function quikSort(arr){
if(arr.length<2){
return arr;
}
var left = [],
right = [],
midnum = parseInt(arr.length/2),
mid = arr[midnum];
for(var i = 0;i<arr.length;i++){
if(i!=midnum&&arr[i]<=mid){
left.push(arr[i]);
}
if(i!=midnum&&arr[i]>mid){
right.push(arr[i]);
}
}
/*return quikSort(left).concat(mid).concat(quikSort(right));*/
return [...quikSort(left),mid,...quikSort(right)];
}
console.log(quikSort([3,2,1,5,6]));