JavaScript Program to Find the Factorial of a Number

Introduction

The factorial of a number is the product of all positive integers less than or equal to that number. It is denoted as n!. For example, the factorial of 5 is 5! = 5 * 4 * 3 * 2 * 1 = 120. Factorials are used in many areas of mathematics, especially in combinatorics, algebra, and calculus. This program helps calculate the factorial of a given number in JavaScript.

Problem Statement

Create a JavaScript program that:

• Accepts a positive integer.
• Calculates and returns the factorial of that number.

Example:

• Input: 5

• Output: 120

• Input: 3

• Output: 6

Solution Steps

1. Read the Input Number: Provide the number either as user input or directly within the code.
2. Handle Edge Case: If the input number is 0, return 1 as 0! = 1.
3. Calculate the Factorial: Use either an iterative loop or recursion to calculate the factorial.
4. Display the Result: Print the calculated factorial.

JavaScript Program

// JavaScript Program to Find the Factorial of a Number
// Author: https://www.javaguides.net/

function factorial(n) {
    // Step 1: Handle base case
    if (n === 0 || n === 1) {
        return 1;
    }

    // Step 2: Calculate the factorial iteratively
    let result = 1;
    for (let i = 2; i <= n; i++) {
        result *= i;
    }
    return result;
}

// Example input
let inputNumber = 5;
let result = factorial(inputNumber);
console.log(`The factorial of ${inputNumber} is: ${result}`);

Output

The factorial of 5 is: 120

Example with Different Input

let inputNumber = 3;
let result = factorial(inputNumber);
console.log(`The factorial of ${inputNumber} is: ${result}`);

Output:

The factorial of 3 is: 6

Explanation

Step 1: Handle the Base Case

• If the number is 0 or 1, the factorial is defined as 1, so the program returns 1 immediately for these values.

Step 2: Calculate the Factorial Iteratively

• For numbers greater than 1, the function uses a for loop to calculate the factorial by multiplying the result variable with each number from 2 to n.

Step 3: Display the Result

• The calculated factorial is printed using console.log().

Conclusion

This JavaScript program demonstrates how to calculate the factorial of a given number using an iterative approach. Factorials are a fundamental mathematical concept, and this program provides a simple and efficient way to compute them in JavaScript. You can modify this solution to use recursion or handle larger inputs if needed.