tail-call.js

// file: tail-call.js
// "naive"
function factorial1(x) {
  if (x <= 0) {
    return 1;
  } else {
    return x * factorial1(x-1);
  }
}

// tail rec using a default parameter
function factorial2(n) {
  return facRec2(n);
}
function facRec2(x, acc = 1) {
  if (x <= 1) {
    return acc;
  } else {
    return facRec2(x-1, x*acc);
  }
}

// tail rec
function factorial3(n) {
  return facRec3(n, 1);
}
function facRec3(x, acc) {
  if (x <= 1) {
    return acc;
  } else {
    return facRec3(x-1, x*acc);
  }
}