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This article focuses on "how to understand javascript regular expressions". Interested friends may wish to have a look at it. The method introduced in this paper is simple, fast and practical. Now let the editor take you to learn how to understand javascript regular expressions.

Javascript regular expression:

Regular expressions (English: RegularExpression, often abbreviated as regex, regexp, or RE in code) use a single string to describe and match a series of string search patterns that conform to a syntactic rule.

Search patterns can be used for text search and text replacement.

What is a regular expression?

A regular expression is a search pattern formed by a sequence of characters.

When you search for data in text, you can use search patterns to describe what you want to query.

A regular expression can be a simple character or a more complex pattern.

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Regular expressions can be used for all text search and text replacement operations.

Syntax: / regular expression body / modifier (optional)

Var patt = / runoob/i.

/ runoob/i is a regular expression.

Runoob is a regular expression body (for retrieval).

I is a modifier (search is not case-sensitive).

Regular expression modifier:

I: performs a case-insensitive match.

G: perform a global match (find all matches instead of stopping after the first match is found).

M: perform multi-line matching.

String method:

In JavaScript, regular expressions are commonly used for two string methods: search () and replace ().

The search () method is used to retrieve a specified substring in a string, or to retrieve a substring that matches a regular expression, and returns the starting position of the substring. The position of the substring is sorted by Index.

The replace () method is used to replace some characters in a string with other characters, or to replace a substring that matches a regular expression. First find the location of the element to replace.

Regular expression pattern:

Square brackets are used to find characters in a range:

[abc]: find any character between square brackets.

[0-9]: find any number from 0 to 9.

(X | y): find any options separated by |.

Metacharacters are characters that have a special meaning:

\ d: find the number.

\ s: look for white space characters.

\ b: match word boundaries.

\ uxxxx: find the Unicode character specified in the hexadecimal number xxxx.

Quantifier:

Match: matches any string that contains at least one n.

Match: matches any string that contains zero or more ns.

Match: matches any string that contains zero or one n.

RegExp object:

In JavaScript, the RegExp object is a regular expression object with predefined properties and methods.

The test () method is a regular expression method.

The test () method is used to detect whether a string matches a pattern, and returns true if the string contains matching text, otherwise it returns false.

The exec () method is a regular expression method.

The exec () method is used to retrieve the match of a regular expression in a string.

This function returns an array containing the matching results. If no match is found, the return value is null. The matching result is returned directly.

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