快速排序算法

    function quickSort(arr,dir) {
        var dir=dir||'add';

        if (arr.length <= 1) { return arr; }
        var pivotIndex = Math.floor(arr.length / 2) ;
        var pivot = arr.splice(pivotIndex, 1)[0];   //基准
        var left = [];
        var right = [];
        if(dir=='add'){   //生序
            for (var i = 0; i < arr.length; i++){
                arr[i] < pivot ? left.push(arr[i]): right.push(arr[i]);
            }
        }else{
            for (var i = 0; i < arr.length; i++){
                arr[i] > pivot ? left.push(arr[i]): right.push(arr[i]);
            }
        }

        return quickSort(left).concat([pivot], quickSort(right))  //不断递归
    };
    var arr=[3,2,67,10,345];

    console.log(quickSort(arr,'aa'))