Execution Successful ===

Multiples of 3 and Multiples of 5 javascript program

Athithya Sivasankarar — Sat, 28 Mar 2026 09:22:06 +0000

Looping Programs – Flowcharts

Athithya Sivasankarar — Fri, 27 Mar 2026 08:47:07 +0000

Multiples of 3 AND 5 &
Multiples of 3 OR 5
Divisors of Given Number &
Count of Divisors

Count of Digits &
Sum of Digits