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What is a regular expression?

/ / regular expression (regular expression) is an object that describes character patterns

/ / JS defines RegExp classes to represent regular expressions

/ / both String and RegExp define functions that use regular expressions for powerful pattern matching and text retrieval and replacement

Second, create regular expressions

1. Create a regular expression

/ / JS provides two ways to create rules; one is to use the new operator, and the other is to use a literal quantity.

(1) .var box = new RegExp ('box'); / / the first parameter is a string

Var box = new RegExp ('box','ig'); / / the second parameter is the optional mode modifier

(2). Var box = / box/; / / use two backslashes directly

Var box = / box/ig; / / add mode modifier

2.RegExp object tests regular expressions

/ / the RegExp object contains two methods: test () and exec (), which are similar in function and are used to test string matching.

(1) .test (): finds whether a specified regular expression exists in a string and returns a Boolean value

/ / test () instance

Var pattern = new RegExp ('box','i'); / / create a regular

Var str = 'This is a Boxboy strings; / / create a string

Alert (pattern.test (str)); / / verify the match through the test () method

/ / use a statement to achieve regular matching

Alert (/ box/i.test ('This is a boxboxes'))

(2) .exec (): finds the specified regular expression in a string, returns an array of relevant information containing the lookup string if successful, and returns null if it fails.

Exec () instance

Var pattern = / box/i

Var str = 'This is a Boxbox'

Alert (pattern.exec (str)); / / matching returned an array

3.String object tests regular expressions

(1) .match (pattern): returns a substring or null in pattern

/ / math () method to get the matching array

Var pattern = / box/ig; / / Global is turned on

Var str = 'This is a Boxer, that is a Box toothing'

Alert (str.match (pattern)); / / get the array: [Box,Box]

(2) .search (pattern): returns the starting position of pattern in the string

Var pattern = / box/ig

Var str = 'This is a Boxer, that is a Box toothing'

Console.log (str.search (pattern)); / / 10 position search () returns as soon as it is found, otherwise-1 is returned

(3) .replace (pattern,replacement): replace pattern with replacement

Var pattern = / box/ig

Var str = 'This is a Boxboy' that is a Box too'

Console.log (str.replace (pattern,'Tom')); / / replace Box with Tom

(4) .split (pattern): returns an array of strings split according to the specified pattern

Var pattern = / / ig

Var str = 'This is a boxes, That is a Box too.'

Console.log (str.split (pattern)); / / splits spaces into an array

Three acquisition control

/ / regular expression metacharacters are characters with special meanings.

/ / they have some special functions that can control how patterns are matched.

/ / the metacharacter after the backslash will lose its special meaning

1. Metacharacter / meta-symbol matching

/ / character classes: single characters and numbers

. Match any character except a newline character

[a-z0-9] matches any character in the character set in parentheses

[^ a-z0-9] matches characters in a character set that is not in parentheses

\ d matching numbers

\ d match non-numeric

\ w match letters and numbers and _

\ W matches non-letters and numbers and _

/ / character class: White space character

\ 0 match null character

\ b match space characters

\ f match feed characters

\ nmatch newline character

\ r match carriage return character

\ t match configuration table character

\ s matches white space characters / spaces / tabs and newline characters

\ s matches non-white space characters

/ / character class: anchor character

^ match at the beginning of the line

Match at the end of the line

/ / character class: repeating characters

X? Match 0 or 1 x

X * match 0 or any number of x

X + matches at least one x

(xyz) + match at least one (xyz)

X {mdirection n} matches at least m, up to n x

/ / character class: alternate character

This | where | logo matches either this or where or logo

/ / character class: record character

$1 matches the contents of the first group

Example:

Pattern = / g.. glebind; / / ".": matches any character

Pattern = / g.roomgleswap; / / ". *": matches 0 or any number of characters

Pattern = / g [a murz] * gle/; / / [a murz] *: match any character in a murz

Pattern = / g [^ 0-9] * gle/; / / [^ 0-9] *: match any character other than 0-9

Pattern = / [Amurz] [Amurz] + /; / / [Amurz] +: matches the characters in Amurz one or more times

Pattern = / g\ wroomgleplash; / /\ wband: matches any number of all characters, digits and _

Pattern = / google\ dhammer; / /\ dstrings: match any number of digits

Pattern = /\ D {7,} /; / /\ D {7,}: match at least 7 non-digits

Pattern = / ^ google$/; / / "^": match from beginning; "$": match from end

Var pattern = / 8 (. *) 8 /

Var str = 'This is 8google8'

Str.match (pattern)

Console.log (RegExp.$1); / / get the string content in the first grouping

two。 Greed and inertia

+ +?

???

*?

{n} {n}?

{n,} {n,}?

{n,m} {n,m}?

Var pattern = / [a murz] + /; / / "?": greedy matching is turned off, only the first one is replaced.

Var str = 'abcdefg'

Alert (str.replace (pattern,'xxx')); / / = > xxxdefg

/ / use exec to return an array

Var pattern = / ^ [a murz] +\ s [0-9] {4} $/ I

Var str = 'google 2015'

Alert (pattern.exec (str) [0]); / / returns the entire string = > google 2015

Var pattern = / ^ [amerz] + / I

Var str = 'google 2015'

Alert (pattern.exec (str)); / / returns the matching letter = > google

/ / use special character matching

Var pattern = /\.\ [\ / b\] /

Var str ='.[ / b]'

Alert (pattern.test (str))

/ / use newline mode

Var pattern = / ^\ d+/mg

Var str = '1.baidu\ n2.google\ n3.bing.'

Var result = str.replace (pattern, "#")

Alert (result); / / # .baidu # .Google # .bing

Four commonly used rules

1. Check the zip code

/ / A total of 6 digits, the first digit cannot be 0

Var pattern = / [1-9] [0-9] {5} /

Var str = '224000'

Alert (pattern.test (str))

two。 Check the file package

/ / number + letter + _ +. + zip | rar | gz

Var pattern = / [\ w] +\ .zip | rar | gz/

Var str = '123.zip'

Alert (pattern.test (str))

3. Delete extra spaces

Var pattern = /\ sUnig; / / must be global in order to match all

Var str = '1112222333'

Var result = str.replace (pattern, "")

4. Delete leading and trailing spaces

Var pattern = / ^\ s impulse; / / forced first

Var str = 'goo gle'

Var result = str.replace (pattern, ""); / / remove the leading space

Pattern = /\ s forced tail

Result = result.replace (pattern, ""); / / remove the trailing space

5. Simple email verification

Var pattern = / ^ ([a-zA-Z0-9 _\.\ -] +) @ ([a-zA-Z0-0 _\.\ -] +)\. ([a-zA-Z] {2jue 4}) $/

Var str = 'abc123.com@gmail.com'

Alert (pattern.test (str))

These are all the contents of the article "how to implement regular expressions in JavaScript". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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