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JavaScript Program to Find the Factorial of a Number

Factorial is a mathematical operation that multiplies a number by all the positive integers less than itself. Represented as n!, it is a key concept in mathematics and is extensively used in combinatorics, algebra, probability, computer science, and algorithmic problem-solving. Factorial calculations are particularly important in understanding permutations, combinations, and various mathematical proofs. For example:

  • 5! = 5 × 4 × 3 × 2 × 1 = 120

  • 0! = 1 (special case by convention)

This tutorial explores multiple JavaScript methods to compute the factorial of a number.

Factorial Program in JavaScript Using for Loop

The simplest way to calculate the factorial of a number is by using a for loop.

Code

function factorialUsingForLoop(number) {
    if (number < 0) {
        return "Factorial of a negative number is not defined.";
    }

    let factorial = 1;
    for (let i = 1; i <= number; i++) {
        factorial *= i;
    }

    return factorial;
}

// Test the function
const num = 5;
console.log(`Factorial of ${num} is ${factorialUsingForLoop(num)}.`);

Output

Factorial of 5 is 120.

Explanation

  • The function initializes factorial to 1.

  • A for loop iterates from 1 to the given number, multiplying factorial by the loop variable i.

  • The result is returned after the loop completes.

This is a simple example of a factorial program in JavaScript using a loop.

JavaScript Program to Check Factorial of Number Using Recursion

A recursive function can be used to calculate the factorial by calling itself.

Code

function factorialUsingRecursion(number) {
    if (number < 0) {
        return "Factorial of a negative number is not defined.";
    }
    if (number === 0 || number === 1) {
        return 1;
    }

    return number * factorialUsingRecursion(number - 1);
}

// Test the function
const num2 = 6;
console.log(`Factorial of ${num2} is ${factorialUsingRecursion(num2)}.`);

Output

Factorial of 6 is 720.

Explanation

  • If the number is less than 0, the function returns an error message.

  • If the number is 0 or 1, the function returns 1 (base case).

  • For other numbers, the function multiplies the number by the factorial of the number minus 1 (recursive case).

This demonstrates a JavaScript program to find factorial of a number using recursion, a commonly used approach in problem-solving.

Factorial of a Number in JavaScript Using while Loop

The while loop can also be used to calculate the factorial of a number.

Code

function factorialUsingWhileLoop(number) {
    if (number < 0) {
        return "Factorial of a negative number is not defined.";
    }

    let factorial = 1;
    let i = 1;
    while (i <= number) {
        factorial *= i;
        i++;
    }

    return factorial;
}
// Test the function
const num3 = 4;
console.log(`Factorial of ${num3} is ${factorialUsingWhileLoop(num3)}.`);

Output

Factorial of 4 is 24.

Explanation

  • The function initializes factorial to 1 and i to 1.

  • The while loop multiplies factorial by i and increments i until i exceeds the given number.

  • The final result is returned after the loop.

This is another way to calculate the factorial in JavaScript using iteration.

Concepts Used in Above Programs

Iteration

  • Loops like for and while are used to repeat tasks efficiently.

Recursion

  • A function calls itself with smaller inputs until a base case is met.

Conditional Statements

  • if conditions handle special cases like negative numbers and base cases.

Multiplication

  • Used to calculate the factorial iteratively or recursively.

Error Handling

  • Ensures that invalid inputs (like negative numbers) are handled gracefully.