在Javascript中，什么时候以及为什么数字乘以NaN，然后​​求值? [英] When and why number evaluates to NaN, after multiplying, in Javascript?

问题描述

根据我的经验，我知道进行除法运算或尝试从字符串中得出数字(实际上不包含数字)时可以得到NaN.当我可以得到NaN时，还有其他情况吗?特别是-是否可以通过乘法得到它?

From my experience I know, that I can get NaN when doing some division or when trying to make a number out of string, when it actually does not contain a number. Are there any other situations, when I can get a NaN. In particular -- is it possible to get it from multiplication?

这是我在PhoneGap应用程序中使用的一段代码:

This is a piece of code, that I use in my PhoneGap application:

var g = 9.80665;

acceleration.x = (acceleration.x * g).toFixed(2);
acceleration.y = (acceleration.y * g).toFixed(2);
acceleration.z = ((acceleration.z + 1) * g).toFixed(2);

acceleration是基础PhoneGap对象，我几乎不敢相信它包含一个字符串或任何其他值(除float以外)可能会导致NaN.

An acceleration is a base PhoneGap object and I can hardly believe, that it contains a string or any other value, except float, that could result in a NaN.

但是，在某些情况下(在某些特定设备上)，我得到的是NaN.

However, in some certain situations (on some specific devices) I'm getting a NaN out of above.

使用以下代码保护"上述值对我来说不是问题:

It isn't a problem for me to "secure" above values with a code like this:

acceleration.x = (parseFloat(acceleration.x) || 0) + ' m/s\u00b2';
acceleration.y = (parseFloat(acceleration.y) || 0) + ' m/s\u00b2';
acceleration.z = (parseFloat(acceleration.z) || 0) + ' m/s\u00b2';

但是，我真的很好奇，什么时候以及为什么只需做一些值的乘积就可以获得NaN?

But, I'm really curious, when and why I can get a NaN after doing just a multiply of some values?

顺便说一句:我已阅读此和MDN一样好，很多 答案

BTW: I've read this at MDN, as good as many related answers here at Stack Overflow, but to brought me no help or answer to my question.

推荐答案

将数字与无法转换为数字的内容相乘会得到NaN.

You'll get a NaN when multiplying a number with something that can't be converted to a number.

1 * '100'         // 100 because '100' will be converted to 100
1 * ''            // 0 because '' will be converted to 0
1 * 'ten'         // NaN because 'ten' can't be converted to a number
1 * []            // 0 because [] converted to number will be 0
1 * [123]         // 123 because [] will be 123
1 * ['ten']       // NaN
1 * {}            // NaN
1 * true          // 1 because true will be 1
1 * false         // 0
1 * null          // 0
1 * undefined     // NaN, undefined can't be converted to number
1 * function(){}  // NaN

函数'isNaN'检查表达式是否可以转换为数字或不能转换为数字.您需要检查两个数字的乘积，以确认这两个数字都是可以避免错误的数字.

The function 'isNaN' checks if the expression can be converted to a number o not. You culd check both numbers of the multiplication to confirm that both are numbers to avoid errors.

为了完整起见，要知道变量是否完全是NaN，必须将其与自身进行比较:

For the sake of completeness, to know if a variable is exactly NaN you must compare it with itself:

var a = NaN;
if (a != a) console.log('a is NaN');

发生这种情况是因为NaN被定义为与包括自己在内的所有事物都不相等.

It happens because NaN is defined to be unequal to everything, including itself.

这篇关于在Javascript中，什么时候以及为什么数字乘以NaN，然后​​求值?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！