javascript - 为什么（'b'+'a'+ +'a'+'a'）。toLowerCase（）'banana'的结果？(Why is the result of ('b'+'a'+ + 'a' + 'a').toLowerCase() 'banana'?)

Question

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

(当我的一个朋友遇到以下JavaScript代码时，我正在练习一些JavaScript：)

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

The above code answers "banana" !

(上面的代码回答"banana" ！)

Can anyone explain why?

(谁能解释为什么？)

  ask by HV Sharma translate from so

Answer 1

+'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.

(+'a'解析为NaN （“非数字”），因为它将字符串强制为数字，而字符a不能解析为数字。)

 document.write(+'a'); 

To lowercase it becomes banana .

(小写变成banana 。)

Adding NaN to "ba" turns NaN into the string "NaN" due to type conversion, gives baNaN .

(将NaN添加到"ba"会由于类型转换而将NaN变成字符串"NaN" ，得到baNaN 。)

And then there is an a behind, giving baNaNa .

(然后是a后面是baNaNa 。)

The space between + + is to make the first one string concatenation and the second one a unary plus (ie "positive") operator.

(+ +之间的空格是使第一个字符串串联，而第二个字符串成为一元加号（即“正”）运算符。)

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.

(如果使用'ba'+(+'a')+'a' ，则得到相同的结果，解析为'ba'+NaN+'a' ，等效于'ba'+'NaN'+'a'打杂耍。)

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