Most efficient way to write Combination and Permutation calculator in Javascript

Question

I have a math website http://finitehelp.com that teaches students Finite Math. I thought it would be cool to include a calculator so I made one for combinations and permutat

Answer 1

As we know, combinations is short for:

So the fastest combinations implement is below:

function factorial(n) {
  let r = 1;
  while (n > 1) r *= n--;
  return r;
}
function combinations(n,r){
    let s = 1;
    let i = r;
    while(i