locutus/esm/python/math/factorial.js

Locutus other languages' standard libraries to JavaScript for fun and educational purposes

export function factorial(n) {
    //      discuss at: https://locutus.io/python/factorial/
    // parity verified: Python 3.12
    //     original by: Kevin van Zonneveld (https://kvz.io)
    //          note 1: Returns n! (n factorial)
    //       example 1: factorial(5)
    //       returns 1: 120
    //       example 2: factorial(0)
    //       returns 2: 1
    //       example 3: factorial(1)
    //       returns 3: 1
    const normalized = Number.parseInt(String(n), 10);
    if (normalized < 0) {
        throw new Error('factorial() not defined for negative values');
    }
    if (normalized === 0 || normalized === 1) {
        return 1;
    }
    let result = 1;
    for (let i = 2; i <= normalized; i++) {
        result *= i;
    }
    return result;
}