js中str.trim方法
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1 min read
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
strstripped 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
