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This article mainly introduces the analysis of metacharacters and character classes 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
Regular expressions consist of two basic character types:
1. Literal (normal) text characters: characters that represent their own meaning , such as: a, b, c, 1, 2, 3, etc.
2. Metacharacters: Metacharacters are non-letter characters with special meanings in regular expressions. For example, \b
represents a word boundary, which can be the beginning or end of a word.
Common symbol metacharacters:
* + ? $ ^ . | \ () {} []
Generally, one character in a regular expression corresponds to one character in a string. For example, the expression ab\t
means ab
plus a \t
(horizontal tab character).
However, many times, we don’t want to match a certain character, but want to match a certain type of character. At this point, we can use the metacharacter []
to build a simple class.
The so-called class refers to an object that conforms to certain characteristics, a general reference, rather than a specific character. The expression [abc]
groups the characters a
or b
or c
into one category and can match such characters.
Example:
let reg = /[abc]/g let text = 'a1b2c3d4e5' text.replace(reg, 'X') // X1X2X3d4e5
It can be found that when the regular expression matches a
or b
or c
, it is automatically replaced with X
Many times we encounter a situation where we do not want to match certain characters but match others. At this time, you can use character classes to negate - use the metacharacter `^ to create a reverse class, that is, content that does not belong to a certain class.
The expression [^abc]
represents content that is not the characters a
or b
or c
.
Example:
let reg = /[^abc]/g let text = 'a1b2c3d4e5' text.replace(reg, 'X') // aXbXcXXXXX
The result shows that when the expression matches a
or b
or c
, the rest will not be processed. The characters are converted to
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