编辑代码

let num = 12345
const reverse = function (num) {
    let numStr = num.toString()
    let numArr = numStr.split('')
    let res = 0
    if (numArr[0] !== '-') {
        res = numArr.reverse().join('') - 0
    } else {
        res = numArr.reverse().join('')
        res = '-' + res.replace(/-/, '') - 0
    }

    if (res <= Math.pow(2, 31) && res >= Math.pow(-2, 31)) {
        return res
    } else {
        return 0
    }
}

console.log(num, '->', reverse(num))