In-depth understanding of the analysis of metacharacters and character classes in JS regular expressions

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

元Characters and character classes

Metacharacters

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:

* + ? $ ^ . | \ () {} []

Character class

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

Character class inversion

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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