var quickSort = function(arr){
     
     if(arr.length<=1){return arr;}

     var pivotIndex = Math.floor(arr.length/2);
     var pivot = arr.splice(pivotIndex,1)[0];

     var left = [];
     var right = [];

     for(var i=0;i<arr.length;i++){
         if(arr[i]<pivot){
             left.push(arr[i]);
         }else{
             right.push(arr[i]);
         }
     }
    return quickSort(left).concat([pivot],quickSort(right))    ;
 
};

var arr = [5,100,6,3,-12];
document.write(quickSort(arr));