Array.prototype.swap = function(x,y) {

    if(this[x] == undefined || this[y] == undefined) return;

    var temp = this[x];
    this[x] = this[y];
    this[y] = temp;

};

var MaxHeapify = function(A,i) {

    var l = 2*i;
    var r = 2*i +1;
    var largest = i;
    if(l <= heap_size && A[l] > A[largest]) {
        largest = l;
    }
    if(r <= heap_size && A[r] > A[largest]) {
        largest = r;
    }
    if (largest != i) {
        A.swap(i,largest);
        MaxHeapify(A,largest);
    }


};

var BuildMaxHeap = function(A) {

    var middle = Math.floor(A.length  / 2);
    for(var i=middle; i>=1;i--) {
        MaxHeapify(A,i);
    }


};

var HeapSort = function(A) {

    BuildMaxHeap(A);
    for(var i=A.length;i>=2;i--) {
        A.swap(1,i);
        heap_size--;
        MaxHeapify(A,1);

    }

};

var arr = [null,4,8,1,3,2,15,9,10,14,8,7];
var heap_size = arr.length;
HeapSort(arr);

console.log(arr);