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));