根据总位数反转一个数字

Question

javascript中是否有内置函数可以根据总数反转一个数字？如果没有如何实施呢？

即

number = 2;
total_number = 10;
__________________
answer = 9;

reverse(2, 10) // returns 9

以来:

 1  == 10
[2  ==  9]
 3  ==  8
 4  ==  7
 5  ==  6
 6  ==  5
 7  ==  4
 8  ==  3
 9  ==  2
 10 ==  1

Answer 1

function (num, total) {
    return total - num + 1;
}