javascript 与字边界相比，正则表达式 (\B) 中的非字边界是什么？
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What are non-word boundary in regex (\B), compared to word-boundary?
提问by DarkLightA
What are non-word boundary in regex (\B), compared to word-boundary?
与字边界相比，正则表达式 (\B) 中的非字边界是什么？
回答by Mark Byers
A word boundary (\b) is a zero width match that can match:
单词边界 ( \b) 是零宽度匹配，可以匹配：
- Between a word character (
\w) and a non-word character (\W) or - Between a word character and the start or end of the string.
- 在单词字符 (
\w) 和非单词字符 (\W) 之间或 - 在单词字符和字符串的开头或结尾之间。
In Javascript the definition of \wis [A-Za-z0-9_]and \Wis anything else.
在 Javascript 中，\wis[A-Za-z0-9_]和\Wis的定义是其他任何东西。
The negated version of \b, written \B, is a zero width match where the above does nothold. Therefore it can match:
否定版本的\b，写\B，是零宽度匹配，其中上面并不成立。因此它可以匹配：
- Between two word characters.
- Between two non-word characters.
- Between a non-word character and the start or end of the string.
- The empty string.
- 在两个单词字符之间。
- 在两个非单词字符之间。
- 在非单词字符和字符串的开头或结尾之间。
- 空字符串。
For example if the string is "Hello, world!"then \bmatches in the following places:
例如，如果字符串"Hello, world!"，然后\b在以下地方匹配：
H e l l o , w o r l d !
^ ^ ^ ^
And \Bmatches those places where \bdoesn't match:
并\B匹配那些\b不匹配的地方：
H e l l o , w o r l d !
^ ^ ^ ^ ^ ^ ^ ^ ^ ^
回答by derenio
The basic purpose of non-word-boundaryis to created a regex that says:
的基本目的non-word-boundary是创建一个正则表达式，它说：
if we are at the beginning/end of a
word char(\w=[a-zA-Z0-9_]) make sure the previous/next character is also aword char,e.g.:
"a\B."~"a\w":"ab","a4","a_", ... but not"a ","a."if we are at the beginning/end of a
non-word char(\W=[^a-zA-Z0-9_]) make sure the previous/next character is also anon-word char,e.g.:
"-\B."~"-\W":"-.","- ","--", ... but not"-a","-1"
如果我们在 a
word char(\w=[a-zA-Z0-9_])的开头/结尾，请确保前一个/下一个字符也是 aword char，例如：
"a\B."〜"a\w"："ab","a4","a_", ... 但不是"a ","a."如果我们在 a
non-word char(\W=[^a-zA-Z0-9_])的开头/结尾，请确保前一个/下一个字符也是 anon-word char，例如：
"-\B."〜"-\W"："-.","- ","--", ... 但不是"-a","-1"
For word-boundaryit's similar but instead of making sure that the adjacent characters are of the same class (word char/non-word car) they need to differ, hence the name word's boundary.
因为word-boundary它是相似的，但不是确保相邻字符属于同一类（word char/ non-word car），它们需要不同，因此名称word's boundary.
