Introduction to javascript regular expressions, regular expressions

Introduction to javascript regular expressions, regular expressions

Overview

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

Basic syntax

Metacharacters

In regular expression mode, some characters have special meanings and are called metacharacters. Metacharacters are matched for a single character.

\ W matches any one of the upper and lower case English characters and numbers 0 to 9 and underline, equivalent to [a-zA-Z0-9 _]

\ W does not match any one of the upper and lower case English characters and numbers 0 to 9, equivalent to [^ a-zA-Z0-9 _]

\ S matches any blank characters, which is equivalent to [\ f \ n \ r \ t \ v]

\ S matches any non-blank characters, which is equivalent to [^ \ s]

\ D matches a single number between 0 and 9, which is equivalent to [0-9]

\ D does not match any single number between 0 and 9, which is equivalent to [^ 0-9]

[\ U4e00-\ u9fa5] matches any single Chinese character (here it uses Unicode encoding to represent Chinese characters)

Identifier

The common Regular Expression Delimiter is a double slash, regex, or/

Atomic Concept

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

[\ F \ n \ r \ t \ v] is an invisible atom. Others indicate visible atoms.

Quantifiers

\ * Matches 0 to multiple metacharacters, equivalent to {0 ,}

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

{N} matches n metacharacters

{N,} matches at least n metacharacters

{N, m} matches n to m metacharacters

\ + Matches at least 1 metacharacter, equivalent to {1 ,}

Boundary

\ B match word boundary

^ The string must start with a specified character

$ The string must end with a specified character

Capture Group

In a regular expression, a number of units (which can be characters or regular expressions) are grouped together to form an independent unit.

In a regular expression, a group is divided into a capture group and a non-capture group.

/(pattern)/flags

Pattern correction

Greedy/lazy, case insensitive, ignore blank characters

Use Cases

Form Verification, template engine

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