es-next-tools/dist/math/factorial.js

A comprehensive utility library for JavaScript and TypeScript that provides a wide range of functions for common programming tasks, including mathematical operations, date manipulations, array and object handling, string utilities, and more.

/**
 * Calculates the factorial of a number.
 * @param {number} n - The number to calculate the factorial of.
 * @returns The factorial of the given number, or NaN if the number is negative.
 * @example
 * factorial(5); // 120
 */
export function factorial(n) {
    if (n < 0)
        return NaN;
    let res = 1;
    for (let i = 2; i <= n; i++) {
        res *= i;
    }
    return res;
}