SOURCE

const arr = [20,3,11,4,15,8,7,6,9,0];
function swap(array, indexA, indexB) {
  const temp = array[indexA];
  array[indexA] = array[indexB];
  array[indexB] = temp;
}
function maxHeapify(array, index, heapSize) {
  	let max = index;
    const left = index * 2 + 1,
        	right = index*2 + 2;
  	if (left <= heapSize && array[left] > array[max]) {
      max = left;
    }
  	if (right <= heapSize && array[right] > array[max]) {
      max = right;
    }
  	if (max !== index) {
      swap(array, index, max);
      maxHeapify(array, max, heapSize);
    }
}
function buildHeap(array) {
  	const lastNotLeaf = Math.floor((array.length -1) / 2);
  	for (let i = lastNotLeaf; i >= 0; i-- ) {
      maxHeapify(array, i, array.length-1);
    }
}

function heapSort(array) {
	buildHeap(array);
  for (let i = array.length-1; i >= 0; i--) {
    swap(array, 0, i);
    maxHeapify(array, 0, i-1);
  }
}

heapSort(arr)
console.log(arr);