old_contents: // Sort array using heap sort
  
  // main heap sort function
  function heapSort(arr) {
  	var len = arr.length,
  		end = len - 1;
  
  	heapify(arr, len);
  
  	while (end > 0) {
  		swap(arr, end--, 0);
  		siftDown(arr, 0, end);
  	}
  
  	return arr;
  }
  
new_contents: // Sort array using heap sort
  
  // main heap sort function
  function heapSort(arr) {
  	var len = arr.length,
  		end = len - 1;
  
  	heapify(arr, len);
  
  	while (end > 0) {
  		swap(arr, end--, 0);
  		siftDown(arr, 0, end);
  	}
  
  	return arr;
  }
  
  // function to make array heap tree
  function heapify(arr, len) {
  	// break array into root and two sides to create heap tree
  	var middle = Math.floor((len - 2)/2);
  	while (middle >= 0) {
  		siftDown(arr, middle--, len - 1);
  	}
  }
  
subject: Add function to make array a heap tree