SOURCE

function quickSort(arr){
    if(arr.length <= 1){
        return arr;
    }
    let left = [];
    let right = [];
    let index = Math.floor(arr.length/2);
    let avg = arr.splice(index,1);
    for(let i = 0; i < arr.length; i++){
        if(arr[i] < avg){
            left.push(arr[i]);
        }else{
            right.push(arr[i]);
        }
    }
    return quickSort(left).concat(avg,quickSort(right));
}
console.log(quickSort([5,2,3,4,2,1,2]))