js中str.trim方法

string字符串有trim方法，但trim并非只是处理首尾空格，最近使用时发现有认识上的错误。因此mark下

根据MDN中介绍可以看到，trim处理的是首尾的white space+ line terminators

A new string representing str stripped of whitespace from both its beginning and end. Whitespace is defined as white space characters plus line terminators.

而空格只是其中一种white space。那具体有哪些字符呢

White space

Code point	Name	Abbreviation	Description	Escape sequence
U+0009	Character tabulation		Horizontal tabulation	\t
U+000B	Line tabulation		Vertical tabulation	\v
U+000C	Form feed		Page breaking control character (Wikipedia).	\f
U+0020	Space		Normal space
U+00A0	No-break space		Normal space, but no point at which a line may break
U+FEFF	Zero-width no-break space		When not at the start of a script, the BOM marker is a normal whitespace character.
Others	Other Unicode space characters		Characters in the “Space_Separator” general category

Line terminators

Code point	Name	Abbreviation	Description	Escape sequence
U+000A	Line Feed		New line character in UNIX systems.	\n
U+000D	Carriage Return		New line character in Commodore and early Mac systems.	\r
U+2028	Line Separator		Wikipedia
U+2029	Paragraph Separator		Wikipedia

所以说字符串中首尾包含上述字符在trim后都会被删除。

举例子

这里测试下几个字符

console.log('\r123\r'.trim().length) // 3
console.log('\n123\n'.trim().length) // 3
console.log('    \n123\n'.trim().length) // 3

只处理空格

console.log('    \n123\n'.replace(/^\x20+|\x20+$/g,'').length)

写在最后

之所以发现该问题还是因为程序中字符串被被赋值为\r，而str.trim后会是空字符串，这个不符合预期。因此才重新看下trim逻辑，发现了理解有误