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In-depth understanding of the analysis of predefined classes and boundaries of JS regular expressions
In-depth understanding of the analysis of predefined classes and boundaries of JS regular expressions
This article mainly introduces the analysis of predefined classes and boundaries for in-depth understanding of JS regular expressions. It has a certain reference value. Now I share it with you. Friends in need can refer to it.
Preliminary Define classes
Regular expressions provide predefined classes to match common character classes
| Characters | Equivalent classes | Meaning |
|---|---|---|
| . | [^\r\n] | Except carriage return and line feed characters All characters |
| [0-9] | Numeric characters | |
| [^0-9] | Non-numeric characters | |
| [\t\n\x0B\f\r] | White space character | |
| [^\t\n\x0B\f\r] | Non-white space character | |
| [a-zA-Z_0-9] | Word characters (letters, numbers, underscores) | |
| [^a-zA-Z_0-9] | Non-word characters |
/ab\d/
Boundary
Regular expressions also provide several commonly used boundary matching characters
| Meaning | |
|---|---|
| Start with xxx | |
| End with xxx | |
| Word boundaries | ##\B |
let text = 'This is a boy'
let reg1 = /is/g
let reg2 = /\bis\b/g
text.replace(reg1, 'IS') // 没有使用单词边界\b区分，结果为：ThIS IS a boy
text.replace(reg2, 'IS') // 使用了单词边界进行区分，结果为：This IS a boy
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And what should I do when I only want to match the is that is the end of the word? At this time, you can mix word boundaries and non-word boundaries wisely: let text = 'This is a boy' let reg1 = /is/g let reg2 = /\bis\b/g text.replace(reg1, 'IS') // 没有使用单词边界\b区分，结果为：ThIS IS a boy text.replace(reg2, 'IS') // 使用了单词边界进行区分，结果为：This IS a boy
let text = 'This is a boy' let reg3 = /\Bis\b/g text.replace(reg3, 'IS') // ThIS is a boy
^
and$ can perfectly solve this problem:
let text = '@123@abc@' let reg1 = /@/g text2.replace(reg1, 'Q') // 没有使用^和$，匹配了所有的@，结果为：Q123QabcQ let reg2 = /^@/g text.replace(reg2, 'Q') // 使用^匹配开头的@，结果为：Q123@abc@ let reg3 = /@$/g text.replace(reg3, 'Q') // 使用$匹配结尾的@，结果为：@123@abcQ
tips: In actual use, ^ needs to be written in front of the matching item, while $ Need to unload the rear of the match In the case of multiple lines, use ^ and $
m
to enter multiple The line pattern can match the matching characters at the beginning and end of each line:let text = '@123\n@456\n@789'
let reg1 = /^@\d/g
text.replace(reg1, 'Q')
/*
由于换行实际上只是一个换行符字符，在正常模式下，依然看做一段字符
结果为：
Q23
@456
@789
*/
let reg2 = /^@\d/gm
text.replace(reg2, 'Q')
/*
添加了m进入多行模式：
结果为：
Q23
Q56
Q89
*/ The above is the entire content of this article. I hope it will be helpful to everyone's learning. For more related content, please pay attention to the PHP Chinese website! Related recommendations:
In-depth understanding of JS regular expression range analysis
In-depth understanding of JS regular expressions Analysis of metacharacters and character classes
The above is the detailed content of In-depth understanding of the analysis of predefined classes and boundaries of JS regular expressions. For more information, please follow other related articles on the PHP Chinese website!
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