/**
 * @param {number} x
 * @return {number}
 */
var reverse = function(x) {
  let max = Math.pow(2,31) - 1
  let min = Math.pow(-2,31)
  let result = 0, pop
  while(x !== 0){
    pop = x % 10
    x = (x - pop) / 10
    result = result * 10 + pop
  }
  if(result > max || result < min)
    return 0
  return result
}

利用整数取模反转，注意判断溢出情况。