写js时出现一个问题，想不通为什么，求大神解释

function maxSubSum(arr,left,right){

        //console.log(right);
        var leftMaxSum = rightMaxSum = 0;
        //将这俩行代码放这里就会出错，是因为什么？
        // var leftMaxBorderSum = rightMaxBorderSum = 0;
        // var lefttemp = righttemp = 0;

        if(left == right){
            if(arr[left] > 0){
                return arr[left];
            }else{
                return 0;
            }
        }
        var center = Math.floor((left + right)/2);
        var leftMaxSum = maxSubSum(arr,left,center);
        var rightMaxSum = maxSubSum(arr,center+1,right);

        //console.log(leftMaxBorderSum,rightMaxBorderSum);
        //把代码放这里就不会出错，是因为什么？
        var leftMaxBorderSum = rightMaxBorderSum = 0;
        var lefttemp = righttemp = 0;
        for(var i=center; i>=left; i--){
            lefttemp += arr[i];
            if(lefttemp >= leftMaxBorderSum){
                leftMaxBorderSum = lefttemp;
            }
        }

        for(var j=center+1; j<=right; j++){
            righttemp += arr[j];
            //console.log(j);
            if(righttemp >= rightMaxBorderSum){
                rightMaxBorderSum = righttemp;
            }
        }
        console.log('['+left+','+right+']');
        console.log(center+','+leftMaxSum+','+rightMaxSum+','+ (leftMaxBorderSum + rightMaxBorderSum));
        return Math.max(leftMaxSum,rightMaxSum,(leftMaxBorderSum + rightMaxBorderSum));
    }

    var arr = [4,-3,5,-2,-1,2,6,-2];
    console.log(maxSubSum(arr,0,7));

声明定义语句写在递归调用前，产生的答案是错的。但是声明定义语句写在递归调用后，答案就是正确。我觉得有可能跟作用域链有关系，
但是想不通为什么，求大神给解释解释。