什么是Javascript中的32位整数？

我正在做一些编码挑战,遇到了一些我不太熟悉的东西.我更好奇地了解它是什么以及它为什么存在.

提示非常简单: Given a 32-bit signed integer, reverse digits of an integer.

Example:
Input: -123
Output: -321

Example:    
Input: 120
Output: 21

Assume we are dealing with an environment which could only hold integers within the 32-bit signed integer range. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

我想出了这个.

var reverse = function(x) {
    var isNegative = false;
    if(x <0){
        isNegative = true;
        x *= -1;
    };
    var reverseX = parseInt(String(x).split('').reverse((a,b) => a - b).join(''));
    if(reverseX > Math.pow(2,32)){
      return 0;
    }
    if(isNegative){
        return -1 * reverseX
    } else {
        return reverseX;
    }
};

但是,我对一些失败的测试感到难过:

Input:
1563847412
Output:
2147483651
Expected: 0

根据我的理解,32位整数是2 ^ 32.它在JS中的意义是什么？如果我开始过去会发生什么？(2^32 + 1)

我的第二个问题,如果我可能会问两个,我是"预期",如果价值reverseX超过2 ^ 32,但它仍然没有通过测试.

   if(reverseX > Math.pow(2,32)){
      return 0;
    }

0当我超过32位整数时,如何正确返回？

有符号整数的上限不是2 ³² - 1,而是2 ³¹ - 1,因为第一位是符号位.

如果进行比较,您将看到您的测试给出了正确的结果.

请注意,Javascript 对数字使用IEEE-754浮点表示,即使它们是整数.但是浮点精度足以在32位整数上执行精确计算.如您所知,您需要进行必要的测试以检测32位溢出.

关于你的代码的一些注释:它将一个参数传递给Array#reverse方法,这是一个不带参数的方法.我将如何编写它 - 请参阅代码中的注释:

// Name argument n instead of x, as that latter is commonly used for decimal numbers 
function reverse(n) {
    // Array#reverse method takes no argument.
    // You can use `Math.abs()` instead of changing the sign if negative.
    // Conversion of string to number can be done with unary plus operator.
    var reverseN = +String(Math.abs(n)).split('').reverse().join('');
    // Use a number constant instead of calculating the power
    if (reverseN > 0x7FFFFFFF) {
        return 0;
    }
    // As we did not change the sign, you can do without the boolean isNegative.
    // Don't multiply with -1, just use the unary minus operator.
    // The ternary operator might interest you as well (you could even use it
    //    to combine the above return into one return statement)
    return n <0 ? -reverseN : reverseN;
}

console.log(reverse(-123));
console.log(reverse(1563847412));

Input:
1563847412
Output:
2147483651
Expected: 0