Answer 1

4
2
1

Answer 2

function reverseNumber (num) {
if ((num / 10 >> 0) === 0) {
return (‘’ + num)
}
return ('' + num % 10 + reverseNumber(num / 10 >> 0) )
}
或者简化成三行代码
function reverseNumber (num) {
return (num / 10 >> 0) === 0 ? ('' + num) : ('' + num % 10 + reverseNumber(num / 10 >> 0) )
}