DEV Community: Kavitha

Array Iteration Methods in JavaScript

Kavitha — Sat, 18 Apr 2026 14:08:33 +0000

When working with arrays in JavaScript, you don’t always need traditional loops like for or while. JavaScript provides built-in array iteration methods that make your code cleaner, shorter, and easier to understand.
These methods internally loop through the array and apply a function to each element.

1. `forEach()` – Perform an action on each element

forEach() is used when you want to execute a function for every element in the array.

let numbers = [1, 2, 3];

numbers.forEach((num, index) => {
    console.log(num, index);
});

Key points:

Does not return a new array
Used for side effects (printing, updating values, etc.)

2. `map()` – Transform each element

map() creates a new array by applying a function to each element.

let numbers = [1, 2, 3];

let squared = numbers.map(num => num * num);

console.log(squared); // [1, 4, 9]

Key points:

Returns a new array
Does not modify the original array

3. `filter()` – Select elements based on condition

filter() returns a new array with elements that satisfy a condition.

let numbers = [1, 2, 3, 4, 5];

let evenNumbers = numbers.filter(num => num % 2 === 0);

console.log(evenNumbers); // [2, 4]

Key points:

Returns a new array
Useful for extracting specific data

4. `reduce()` – Reduce array to a single value

reduce() processes all elements and returns a single output value.

let numbers = [1, 2, 3, 4];

let sum = numbers.reduce((acc, curr) => acc + curr, 0);

console.log(sum); // 10

Key points:

Takes an accumulator (acc) and current value (curr)
Can be used for sum, product, or complex calculations

5. `find()` – Get the first matching element

find() returns the first element that satisfies a condition.

let numbers = [10, 20, 30];

let result = numbers.find(num => num > 15);

console.log(result); // 20

Key points:

Returns only one value
Stops once condition is met

6. `some()` – Check if at least one element matches

let numbers = [1, 3, 5];

let hasEven = numbers.some(num => num % 2 === 0);

console.log(hasEven); // false

Key points:

Returns true or false
Stops early when condition is satisfied

7. `every()` – Check if all elements match

let numbers = [2, 4, 6];

let allEven = numbers.every(num => num % 2 === 0);

console.log(allEven); // true

Key points:

Returns true only if all elements satisfy condition

8. `flatMap()` – Map + Flatten

This method first maps each element and then flattens the result by one level.

let arr = [1, 2, 3];

let result = arr.flatMap(num => [num, num * 2]);

console.log(result); // [1, 2, 2, 4, 3, 6]

Why use it?

Avoids nested arrays
Combines map() + flat() in one step ([DEV Community][1])

9. `reduceRight()` – Reduce from Right to Left

Works like reduce() but processes elements from the end.

let arr = ["a", "b", "c"];

let result = arr.reduceRight((acc, val) => acc + val);

console.log(result); // "cba"

Use case:

Reverse operations
Right-to-left calculations ([DEV Community][1])

10. `Array.from()` – Convert to Array

Creates a new array from iterable objects like strings.

let str = "hello";

let arr = Array.from(str);

console.log(arr); // ["h", "e", "l", "l", "o"]

Use case:

Convert strings, sets, or node lists into arrays ([DEV Community][1])

11. `keys()` – Get Index Iterator

Returns an iterator of array indices.

let arr = ["a", "b"];

for (let key of arr.keys()) {
    console.log(key);
}

Output:

0
1

12. `entries()` – Get Index + Value

Returns both index and value as pairs.

let arr = ["a", "b"];

for (let [index, value] of arr.entries()) {
    console.log(index, value);
}

13. `values()` – Get Values Iterator

Returns only values (similar to for...of).

let arr = ["a", "b"];

for (let value of arr.values()) {
    console.log(value);
}

Note: These iterator methods (keys, values, entries) return iterator objects that help traverse arrays efficiently ([DEV Community][2])

14. `with()` – Replace Value (Non-Mutating)

Creates a new array with one value replaced.

let arr = [1, 2, 3];

let newArr = arr.with(1, 100);

console.log(newArr); // [1, 100, 3]

Key point:

Does NOT modify original array ([DEV Community][1])

15. Spread Operator (`...`) – Expand Array

let arr1 = [1, 2];
let arr2 = [3, 4];

let result = [...arr1, ...arr2];

console.log(result); // [1, 2, 3, 4]

Use case:

Copy arrays
Merge arrays ([DEV Community][1])

16. Rest Operator (`...`) – Collect Values

function sum(...nums) {
    return nums.reduce((a, b) => a + b);
}

console.log(sum(1, 2, 3)); // 6

Use case:

Handle variable number of arguments

Conclusion

Array iteration methods are essential for writing modern JavaScript. They reduce complexity and make your code more readable compared to traditional loops.

Callback Functions in JavaScript

Kavitha — Thu, 16 Apr 2026 13:29:03 +0000

Callback Functions in JavaScript

JavaScript is a powerful programming language that supports functions as first-class citizens. This means functions can be stored in variables, passed as arguments, and returned from other functions. One important concept based on this is the callback function.

What is a Callback Function?

A callback function is a function that is passed as an argument to another function and is executed later.
In simple words, one function “calls back” another function after completing its task.

Syntax

function mainFunction(callback) {
    callback();
}

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

mainFunction(sayHello);

Output

Hello

Here:

sayHello is the callback function
mainFunction is the function that receives and executes it

Why Do We Use Callback Functions?

Callbacks are mainly used for:

Reusing code
Performing actions after another task finishes
Handling asynchronous operations
Event handling

Example 1: Simple Callback

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

function message() {
    console.log("Welcome to JavaScript");
}

greet("Kavitha", message);

Output

Hello Kavitha
Welcome to JavaScript

Here, after greeting the user, the message() function is called.

Example 2: Callback with Calculation

function add(a, b, callback) {
    let result = a + b;
    callback(result);
}

function display(result) {
    console.log("Sum is: " + result);
}

add(10, 20, display);

Output

Sum is: 30

The result is passed to another function using a callback.

Example 3: Callback with `setTimeout()`

This is one of the most common examples.

console.log("Start");

setTimeout(function () {
    console.log("This runs after 2 seconds");
}, 2000);

console.log("End");

Output

Start
End
This runs after 2 seconds

Even though the timeout function is written in the middle, it executes later.

This happens because JavaScript handles it asynchronously.

Real-Time Use of Callback Functions

Callbacks are used in:

Button click events
API responses
Timers
Array methods like forEach(), map(), filter()

Example: `forEach()`

let numbers = [1, 2, 3];

numbers.forEach(function(num) {
    console.log(num);
});

Here, the function inside forEach() is a callback.

Important Note

When passing a callback, do not use parentheses.

Correct:

mainFunction(sayHello);

Wrong:

mainFunction(sayHello());

Because sayHello() executes immediately.

Conclusion

Callback functions are an essential concept in JavaScript. They help make code more flexible and are widely used in asynchronous programming and event handling.

Arrays in JavaScript

Kavitha — Tue, 14 Apr 2026 12:58:38 +0000

Arrays are one of the most commonly used data structures in JavaScript.
They allow us to store multiple values in a single variable, making code cleaner and easier to manage.
Instead of creating many variables, arrays help group related values together.

For example, rather than writing:

let mark1 = 85;
let mark2 = 90;
let mark3 = 78;

we can write:

let marks = [85, 90, 78];

This makes the code more organized and scalable.

What is an Array?

An array is a special type of object in JavaScript used to store an ordered collection of values.

let fruits = ["apple", "banana", "orange"];

Here:

"apple" is at index 0
"banana" is at index 1
"orange" is at index 2

JavaScript arrays always start indexing from 0.

Accessing Array Elements

You can access elements using their index.

let fruits = ["apple", "banana", "orange"];

console.log(fruits[0]);
console.log(fruits[1]);

Output:

apple
banana

Updating Values

You can modify any value in the array.

let numbers = [10, 20, 30];

numbers[1] = 50;

console.log(numbers);

Output:

[10, 50, 30]

Array Length

To find the number of elements in an array, use .length.

let colors = ["red", "blue", "green"];

console.log(colors.length);

Output:

Looping Through Arrays

Arrays are commonly used with loops.

let nums = [1, 2, 3, 4, 5];

for (let i = 0; i < nums.length; i++) {
    console.log(nums[i]);
}

This prints each element one by one.

Important Built-in Array Methods(To be discussed)

`push()` – Add element at the end

let arr = [1, 2, 3];
arr.push(4);

console.log(arr);

Output:

[1, 2, 3, 4]

`pop()` – Remove last element

arr.pop();

`shift()` – Remove first element

arr.shift();

`unshift()` – Add element at the beginning

arr.unshift(0);

Arrays Can Store Multiple Data Types

JavaScript arrays can hold different types of values.

let mixed = [10, "hello", true, 25.5];

This flexibility is one of JavaScript’s strengths.

Is Array a Data Type?

Arrays are technically objects in JavaScript.

typeof [1, 2, 3]

Output:

"object"

To specifically check for arrays:

Array.isArray([1, 2, 3]);

Output:

true

Conclusion

Arrays are essential in JavaScript programming.
They help manage collections of data efficiently and are widely used in web development, data handling, and algorithms.

Objects in JS

Kavitha — Thu, 09 Apr 2026 23:49:15 +0000

1) What is an Object?

An object stores data in key : value pairs.

Syntax

let mobile = {
    brand: "Vivo",
    model: "V70",
    price: 25000
};

Here,

brand → key
"Vivo" → value

Accessing Object Values

console.log(mobile.brand);
console.log(mobile.model);

Output

Vivo
V70

Real-World Example

let student = {
    name: "Kavitha",
    age: 20,
    department: "EEE"
};

console.log(student.name);

Output:

Kavitha

2) Creating Object Inside an Object

This is called a nested object.

It means one object is stored inside another object.

Example: Mobile Object

let mobile = {
    name: "Vivo",
    model: "V70",

    camera: {
        rear: "32MP",
        front: "64MP"
    }
};

Here camera itself is another object.

Access Nested Object

console.log(mobile.camera.rear);
console.log(mobile.camera.front);

Output

32MP
64MP

Real-World Understanding

Think like this:

A student has an address

Address itself has:

city
state
pincode

So:

let student = {
    name: "Kavitha",

    address: {
        city: "Tirunelveli",
        state: "Tamil Nadu",
        pincode: 627001
    }
};

Access:

console.log(student.address.city);

Output:

Tirunelveli

3) Creating Function Inside an Object

When a function is created inside an object, it is called a method.
Methods represent actions.

Example

let mobile = {
    name: "Vivo",

    call: function() {
        console.log("Calling...");
    }
};

Calling the Function

mobile.call();

Output:

Calling...

Short Modern Syntax

This is the cleaner way:

let mobile = {
    name: "Vivo",

    call() {
        console.log("Calling...");
    }
};

This is commonly used.

4) Object + Nested Object + Function Together

This is the complete structure

let mobile = {
    name: "Vivo",
    model: "V70",

    camera: {
        rear: "32MP",
        front: "64MP"
    },

    display: {
        size: "6.8 inch",
        type: "AMOLED"
    },

    calling() {
        console.log("Calling Amma...");
    },

    browsing() {
        console.log("Browsing...");
    }
};

Access Everything

console.log(mobile.name);
console.log(mobile.camera.front);
console.log(mobile.display.size);

mobile.calling();
mobile.browsing();

Output

Vivo
64MP
6.8 inch
Calling Amma...
Browsing...

Why Do We Use This?

This is heavily used in:

JavaScript projects
React
APIs
JSON data
backend responses
real-world applications

Example:

user.profile.name
product.details.price
robot.sensor.temperature

Simple Memory Trick

Object = thing

Nested object = thing inside thing

Function inside object = action of that thing

Example:

Car → object
Engine → object inside object
Start → function inside object

Looping Programs JS(Part 2)

Kavitha — Thu, 09 Apr 2026 14:46:08 +0000

18. Addition of first n numbers
Program:

<!DOCTYPE html>
<html>
<head>
    <title>document</title>
</head>
<body>
    <script>
        let n=50;
        let sum=0;
        for(let i=1;i<=n;i++){
            sum+=i;
        }
        document.write("Sum: "+sum);
    </script>
</body>
</html>

19.Factorial
Program:

<!DOCTYPE html>
<html>
<head>
    <title>document</title>
</head>
<body>
    <script>
        let n=5;
        let fact=1;
        for(let i=1;i<=n;i++){
            fact=fact*i;
        }
        document.write(fact);
    </script>
</body>
</html>

20.Greatest Common Divisor
Program:

<!DOCTYPE html>
<html>
<head>
    <title>document</title>
</head>
<body>
    <script>
        let n1=2;
        let n2=4;
        while(n2!==0){
            let temp=n2;
            n2=n1%n2;
            n1=temp;
        }
        document.write("GCD:"+n1);

    </script>
</body>
</html>

21.Least Common Multiple
Program:

<!DOCTYPE html>
<html>
<head>
    <title>document</title>
</head>
<body>
    <script>
        let n1 = 2;
        let n2 = 4;

        let a = n1;
        let b = n2;

        while (n2 !== 0) {
            let temp = n2;
            n2 = n1 % n2;
            n1 = temp;
        }

        let gcd = n1;

        let lcm = (a * b) / gcd;

        document.write("LCM = " + lcm);
    </script>
</body>
</html>

22. `2^5`

console.log(Math.pow(2, 5)); // Output: 32

23. Decimal to Binary

let decimal = 23;
let binary = decimal.toString(2);
console.log(binary); // Output: 10111

24. Binary to Decimal

let binaryNum = "10111";
let decimalNum = parseInt(binaryNum, 2);
console.log(decimalNum); // Output: 23

25. Fibonacci Series

let n = 10;
let a = 0, b = 1;
console.log(a);
console.log(b);
for (let i = 2; i < n; i++) {
    let c = a + b;
    console.log(c);
    a = b;
    b = c;
}

26. Swapping Two Numbers

let x = 5, y = 10;
let temp = x;
x = y;
y = temp;
console.log(x, y); // Output: 10 5

27. Swapping Without Third Variable

let a = 5, b = 10;
a = a + b;
b = a - b;
a = a - b;
console.log(a, b); // Output: 10 5

28. Fibonacci Without Third Variable

let n1 = 0, n2 = 1;
console.log(n1);
console.log(n2);
for (let i = 2; i < 10; i++) {
    n2 = n1 + n2;
    n1 = n2 - n1;
    console.log(n2);
}

29. Odd Positions & Even Positions

let arr = [1,2,3,4,5,6,7,8,9,10];
let odd = [], even = [];
for (let i = 0; i < arr.length; i++) {
    if (i % 2 === 0) even.push(arr[i]);
    else odd.push(arr[i]);
}
console.log("Even Positions:", even);
console.log("Odd Positions:", odd);

30. First 10 Prime Numbers

let primes = [];
for (let i = 2; primes.length < 10; i++) {
    let isPrime = true;
    for (let j = 2; j <= Math.sqrt(i); j++) {
        if (i % j === 0) isPrime = false;
    }
    if (isPrime) primes.push(i);
}
console.log(primes);

31. Sum of Digits Until Single Digit

let num = 9876;
while (num > 9) {
    let sum = 0;
    num.toString().split('').forEach(d => sum += Number(d));
    num = sum;
}
console.log(num);

32. Printing 5! 4! 3! 2! 1!

function factorial(n) {
    return n <= 1 ? 1 : n * factorial(n-1);
}
for (let i = 5; i >= 1; i--) {
    console.log(factorial(i));
}

33. Printing 110 29 38 47

for (let i = 1, j = 10; i <= 4; i++, j--) {
    console.log(i * j);
}

34. Printing 1 11 121

for (let i = 0; i < 3; i++) {
    console.log(Math.pow(11, i));
}

35. Printing 1 8 27 64

for (let i = 1; i <= 4; i++) {
    console.log(Math.pow(i, 3));
}

36. Printing 1 4 9 16 … 100

for (let i = 1; i <= 10; i++) {
    console.log(i * i);
}

37. Printing 1 4 27 256

let powers = [1,2,3,4];
for (let i = 0; i < powers.length; i++) {
    console.log(Math.pow(powers[i], powers[i]));
}

38. Square Root of a Number

let nSqrt = 64;
console.log(Math.sqrt(nSqrt)); // Output: 8

39. Spy Number

A Spy number is one where sum of digits = product of digits.

let spyNum = 1124;
let sum = 0, product = 1;
spyNum.toString().split('').forEach(d => {
    let num = Number(d);
    sum += num;
    product *= num;
});
console.log(sum === product ? "Spy Number" : "Not Spy Number");

40. Prime Numbers in Fibonacci Series

let fib = [0,1];
for (let i = 2; i < 10; i++) {
    fib[i] = fib[i-1] + fib[i-2];
}
let primesInFib = fib.filter(n => {
    if (n < 2) return false;
    for (let i = 2; i <= Math.sqrt(n); i++) {
        if (n % i === 0) return false;
    }
    return true;
});
console.log(primesInFib);

Functions in JavaScript: A Clear Guide

Kavitha — Thu, 09 Apr 2026 14:29:04 +0000

Functions in JavaScript

Functions are one of the most important building blocks in JavaScript. They allow you to organize code into reusable blocks that perform a specific task. Understanding functions well will make your code cleaner, easier to maintain, and more efficient.

1. What is a Function?

A function is a block of code designed to perform a particular task. Instead of writing the same code multiple times, you can define a function once and call it whenever needed.

Syntax:

function functionName(parameters) {
    // Code to execute
    return value; // optional
}

Example:

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

greet("Kavitha"); // Output: Hello, Kavitha!

2. Components of a Function

Function Name – The identifier used to call the function.
Parameters – Input values passed to the function (optional).
Function Body – The code block that runs when the function is called.
Return Statement – Sends a value back to the caller (optional).

Example:

function add(a, b) {
    return a + b; // Returns the sum of a and b
}

let result = add(5, 3);
console.log(result); // Output: 8

3. Types of Functions

a) Function Declaration

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

Hoisted in JavaScript → Can be called before declaration.
Classic way of defining functions.

b) Function Expression

const multiply = function(x, y) {
    return x * y;
};
console.log(multiply(4, 5)); // Output: 20

Not hoisted → Must be defined before calling.
Can be anonymous or named.

c) Arrow Functions

const divide = (a, b) => a / b;
console.log(divide(10, 2)); // Output: 5

Shorter syntax.
No this binding → Useful in modern JS like React or Node.js.

4. Functions with Default Parameters

You can set default values for parameters in case no value is passed:

function greet(name = "Guest") {
    console.log("Hello, " + name + "!");
}

greet();         // Output: Hello, Guest!
greet("Kavitha"); // Output: Hello, Kavitha!

5. Functions Returning Values

A function can return a value to be used elsewhere:

function square(number) {
    return number * number;
}

let result = square(6);
console.log(result); // Output: 36

6. Why Use Functions?

Reusability: Write once, use multiple times.
Maintainability: Easy to update logic in one place.
Modularity: Break code into smaller, manageable parts.
Readability: Makes code cleaner and easier to understand.

7. Best Practices

Give functions meaningful names: calculateSum instead of doStuff.
Keep functions small and focused on one task.
Avoid side effects when possible → Functions should ideally only use inputs and return outputs.
Use arrow functions for concise syntax when appropriate.

Looping Programs using Java(part 1)

Kavitha — Sat, 04 Apr 2026 17:04:03 +0000

1) Print `1 1 1 1 1`

This program prints number 1 five times.

public class Main {
    public static void main(String[] args) {
        for(int i = 1; i <= 5; i++) {
            System.out.print("1 ");
        }
    }
}

Output

1 1 1 1 1

2) Print `1 2 3 4 5`

public class Main {
    public static void main(String[] args) {
        for(int i = 1; i <= 5; i++) {
            System.out.print(i + " ");
        }
    }
}

Output

1 2 3 4 5

3) Print `1 3 5 7 9`

Odd numbers can be printed by increasing by 2.

public class Main {
    public static void main(String[] args) {
        for(int i = 1; i <= 9; i += 2) {
            System.out.print(i + " ");
        }
    }
}

Output

1 3 5 7 9

4) Print `3 6 9 12 15`

Multiples of 3.

public class Main {
    public static void main(String[] args) {
        for(int i = 3; i <= 15; i += 3) {
            System.out.print(i + " ");
        }
    }
}

Output

3 6 9 12 15

5) Multiples of 3 and 5

Numbers divisible by both 3 and 5.

public class Main {
    public static void main(String[] args) {
        for(int i = 1; i <= 50; i++) {
            if(i % 3 == 0 && i % 5 == 0) {
                System.out.print(i + " ");
            }
        }
    }
}

6) Multiples of 3 or 5

Numbers divisible by either 3 or 5.

public class Main {
    public static void main(String[] args) {
        for(int i = 1; i <= 50; i++) {
            if(i % 3 == 0 || i % 5 == 0) {
                System.out.print(i + " ");
            }
        }
    }
}

7) Divisors of a Given Number

Example: divisors of 12 → 1 2 3 4 6 12

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int num = sc.nextInt();

        for(int i = 1; i <= num; i++) {
            if(num % i == 0) {
                System.out.print(i + " ");
            }
        }
    }
}

8) Count of Divisors

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int num = sc.nextInt();
        int count = 0;

        for(int i = 1; i <= num; i++) {
            if(num % i == 0) {
                count++;
            }
        }

        System.out.println("Count = " + count);
    }
}

9) Prime Number

A prime number has exactly 2 divisors.

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int num = sc.nextInt();
        int count = 0;

        for(int i = 1; i <= num; i++) {
            if(num % i == 0) {
                count++;
            }
        }

        if(count == 2)
            System.out.println("Prime");
        else
            System.out.println("Not Prime");
    }
}

10) Reverse Printing a Number

Example: 12345 → 5 4 3 2 1

public class Main {
    public static void main(String[] args) {
        int num = 12345;

        while(num > 0) {
            int digit = num % 10;
            System.out.print(digit + " ");
            num = num / 10;
        }
    }
}

11) Count of Digits

public class Main {
    public static void main(String[] args) {
        int num = 12345;
        int count = 0;

        while(num > 0) {
            count++;
            num = num / 10;
        }

        System.out.println(count);
    }
}

12) Sum of Digits

Example: 123 → 1+2+3 = 6

public class Main {
    public static void main(String[] args) {
        int num = 123;
        int sum = 0;

        while(num > 0) {
            sum += num % 10;
            num = num / 10;
        }

        System.out.println(sum);
    }
}

13) Reverse the Number

Example: 123 → 321

public class Main {
    public static void main(String[] args) {
        int num = 123;
        int rev = 0;

        while(num > 0) {
            rev = rev * 10 + num % 10;
            num = num / 10;
        }

        System.out.println(rev);
    }
}

14) Palindrome Number

A number is palindrome if reverse equals original.

Example: 121

public class Main {
    public static void main(String[] args) {
        int num = 121;
        int original = num;
        int rev = 0;

        while(num > 0) {
            rev = rev * 10 + num % 10;
            num = num / 10;
        }

        if(original == rev)
            System.out.println("Palindrome");
        else
            System.out.println("Not Palindrome");
    }
}

15) Armstrong Number

Example: 153

1³ + 5³ + 3³ = 153

public class Main {
    public static void main(String[] args) {
        int num = 153;
        int original = num;
        int sum = 0;

        while(num > 0) {
            int digit = num % 10;
            sum += digit * digit * digit;
            num = num / 10;
        }

        if(original == sum)
            System.out.println("Armstrong");
        else
            System.out.println("Not Armstrong");
    }
}

16) Neon Number

Example: 9

9² = 81

8 + 1 = 9

public class Main {
    public static void main(String[] args) {
        int num = 9;
        int square = num * num;
        int sum = 0;

        while(square > 0) {
            sum += square % 10;
            square = square / 10;
        }

        if(sum == num)
            System.out.println("Neon Number");
        else
            System.out.println("Not Neon Number");
    }
}

17) Strong Number

Example: 145

1! + 4! + 5! = 145

public class Main {
    public static void main(String[] args) {
        int num = 145;
        int original = num;
        int sum = 0;

        while(num > 0) {
            int digit = num % 10;
            int fact = 1;

            for(int i = 1; i <= digit; i++) {
                fact *= i;
            }

            sum += fact;
            num = num / 10;
        }

        if(sum == original)
            System.out.println("Strong Number");
        else
            System.out.println("Not Strong Number");
    }
}

Looping Programs-JS(Part1)

Kavitha — Sat, 04 Apr 2026 06:32:44 +0000

1.Multiples of 3 and 5

Program:

<!DOCTYPE html>
<html>
    <head>
    <title>document</title>
    </head>
    <body>
        <script>

        for(let i=1;i<=30;i++){
            if(i%3===0 && i%5===0){
                document.write("Multiples of 3 and 5:"+i+ "<br>");
            }
        }
</script>
    </body>
</html>

Output:

Multiples of 3 and 5:15
Multiples of 3 and 5:30

2.Multiples of 3 or 5

Program:

<!DOCTYPE html>
<html>
    <head>
    <title>document</title>
    </head>
    <body>
        <script>

        for(let i=1;i<=30;i++){
            if(i%3===0 || i%5===0){
                document.write(i+"<br>");
            }
        }
</script>
    </body>
</html>

Output:

3.Divisors of given number
Program:

<!DOCTYPE html>
<html>
    <head>
    <title>document</title>
    </head>
    <body>
        <script>

        let num=6;
        for(let i=1;i<=num;i++){
            if(num%i==0){
                document.write(i+" ");
            }
        }
</script>
    </body>
</html>

Output:

1 2 3 6

4.Count of Divisors of given number
Program:

<!DOCTYPE html>
<html>
    <head>
    <title>document</title>
    </head>
    <body>
        <script>

        let num=20;
        let count=0;
        for(let i=1;i<=num;i++){
            if(num%i==0){
                document.write(i+" ");

                count++
            }

        }
        document.write("<br>");
        document.write("Count:"+count);
</script>
    </body>
</html>

Output:

1 2 4 5 10 20
Count:6

5.Prime Number
i)Finding whether the given number is prime or not:
Program:

<!DOCTYPE html>
<html>
    <head>
    <title>document</title>
    </head>
    <body>
        <script>

        let num=7;
        let count=0;
        for(let i=1;i<=num;i++){
            if(num%i===0){
                count++;
            }
        }
        if(count===2){
            document.write(num +" is a prime number");
        }
        else{
            document.write(num +" is not  a prime number");
        }
</script>
    </body>
</html>

Output:

7 is a prime number

ii)Printing all the prime numbers within the given limit:

Program:

<!DOCTYPE html>
<html>
<head>
    <title>document</title>
</head>
<body>
    <script>
        let limit = 20;
        for (let num = 2; num <= limit; num++) {
            let count = 0;

            for (let i = 1; i <= num; i++) {
                if (num % i === 0) {
                    count++;
                }
            }

            if (count === 2) {
                document.write(num + "<br>");
            }
        }
    </script>
</body>
</html>

Output:

6.Reverse Printing a number
Program:

<!DOCTYPE html>
<html>
    <head>
    <title>document</title>
    </head>
    <body>
        <script>

        let num=1234;
        let reverse=0;
        while(num>0){
            let digit=num%10;
            reverse=reverse*10+digit;
            num=Math.floor(num/10);
        }
        document.write("Reverse: "+reverse);

</script>
    </body>
</html>

Output:

Reverse: 4321

7.Count of Digits
Program:

<!DOCTYPE html>
<html>
    <head>
    <title>document</title>
    </head>
    <body>
        <script>

        let num=1234;
        let count=0;
        while(num>0){
            let digit=num%10;
            num=Math.floor(num/10);
            count++;
        }
        document.write("Count of digits: "+count);

</script>
    </body>
</html>

Output:

Count of digits: 4

8.Sum of Digits
Program:

<!DOCTYPE html>
<html>
    <head>
    <title>document</title>
    </head>
    <body>
        <script>

        let num=5555;
        let sum=0;
        while(num>0){
            let digit=num%10;
            sum+=digit;
            num=Math.floor(num/10);

        }
        document.write("Sum of the digits: "+sum);

</script>
    </body>
</html>

Output:

Sum of the digits: 20

9.Palindrome
Program

<!DOCTYPE html>
<html>
<head>
    <title>document</title>
</head>
<body>
    <script>
        let num=121;
        let reverse=0;
        let n=num;
        while(num>0){
            let digit=num%10;
            reverse=reverse*10+digit;
            num=Math.floor(num/10);
        }
        if(n===reverse){
            document.write(n+" is a palindrome number");
        }
        else{
            document.write(n+" is not a palindrome number");
        }
    </script>
</body>
</html>

Output:

121 is a palindrome number

10.Armstrong Number
Program

<!DOCTYPE html>
<html>
<head>
    <title>document</title>
</head>
<body>
    <script>
        let num=153;
        let sum=0;
        let n=num;
        while(num>0){
            let digit=num%10;
            sum=sum+digit**3;
            num=Math.floor(num/10);
        }
        if(n===sum){
            document.write(n+" is a armstrong number");
        }
        else{
            document.write(n+" is not a armstrong  number");
        }
    </script>
</body>
</html>

Output:

153 is a armstrong number

11.Neon Number
Program

<!DOCTYPE html>
<html>
<head>
    <title>document</title>
</head>
<body>
    <script>
        let num=1;
        let square=num*num;
        let sum=0;
        while (square>0){
            let digit=square%10;
            sum +=digit;
            square=Math.floor(square/10);

        }
        if(num===sum){
            document.write(num+" is a neon number");
        }
        else{
            document.write(num+" is not a neon  number");
        }
    </script>
</body>
</html>

Output:

1 is a neon number

12.Strong Number
Program:

<!DOCTYPE html>
<html>
<head>
    <title>document</title>
</head>
<body>
    <script>
        let num = 145;
        let n = num;
        let sum = 0;

        while (num > 0) {
            let digit = num % 10;
            let fact = 1;

            for (let i = 1; i <= digit; i++) {
                fact = fact * i;
            }

            sum = sum + fact;
            num = Math.floor(num / 10);
        }

        if (sum === n) {
            document.write(n + " is a Strong Number");
        } 
      else {
            document.write(n + " is Not a Strong Number");
        }
    </script>
</body>
</html>

Output:

145 is a Strong Number

Looping Statements in JS

Kavitha — Sat, 04 Apr 2026 05:19:02 +0000

Looping Statements in JavaScript

Looping statements in JavaScript are used to repeat a block of code multiple times until a condition becomes false. Instead of writing the same code again and again, loops help make the code shorter and easier to manage.

JavaScript mainly provides the following loops:

1) `for` Loop

The for loop is used when we know how many times the loop should run.

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

Output:

Here, the loop starts from 1 and runs until 5.

2) `while` Loop

The while loop runs as long as the given condition is true.

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

This also prints numbers from 1 to 5.

Example Programs:

Looping Programs in JavaScript

1) `1 1 1 1 1`

Print the number 1 five times.

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

Output:

2) `1 2 3 4 5`

Print numbers from 1 to 5.

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

Output:

3) `1 3 5 7 9`

Print the first five odd numbers.

for (let i = 1; i <= 9; i += 2) {
    console.log(i);
}

Output:

4) `3 6 9 12 15`

Print multiples of 3.

for (let i = 3; i <= 15; i += 3) {
    console.log(i);
}

Output:

Conclusion

Loops are very useful in JavaScript for performing repetitive tasks such as printing numbers, iterating through arrays, and processing data efficiently.

Scenario Based Questions-Conditional Statements(JS)

Kavitha — Tue, 31 Mar 2026 16:59:58 +0000

1) Shopping Discount System

In online shopping websites, discounts are applied based on the purchase amount.

Rules

Amount ≥ 5000 → 20% discount
Amount ≥ 2000 → 10% discount
Otherwise → No discount
Members get an extra 10% discount

Program

<!DOCTYPE html>
<html>
<head>
    <title>Shopping Discount</title>
</head>
<body>
<script>
    let amount = 5000;
    let isMember = true;
    let discount = 0;

    if (amount >= 5000) {
        discount = 20;
    }
    else if (amount >= 2000) {
        discount = 10;
    }
    else {
        discount = 0;
    }

    if (isMember) {
        discount = discount + 10;
    }

    let finalPrice = amount - (amount * discount / 100);

    document.write("Final Price: " + finalPrice);
</script>
</body>
</html>

Output

Final Price: 3500

Explanation

Initial discount = 20%
Member discount = 10%
Total discount = 30%
Final price = 5000 - 1500 = 3500

2) Login Access Check

This is a basic login validation system.

Rules

Allow login only if:

Username = "admin"
Password = "1234"
User is not blocked

Program

<!DOCTYPE html>
<html>
<head>
    <title>Login Check</title>
</head>
<body>
<script>
    let username = "kavitha";
    let password = "1234";
    let isBlocked = false;

    if (username == "admin") {
        if (password == "1234") {
            if (!isBlocked) {
                console.log("User verified");
            }
            else {
                console.log("User blocked");
            }
        }
        else {
            console.log("Incorrect password");
        }
    }
    else {
        console.log("Incorrect username");
    }
</script>
</body>
</html>

Output

Incorrect username

Explanation

Since username is "kavitha" and not "admin", it prints:

Incorrect username

3) Traffic Signal System

A simple real-time example using traffic signal colors.

Rules

Red → Stop
Yellow → Get Ready
Green → Go

Program

<!DOCTYPE html>
<html>
<head>
    <title>Traffic Signal</title>
</head>
<body>
<script>
    let color = "red";

    if (color == "red") {
        document.write("STOP!");
    }
    else if (color == "yellow") {
        document.write("GET READY!");
    }
    else {
        document.write("GO!");
    }
</script>
</body>
</html>

Output

STOP!

4) ATM Withdrawal System

This program checks whether the withdrawal is valid.

Rules

If amount > balance → Insufficient funds
If amount ≤ 0 → Invalid amount
Otherwise deduct amount

Program

<!DOCTYPE html>
<html>
<head>
    <title>ATM Withdrawal</title>
</head>
<body>
<script>
    let balance = 5000;
    let withdrawalAmount = 500;

    if (withdrawalAmount > balance) {
        document.write("Insufficient funds");
    }
    else if (withdrawalAmount <= 0) {
        document.write("Invalid amount");
    }
    else {
        let remaining = balance - withdrawalAmount;
        document.write("Remaining Balance: " + remaining);
    }
</script>
</body>
</html>

Output

Remaining Balance: 4500

5) Mobile Data Usage

This checks internet data usage.

Rules

Usage ≥ 100 → Limit exceeded
Usage ≥ 80 → Warning
Otherwise normal usage

Program

<!DOCTYPE html>
<html>
<head>
    <title>Data Usage</title>
</head>
<body>
<script>
    let usage = 90;

    if (usage >= 100) {
        document.write("Limit exceeded");
    }
    else if (usage >= 80) {
        document.write("Warning: nearing limit");
    }
    else {
        document.write("Usage normal");
    }
</script>
</body>
</html>

Output

Warning: nearing limit

6) Electricity Bill System

This calculates bill amount based on units consumed.

Rules

0–100 → ₹5/unit
101–300 → ₹7/unit
Above 300 → ₹10/unit

Program

<!DOCTYPE html>
<html>
<head>
    <title>Electricity Bill</title>
</head>
<body>
<script>
    let unit = 40;
    let bill;

    if (unit >= 0 && unit <= 100) {
        bill = 5 * unit;
    }
    else if (unit <= 300) {
        bill = 7 * unit;
    }
    else {
        bill = 10 * unit;
    }

    document.write("Electricity Bill Amount: " + bill);
</script>
</body>
</html>

Output

Electricity Bill Amount: 200

7.Create a JavaScript program to compare the scores of three IPL teams: CSK, MI, and RCB.

The program should:

Take the scores of CSK, MI, and RCB as input.
Compare the scores using nested if–else statements.
Find and print the team with the highest score.
If any two teams have equal scores, print an appropriate message.
If all three teams have the same score, print that all scores are equal.
If two teams share the highest score, print both team names.

Program:

<!DOCTYPE html>
<html>
<head>
    <title>Data Usage</title>
</head>
<body>
<script>
let csk = 180;
let mi = 180;
let rcb = 175;

if (csk > mi) {

    if (csk > rcb) {
        console.log("CSK has highest score");
    } 
    else if (rcb === csk) {
        console.log("CSK and RCB have equal highest score");
    } 
    else {
        console.log("RCB has highest score");
    }

} 
else {

    if (csk === mi) {
        console.log("CSK and MI have equal score");

        if (csk > rcb) {
            console.log("Both CSK and MI are highest");
        } 
        else if (rcb === csk) {
            console.log("All 3 teams have equal scores");
        } 
        else {
            console.log("RCB has highest score");
        }

    } 
    else {

        if (mi > rcb) {
            console.log("MI has highest score");
        } 
        else if (mi === rcb) {
            console.log("MI and RCB have equal highest score");
        } 
        else {
            console.log("RCB has highest score");
        }

    }
}
</script>
</body>
</html>

Output:

CSK and MI have equal score
Both CSK and MI are highest

Truthy and Falsy Values in JavaScript

Kavitha — Tue, 31 Mar 2026 15:17:41 +0000

Truthy and Falsy Values in JavaScript

In JavaScript, values used inside a condition are automatically converted into either true or false.
This concept is called Truthy and Falsy values.
It is very important in conditional statements like if, else, and while.

What are Truthy Values?

A truthy value is any value that JavaScript treats as true when used inside a condition. Examples of Truthy Values

1
-10
"Hello"
"CSK"
[]
{}
true

Example Program

let team = "CSK";

if (team) {
    console.log("Team exists");
}

Output

Team exists

Since "CSK" is a non-empty string, JavaScript treats it as true.

What are Falsy Values?

A falsy value is any value that JavaScript treats as false in a condition.

Falsy Values in JavaScript

There are only a few falsy values:

false
0
""
null
undefined
NaN

Example Program

let score = 0;

if (score) {
    console.log("Pass");
} else {
    console.log("No score");
}

Output

No score

Since 0 is a falsy value, the else block runs.

Simple Example

let name = "";

if (name) {
    console.log("Welcome");
} else {
    console.log("Enter your name");
}

Output

Enter your name

Because an empty string "" is falsy, JavaScript executes the else block.

Why is it Important?

Truthy and falsy values help in:

checking empty input fields
validating forms
checking login details
making decisions in programs

Conclusion
Truthy and falsy values are the foundation of decision making in JavaScript.

Conditional Statements in JavaScript

Kavitha — Tue, 31 Mar 2026 12:57:54 +0000

Conditional Statements in JavaScript

Making Decisions in Code

In JavaScript, conditional statements are used to make decisions in a program.
They help the program choose what action to perform based on whether a condition is true or false.
Conditional statements make your code smart and interactive.

For example:

If the user is 18 or older → allow voting
Else → show not eligible message

JavaScript mainly provides these conditional statements:

if
if...else
if...else if...else
switch

Let’s understand each one with examples.

1) `if` Statement

The if statement is used when you want to execute a block of code only if a condition is true.

Syntax

if (condition) {
    // code to execute
}

Example

let age = 20;

if (age >= 18) {
    console.log("Eligible to vote");
}

Output

Eligible to vote

Here, since age >= 18 is true, the message gets printed.

2) `else` Statement

The else block runs when the condition inside if is false.

Syntax

if (condition) {
    // true block
} else {
    // false block
}

Example

let age = 16;

if (age >= 18) {
    console.log("Eligible to vote");
} else {
    console.log("Not eligible to vote");
}

Output

Not eligible to vote

This is useful when there are two possible outcomes.

3) `else if` Statement

This is used when you need to check multiple conditions.

Syntax

if (condition1) {
    // block 1
} else if (condition2) {
    // block 2
} else {
    // default block
}

Example

let marks = 85;

if (marks >= 90) {
    console.log("Grade A+");
} else if (marks >= 75) {
    console.log("Grade A");
} else if (marks >= 50) {
    console.log("Pass");
} else {
    console.log("Fail");
}

Output

Grade A

The program checks conditions from top to bottom and runs the first true condition.

4) `switch` Statement

The switch statement is used when you want to compare one variable with multiple values.

It is often cleaner than using many else if conditions.

Syntax

switch (expression) {
    case value1:
        // code
        break;
    case value2:
        // code
        break;
    default:
        // default code
}

Example

let day = 3;

switch (day) {
    case 1:
        console.log("Monday");
        break;
    case 2:
        console.log("Tuesday");
        break;
    case 3:
        console.log("Wednesday");
        break;
    default:
        console.log("Invalid day");
}

Output

Wednesday

Why `break` is Important?

The break statement stops the switch after a matching case is found.

Without break, the code continues executing the next cases.

Example Without Break

let day = 1;

switch (day) {
    case 1:
        console.log("Monday");
    case 2:
        console.log("Tuesday");
}

Output

Monday
Tuesday

This happens because there is no break.

Real-Life Example

let temperature = 35;

if (temperature > 30) {
    console.log("It's hot outside");
} else {
    console.log("Weather is cool");
}

Conditional statements help programs make decisions just like humans do.

let team = "CSK";

if (team === "MI") {
    console.log("Mumbai Indians");
} 
else if (team === "CSK") {
    console.log("Chennai Super Kings");
} 
else if (team === "RCB") {
    console.log("Royal Challengers Bengaluru");
} 
else {
    console.log("Invalid Team");
}

Conclusion

Conditional statements are one of the most important concepts in JavaScript.

They help in:

decision making
validating inputs
checking conditions
controlling program flow

DEV Community: Kavitha

Array Iteration Methods in JavaScript

1. forEach() – Perform an action on each element

2. map() – Transform each element

3. filter() – Select elements based on condition

4. reduce() – Reduce array to a single value

5. find() – Get the first matching element

6. some() – Check if at least one element matches

7. every() – Check if all elements match

8. flatMap() – Map + Flatten

9. reduceRight() – Reduce from Right to Left

10. Array.from() – Convert to Array

11. keys() – Get Index Iterator

12. entries() – Get Index + Value

13. values() – Get Values Iterator

14. with() – Replace Value (Non-Mutating)

15. Spread Operator (...) – Expand Array

16. Rest Operator (...) – Collect Values

Conclusion

Callback Functions in JavaScript

Callback Functions in JavaScript

What is a Callback Function?

Syntax

Output

Why Do We Use Callback Functions?

Example 1: Simple Callback

Output

Example 2: Callback with Calculation

Output

Example 3: Callback with setTimeout()

Output

Real-Time Use of Callback Functions

Example: forEach()

Important Note

Conclusion

Arrays in JavaScript

What is an Array?

Accessing Array Elements

Updating Values

Array Length

Looping Through Arrays

Important Built-in Array Methods(To be discussed)

push() – Add element at the end

pop() – Remove last element

shift() – Remove first element

unshift() – Add element at the beginning

Arrays Can Store Multiple Data Types

Is Array a Data Type?

Conclusion

Objects in JS

1) What is an Object?

Syntax

Accessing Object Values

Output

Real-World Example

2) Creating Object Inside an Object

Example: Mobile Object

Access Nested Object

Output

Real-World Understanding

3) Creating Function Inside an Object

Example

Calling the Function

Short Modern Syntax

4) Object + Nested Object + Function Together

Access Everything

Output

Why Do We Use This?

Simple Memory Trick

Looping Programs JS(Part 2)

22. 2^5

23. Decimal to Binary

24. Binary to Decimal

25. Fibonacci Series

26. Swapping Two Numbers

27. Swapping Without Third Variable

28. Fibonacci Without Third Variable

29. Odd Positions & Even Positions

30. First 10 Prime Numbers

31. Sum of Digits Until Single Digit

1. `forEach()` – Perform an action on each element

2. `map()` – Transform each element

3. `filter()` – Select elements based on condition

4. `reduce()` – Reduce array to a single value

5. `find()` – Get the first matching element

6. `some()` – Check if at least one element matches

7. `every()` – Check if all elements match

8. `flatMap()` – Map + Flatten

9. `reduceRight()` – Reduce from Right to Left

10. `Array.from()` – Convert to Array

11. `keys()` – Get Index Iterator

12. `entries()` – Get Index + Value

13. `values()` – Get Values Iterator

14. `with()` – Replace Value (Non-Mutating)

15. Spread Operator (`...`) – Expand Array

16. Rest Operator (`...`) – Collect Values

Example 3: Callback with `setTimeout()`

Example: `forEach()`

`push()` – Add element at the end

`pop()` – Remove last element

`shift()` – Remove first element

`unshift()` – Add element at the beginning

22. `2^5`

33. Printing 110 29 38 47

1) Print `1 1 1 1 1`

2) Print `1 2 3 4 5`

3) Print `1 3 5 7 9`

4) Print `3 6 9 12 15`

1) `for` Loop

2) `while` Loop

1) `1 1 1 1 1`

2) `1 2 3 4 5`

3) `1 3 5 7 9`

4) `3 6 9 12 15`