midpoint 2d displacement in js

gistfile1.txt

function midpoint(arr, p1, p2, max, jitter) {
  var mid = Math.round((p1 + p2) / 2);
  if (p2 - p1 <= 1 || p2 === mid || p1 === mid) {
      return;
  }
  arr[mid] = ((arr[p1] + arr[p2]) / 2) + (max * (Math.random() * (jitter * 2) - jitter));
  midpoint(arr, p1, mid, max / 2, jitter);
  midpoint(arr, mid, p2, max / 2, jitter);
}