Quicksort in JavaScript

// replace array with string concatenation for better performance

function quickSort(list) {
    if (!list.length) return [];
 
    var left = [],
        right = [],
        center = list[0];
 
    for (var i = 1; i < list.length; i++) {
        if (list[i] < center) {
            left.push(list[i]);
        }
        else {
            right.push(list[i]);
        }
    };
 
    return quickSort(left) + center + ',' + quickSort(right);
}