关于快速排序

var a = [5,29,23,37,27,44];
function sortNum(a,b){
        return a-b;    
    }
alert(a.sort(sortNum));

var a = [5,29,23,37,27,44];
    function quickSort(arr){
        if(arr.length <=1){
            return arr;    
        }
        var num = Math.floor(arr.length/2);
        var numValue = arr.splice(num,1);
        var left = [];
        var right = [];
        for(var i =0,len=arr.length;i<len;i++){
            if(arr[i]<numValue){
                left.push(arr[i]);    
            }
            if(arr[i]>numValue){
                right.push(arr[i]);    
            }
            
        }
        return quickSort(left).concat(numValue,quickSort(right));
        
    }
    alert(quickSort(a));