Javascript Algorithm Array Sort Quick Sort 2

function getRandomInt(min, max) {
  return Math.floor(Math.random() * (max - min + 1)) + min;
}

function swap(a,i,j){
  var tmp = a[i];
  a[i] = a[j];//  ww w. j a  v  a  2s .c o  m
  a[j] = tmp;
}

function partition(a,left,right){
  left  = left ? left : 0;
  right  = right ? right : a.length-1;

  var i  = left+1,
    j  = right,
    p  = left;

  while( i<=j ){
    while( a[i]<a[p] ){ 
      i+=1; 
    }
    while( a[j]>a[p] ){
      j-=1;
    }

    if( i<j ){
      swap(a,i,j);
      i+=1;
      j-=1;
    }
  }
  swap(a,p,j);

  return j;

}


function quicksort(a,left,right){
  var k  = 0,
    m  = 0;
  left  = left ? left : 0;
  right  = right ? right : a.length-1;

  if( left<right ){
    k = getRandomInt(left,right);
    swap(a,left,k);
    m = partition(a,left,right);
    quicksort(a,left,m-1);
    quicksort(a,m+1,right);
  }
}


var a = [-1,5,11,-124,6,7,1,3,99,987,55,24,12];
quicksort(a);
console.log(a);