var findMaxAverage = function (nums, k) {
  var max = 0;
  while (nums.length >= k) {
    a = nums.slice(0, k);
    n = sum(nums.slice(0, k));
    console.log(n);
    if (n > max) {
      max = n;
    }
    nums.shift();
  }
  return max / k;
};
function sum(arr) {
  var s = 0;
  arr.forEach(function (val, idx, arr) {
    s += val;
  }, 0);
  return s;
}
console.log(findMaxAverage([1, 12, -5, -6, 50, 3], 4));