04 - fcc_bonfire_factorialize.js

/*
Return the factorial of the provided integer.
If the integer is represented with the letter n, a factorial is the product of all positive integers less than or equal to n.
Factorials are often represented with the shorthand notation n!
For example: 5! = 1 * 2 * 3 * 4 * 5 = 120f
*/

function factorialize(num) {
    if (num === 0) {
        return 1;
    }
    if (num <= 0) {
        return undefined;
    }
    for (var i = num; --i;) {
        num *=i;
    }
    return num;
}

factorialize(5);