为什么 ('b'+'a'+ + 'a' + 'a').toLowerCase() 'banana' 的结果是?

Why is the result of (#39;b#39;+#39;a#39;+ + #39;a#39; + #39;a#39;).toLowerCase() #39;banana#39;?(为什么 (b+a+ + a + a).toLowerCase() banana 的结果是?)

问题描述

当我的一个朋友偶然发现这段 JavaScript 代码时，我正在练习一些 JavaScript:

I was practicing some JavaScript when one of my friends came across this JavaScript code:

document.write(('b' + 'a' + + 'a' + 'a').toLowerCase());

以上代码回答"banana"！谁能解释一下为什么?

The above code answers "banana"! Can anyone explain why?

推荐答案

+'a' 解析为 NaN ("Not a Number") 因为它强制转换为字符串为数字，而字符 a 不能被解析为数字.

+'a' resolves to NaN ("Not a Number") because it coerces a string to a number, while the character a cannot be parsed as a number.

document.write(+'a');

小写变成banana.

"ba"加上NaN，由于类型转换，将NaN变成字符串"NaN"，给出 baNaN.然后后面有一个a，给出baNaNa.

Adding NaN to "ba" turns NaN into the string "NaN" due to type conversion, gives baNaN. And then there is an a behind, giving baNaNa.

+ + 之间的空格是为了使第一个字符串连接和第二个一元加号(即正")运算符.如果你使用 'ba'+(+'a')+'a' 得到相同的结果，解析为 'ba'+NaN+'a'，即由于类型杂耍，相当于 'ba'+'NaN'+'a'.

The space between + + is to make the first one string concatenation and the second one a unary plus (i.e. "positive") operator. You have the same result if you use 'ba'+(+'a')+'a', resolved as 'ba'+NaN+'a', which is equivalent to 'ba'+'NaN'+'a' due to type juggling.

document.write('ba'+(+'a')+'a');

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