Combinations with(out) repetitions

function binomial(n, k, e) {
    /**
    **If e is even calculating for combinations with repetitions - (n+k-1)! / (k! * (n-1)!)
    **Else for combinations without repetitions - n! / (k! * (n-k)!)
    ***/
    var numerator = 1, denominator = 1;
    if (k > n - k && e % 2 === 1) k = n - k; //possible reducing k if looking for combinations without repetitions
    for (var i = 0; i < k; i++) {
        numerator *= n + i * Math.pow(-1, e);
        denominator *= k - i;
    }

    return formatting(numerator / denominator);
}

function formatting(string) {
    return string.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
}

console.log(binomial(10, 8, 1));
console.log(binomial(10, 8, 2));