JS regular expressions from getting started to being buried (4)--predefined classes and boundaries

Pre-defined Classes

Regular expressions provide pre-defined classes to match common character classes

character	Equivalence class	meaning
.	[^\r\n]	All characters except carriage return and line break
\d	[0-9]	numeric characters
\d	[^0-9]	Non-numeric characters
\s	[\t\n\x0b\f\r]	whitespace characters
\s	[^\t\n\x0b\f\r]	Non-whitespace characters
\w	[A-za-z_0-9]	Word characters (Letters, numbers, underscores)
\w	[^a-za-z_0-9]	Non-word characters

Using predefined classes can quickly match a target, such as: Match a ab+ number + any character, use a character class, a range class to write a large amount of code, and use a predefined class to write only:

/ab\d/

Boundary

Regular expressions also provide several commonly used boundary-matching characters

character	meaning
^	Start with XXX
$	End With XXX
\b	Word boundaries
\b	Non-word boundary

Boundaries are often useful when we want to match only some of the words in a word, not the letters in the words.

Word boundaries and non-word boundaries

Sometimes, I want to match the is word in a sentence rather than match the is letter in the word, at which point the word boundary can be used to solve the problem easily:

let text = ‘This is a boy‘let reg1 = /is/glet reg2 = /\bis\b/gtext.replace(reg1, ‘IS‘)    // 没有使用单词边界\b区分，结果为：ThIS IS a boytext.replace(reg2, ‘IS‘)    // 使用了单词边界进行区分，结果为：This IS a boy

And what if I just want to match the is at the end of the word? The word boundary and non-word boundaries can be mixed wit:

let text = ‘This is a boy‘let reg3 = /\Bis\b/gtext.replace(reg3, ‘IS‘)    // ThIS is a boy

^ and $--start with end

Many use, we would like to match the beginning or end of the character, use ^ and $ can perfectly solve this problem:

let text = ‘@[email protected]@‘let reg1 = /@/gtext2.replace(reg1, ‘Q‘)    // 没有使用^和$，匹配了所有的@，结果为：Q123QabcQlet reg2 = /^@/gtext.replace(reg2, ‘Q‘)     // 使用^匹配开头的@，结果为：[email protected]@let reg3 = /@$/gtext.replace(reg3, ‘Q‘)     // 使用$匹配结尾的@，结果为：@[email protected]

Tips: The actual use ^ needs to be written in front of the match, and $ need to unload the match after the

Use ^ and $ in multi-line cases

In the case of multiple rows, use the m enter multiline mode to match the beginning and end of each line to match the character:

let text = ‘@123\[email protected]\[email protected]‘let reg1 = /^@\d/gtext.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/gmtext.replace(reg2, ‘Q‘)/*    添加了m进入多行模式：    结果为：    Q23    Q56    Q89*/

JS regular expressions from getting started to being buried (4)--predefined classes and boundaries