HeapSort.js

function heapSort(arr){
  var len = arr.length,
      end = len-1;

  heapify(arr, len);
  
  while(end > 0){
   swap(arr, end--, 0);
   DownHeapify(arr, 0, end);
  }
  return arr;
}
    
function heapify(arr, len){
   // breaking the array into root + two sides, to create tree (heap)
   var mid = Math.floor((len-2)/2);
   while(mid >= 0){
    DownHeapify(arr, mid--, len-1);    
  }
}

function DownHeapify(arr, start, end){
   var root = start,
       child = root*2 + 1,
       toSwap = root;
   while(child <= end){
      if(arr[toSwap] < arr[child]){
        swap(arr, toSwap, child);
      }
      if(child+1 <= end && arr[toSwap] < arr[child+1]){
        swap(arr, toSwap, child+1)
      }
      if(toSwap != root){
         swap(arr, root, toSwap);
         root = toSwap;
      }
      else{
         return; 
      }
      toSwap = root;
      child = root*2+1
  }
}


function swap(arr, i, j){
  var temp = arr[i];
  arr[i] = arr[j];
  arr[j] = temp;
}