In-depth understanding of the analysis of predefined classes and boundaries of JS regular expressions-JS Tutorial-php.cn

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

##\d [0-9] Numeric characters \D [^0-9] Non-numeric characters \s [\t\n\x0B\f\r] White space character \S [^\t\n\x0B\f\r] Non-white space character \w [a-zA-Z_0-9] Word characters (letters, numbers, underscores) \W [^a-zA-Z_0-9] Non-word characters ##Use pre Defining classes can quickly match targets, such as matching an ab number and any character. Using character classes and range classes requires writing a lot of code, but using predefined classes only requires writing like this:

Characters	Equivalent classes	Meaning
.	[^\r\n]	Except carriage return and line feed characters All characters

/ab\d/

Copy after login

Boundary

Regular expressions also provide several commonly used boundary matching characters

Characters ^ $ \b ##\B Non-word boundaries When we just want Boundaries are often useful when matching part of a word in a paragraph rather than letters in a word

Meaning
Start with xxx
End with xxx
Word boundaries

Word Boundary vs. Non-Word Boundary

Sometimes, I want to match the is word in a sentence, And I don’t want to match the is letter in the word. At this time, using word boundaries can easily solve this problem:

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

Copy after login

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 reg3 = /\Bis\b/g text.replace(reg3, 'IS') // ThIS is a boy

Copy after login

^ and $ - the beginning and end of

are often used. We will want to match the beginning or end characters, use

^

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

Copy after login

tips: In actual use,^

needs to be written in front of the matching item, while

$Need to unload the rear of the matchIn the case of multiple lines, use ^ and $

In the case of multiple lines, use

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 */

Copy after login

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!