Description of JavaScript Regular expressions _ regular expressions

Overview

A regular expression is a set of rules that are declared in advance to match characters in a string.

Basic syntax

Metacharacters

In the pattern of regular expressions, there are some characters that have special meaning and are called meta characters. Metacharacters are matched for a single character.

\w match uppercase and lowercase characters and numbers 0 to 9 of any and underscore, equivalent to [a-za-z0-9_]

\w does not match the size of the English character and the number 0 to 9 of any one, equivalent to [^a-za-z0-9_]

\s matches any whitespace character, equivalent to [\f\n\r\t\v]

\s matches any non-white-space character, equivalent to [^\s]

\d matches any single number from 0 to 9, equivalent to [0-9]

\d does not match any single number from 0 to 9, equivalent to [^0-9]

[\U4E00-\U9FA5] matches any single Chinese character (Unicode encoding is used here to denote Chinese characters)

Defining character

The more common regular expression qualifier is the double slash/regex/

The concept of atoms

The atoms in the regular expression are divided into visible atoms and invisible atoms.

[\f\n\r\t\v] belongs to invisible atoms, others represent visible atoms

Quantifiers

\* matches 0 to multiple metacharacters, equal to {0,}

? Matches 0 to 1 metacharacters, equivalent to {0,1}

{n} matches n-ary characters

{N,} matches at least n metacharacters

{N,m} matches n to M metacharacters

\+ matches at least 1 metacharacters, equal to {1,}

Boundary

\b Match word boundaries

^ string must start with the specified character

The $ string must end with the specified character

Capturing groupings

In regular expressions, use () to organize several units (which can be characters, regular expressions) together to become a self-contained unit.

In regular expressions, groupings are grouped into capture groupings and non-capture groupings.

/(Pattern)/flags

Mode correction

Greedy/lazy, ignoring case, ignoring whitespace characters

Working with scenes

form validation, template engine

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