Factorial

/**

 * This function provide factorial service

 * 

 * @author  : irfanudin ridho

 * @email   : irfan.ub@gmail.com

 * @date    : December 26, 2010

 * @version : 1.0

 *

 * @param n number a factor of the factorial

 * @return sum total summing of the factor

 */

function factorial(n){
    if (n==0) return 1;
    else if (n<0) return 'invalid factor';
    var sum = 1;
    for(i=n;i>0;i--){
        sum = sum * i;
    }
    return sum;
}