LeetCode reverse integer - JavaScript

Subject description:

Given a 32-bit signed integer, the integer number is reversed. Requirements are as follows:

Only digital flip, flip the sign bit is not.
We assume that the environment can only store a 32-bit signed integer, which is the numerical range [-231 231--1]. If the reverse integer overflow, 0 is returned.

示例：
输入: 123
输出: 321
输入: -123
输出: -321
输入: 120
输出: 21
输入: 2147483649
输出: 0

Solution:

var reverse = function(x){
    var resultArr = [];
    var resultNum;
    resultArr = x.toString().split("");
    if(resultArr[0] == "-"){
        resultArr.shift();
        resultArr.reverse().unshift("-");
        resultNum = resultArr.join("");
    }else{
       resultNum = resultArr.reverse().join("");
    }
    resultNum = parseInt(resultNum);
    if(resultNum > Math.pow(2,31)-1 || resultNum < -Math.pow(2,31)){
        return 0;
    }
    return resultNum;
};