Heapsort in Javascript

function heapSort(array) {
  let size = array.length

  // build heapSort (rearrange array)
  for (let i = Math.floor(size / 2 - 1); i >= 0; i--)
    heapify(array, size, i)

  // one by one extract an element from heapSort
  for (let i = size - 1; i >= 0; i--) {
    // move current root to end
    let temp = array[0]
    array[0] = array[i]
    array[i] = temp

    // call max heapify on the reduced heapSort
    heapify(array, i, 0)
  }
}

// to heapify a subtree rooted with node i which is an index in array[]
function heapify(array, size, i) {
  let max = i // initialize max as root
  let left = 2 * i + 1
  let right = 2 * i + 2

  // if left child is larger than root
  if (left < size && array[left] > array[max])
    max = left

  // if right child is larger than max
  if (right < size && array[right] > array[max])
    max = right

  // if max is not root
  if (max != i) {
    // swap
    let temp = array[i]
    array[i] = array[max]
    array[max] = temp

    // recursively heapify the affected sub-tree
    heapify(array, size, max)
  }
}

let array = [12, 11, 15, 10, 9, 1, 2, 3, 13, 14, 4, 5, 6, 7, 8]
heapSort(array)
alert(array)