为什么NaN大于JavaScript中的任何数字？ [英] Why NaN is greater than any number in JavaScript?

问题描述

以下是一个示例：

parseInt(50) > parseInt('a');

在控制台上执行此操作时，它将返回 false 。我的原始代码看起来有点像这样：

When executing this on a console, it will return false. My original code looks somewhat like this:

variableB = parseInt(jQuery('some-element').html());
if(parseInt(variableA) > variableB)
     // do something
else
     // do something else

有时 some-element 将不会被填充，因此返回 NaN 。发生这种情况时，我确实希望执行 else 块。我实际上得到了我的期望，但我只是想确保它确实打算以这种方式工作。

Sometimes the some-element will not be filled and thus return NaN. When this happens, I do want the else block to be executed. I am actually getting what I expect, but I just want to make sure that it indeed is intended to work this way.

推荐答案

在IEEE 754 arithmethic中， JavaScript使用的浮点模型<根据定义，/ a>， NaN （或非数字）不小于，等于或大于任何其他数字。

In IEEE 754 arithmethic, the floating-point model used by JavaScript, NaN (or not-a-number) is, by definition, not less than, equal to, or greater than any other number.

请注意，这甚至适用于两个 NaN ：如果 x = NaN 和 y = NaN ，比较 x === y 将返回false。

Notice that this even applies to two NaNs: if x = NaN and y = NaN, the comparison x === y will return false.

下面我引用 IEEE 754标准（第5.11节）指定了此行为：

Below I quote the portion of the IEEE 754 Standard (Section 5.11) where this behavior is specified:

可能存在四种相互排斥的关系：比，等于，
大于和无序。当至少一个
操作数是 NaN 时，会出现最后一种情况。每个 NaN 都应将无序与
的所有内容进行比较，包括其自身。

Four mutually exclusive relations are possible: less than, equal, greater than, and unordered. The last case arises when at least one operand is NaN. Every NaN shall compare unordered with everything, including itself.

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