简短的回答是 - 它没有被定义为使用字符串。

The short answer is - it isn't defined to work with strings.

更长的答案：如果你在两个字符串上尝试减法运算符，它将首先将它们转换为数字，然后执行算术运算。

Longer answer: if you try the subtraction operator on two strings, it will first cast them to numbers and then perform the arithmetic.

"10" - "2" = 8

如果您尝试非数字化的东西，则会收到与NaN相关的错误：

If you try something that is non-numeric, you get a NaN related error:

"AA" - "A" = NaN