Advanced Regex With Modern Javascript Complete  Guide
Tags: javascript, es6, reactnative, webdev
Published: 2020-02-16 08:29:45

## What is Regex?
Usually called with **Regular Expression** , **Regexp**, or **Regex.**  Regex is a string of text that allows you to create patterns that help match, locate, and manage text.

Regular expressions are a generalized way to match patterns with sequences of characters. It is used in every programming language like C++, Java, Python, Javascript, etc.

Why do we need to use Regex, ok before Regex is very applicable in Front End and Back End.

**Regex** is useful for filtering text, this is very useful because by using Regex we can choose what characters can enter our server and with regex, we can also filter out a file extension and many more. Ok for more convenience let's do it in this tutorial.

Ok in the introduction in this tutorial we will implement regex using modern javascript using ES6 +.

Ok Before starting this tutorial you can invite your pet like your cat or dog. To walk on your keyboard. *LOL.*


**1. Regex For Number**

 ```javascript

const regNumber = /^\d*(\.\d+)?$/
const result = '123'.match(regNumber)       // true
if (result) {
    console.log('Match')
} else {
    console.log('Not Match')
}


```


**2. Regex For Match Lowercase**

 ```javascript

const regexStringSensitive = /[a-z]/g
const result = 'HELLO'.match(regexStringSensitive)
if (result) {
    console.log('True')
} else {
    console.log('False')
}

```



**3. Regex For Match Email**

 ```javascript

const regexEmail = /^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/
const result = 'helo@gmail.com'.match(regexEmail)
if (result) {
    console.log('Email is Match')
} else {
    console.log('Not Match')
}

```


**4. Regex For Match Some String**

 ```javascript

const regexMatchString = /(abc|def)[0-9]{8,11}/
const result = 'abc234832748374asdf7943278934haskhjd'.match(regexMatchString)  //if match abc234832748374 it will true
if (result) {
    console.log('Match')
} else {
    console.log('Not Match')
}

```

**5. Regex For Match Multi-Word**

 ```javascript

const regexMatchLove = /\LOVE|\bLie/
const result = 'I LOVE YOU AND I NOT LIE'.match(regexMatchLove)  // Match with word LOVE and LIE
if (result) {
    console.log('Match Word')
} else {
    console.log('Not Match')
}

```


**6. Regex For Match File Extensions**

 ```javascript

const regexFileName = /\.(gif|jpg|jpeg|tiff|png)$/i
const result = 'helo.jpg'.match(regexFileName)  // match with filename gif|jpg|jpeg|tiff|png
if (result) {
    console.log('Match File')
} else {
    console.log('Not Match')
}

```

**7. Regex Min Max**

 ```javascript

const regexMinMax = /^.{8,20}$/
const result = 'helo.jpg 123'.match(regexMinMax)   //min 8 max 20
if (result) {
    console.log('Recomended Password')
} else {
    console.log('Not Recomended Password')
}

```

**8. Regex For Special Character**

 ```javascript

const regexSpecialCharacter = /[\!\@\#\$\%\^\&\*\)\(\+\=\.\<\>\{\}\[\]\:\;\'\"\|\~\`\_\-]/g
const result = '*( Helo {k. ='.match(regexSpecialCharacter)
if (result) {
    console.log('Contain Special Character')
} else {
    console.log('Not Contain Special Character')
}

```


#Reference for Regex

```
Any character except [\^$.|?*+()	Literal character
\ followed by any of [\^$.|?*+(){}	Backslash escapes a metacharacter
.	Any character
|	Alternation
\|	Alternation
?	Greedy quantifier
\?	Greedy quantifier
??	Lazy quantifier
?+	Possessive quantifier
*	Greedy quantifier
*?	Lazy quantifier
*+	Possessive quantifier
+	Greedy quantifier
\+	Greedy quantifier
+?	Lazy quantifier
++	Possessive quantifier
{ and }	Literal curly braces
{n} where n is an integer >= 1	Fixed quantifier
{n,m} where n >= 0 and m >= n	Greedy quantifier
{n,} where n >= 0	Greedy quantifier
{,m} where m >= 1	Greedy quantifier
\{n\} where n is an integer >= 1	Fixed quantifier
\{n,m\} where n >= 0 and m >= n	Greedy quantifier
\{n,\} where n >= 0	Greedy quantifier
\{,m\} where m >= 1	Greedy quantifier
{n,m}? where n >= 0 and m >= n	Lazy quantifier
{n,}? where n >= 0	Lazy quantifier
{,m}? where m >= 1	Lazy quantifier
{n,m}+ where n >= 0 and m >= n	Possessive quantifier
{n,}+ where n >= 0	Possessive quantifier
^	String anchor
^	Line anchor
$	String anchor
$	Line anchor
\a	Character escape
\A	String anchor
\A	Attempt anchor
\b	Word boundary
\b	Backspace character
\B	Word non-boundary
\B	Backslash character
\c	XML shorthand
\ca through \cz	Control character escape
\cA through \cZ	Control character escape
\C	XML shorthand
\d	Digits shorthand
\D	Non-digits shorthand
\e	Escape character
\f	Form feed character
\g{name}	Named backreference
\g-1, \g-2, etc.	Relative Backreference
\g{-1}, \g{-2}, etc.	Relative Backreference
\g1 through \g99	Backreference
\g{1} through \g{99}	Backreference
\g<name> where “name” is the name of a capturing group	Named subroutine call
\g<name> where “name” is the name of a capturing group	Named backreference
\g'name' where “name” is the name of a capturing group	Named subroutine call
\g'name' where “name” is the name of a capturing group	Named backreference
\g<0>	Recursion
\g'0'	Recursion
\g<1> where 1 is the number of a capturing group	Subroutine call
\g<1> where 1 is the number of a capturing group	Backreference
\g'1' where 1 is the number of a capturing group	Subroutine call
\g'1' where 1 is the number of a capturing group	Backreference
\g<-1> where -1 is a negative integer	Relative subroutine call
\g<-1> where -1 is a negative integer	Relative backreference
\g'-1' where -1 is a negative integer	Relative subroutine call
\g'-1' where -1 is a negative integer	Relative backreference
\g<+1> where +1 is a positive integer	Forward subroutine call
\g'+1' where +1 is a positive integer	Forward subroutine call
\G	Attempt anchor
\G	Match anchor
\h	Hexadecimal digit shorthand
\h	Horizontal whitespace shorthand
\H	Non-hexadecimal digit shorthand
\H	Non-horizontal whitespace shorthand
\i	XML shorthand
\I	XML shorthand
\k<name>	Named backreference
\k'name' through \k'99'	Named backreference
\k{name}	Named backreference
\k<1> through \k<99>	Backreference
\k'1' through \k'99'	Backreference
\k<-1>, \k<-2>, etc.	Relative Backreference
\k'-1', \k'-2', etc.	Relative Backreference
\K	Keep text out of the regex match
\l	Lowercase shorthand
\L	Non-lowercase shorthand
\m	Tcl start of word boundary
\M	Tcl end of word boundary
\n	Line feed character
\N	Not a line break
Literal CRLF, LF, or CR line break	Line break
\o{7777} where 7777 is any octal number	Octal escape
\pL where L is a Unicode category	Unicode category
\PL where L is a Unicode category	Unicode category
\p{L} where L is a Unicode category	Unicode category
\p{IsL} where L is a Unicode category	Unicode category
\p{Category}	Unicode category
\p{IsCategory}	Unicode category
\p{Script}	Unicode script
\p{IsScript}	Unicode script
\p{Block}	Unicode block
\p{InBlock}	Unicode block
\p{IsBlock}	Unicode block
\P{Property}	Negated Unicode property
\p{^Property}	Negated Unicode property
\P{^Property}	Unicode property
\Q…\E	Escape sequence
\r	Carriage return character
\R	Line break
\s	Whitespace shorthand
\S	Non-whitespace shorthand
\t	Tab character
\u	Uppercase shorthand
\uFFFF where FFFF are 4 hexadecimal digits	Unicode code point
\u{FFFF} where FFFF are 1 to 4 hexadecimal digits	Unicode code point
\U	Non-uppercase shorthand
\v	Vertical tab character
\v	Vertical whitespace shorthand
\V	Non-vertical whitespace shorthand
\w	Word character shorthand
\W	Non-word character shorthand
\xFF where FF are 2 hexadecimal digits	Hexadecimal escape
\xFFFF where FFFF are 4 hexadecimal digits	Unicode code point
\x{FFFF} where FFFF are 1 to 4 hexadecimal digits	Unicode code point
\X	Unicode grapheme
\y	Tcl word boundary
\Y	Tcl word non-boundary
\Z	String anchor
\z	String anchor
\0	NULL escape
\1 through \7	Octal escape
\1 through \9	Backreference
\10 through \77	Octal escape
\10 through \99	Backreference
\100 through \377	Octal escape
\01 through \0377	Octal escape
\‘	String anchor
\‘	Attempt anchor
\'	String anchor
\<	GNU word boundary
\>	GNU word boundary
[[:<:]]	POSIX word boundary
[[:>:]]	POSIX word boundary
(regex)	Capturing group
\(regex\)	Capturing group
(?:regex)	Non-capturing group
(?<name>regex)	Named capturing group
(?'name'regex)	Named capturing group
(?#comment)	Comment
(?|regex)	Branch reset group
(?>regex)	Atomic group
(?=regex)	Positive lookahead
(?!regex)	Negative lookahead
(?<=regex)	Positive lookbehind
(?<!regex)	Negative lookbehind
(?(?=regex)then|else) where (?=regex) is any valid lookaround and then and else are any valid regexes	Lookaround conditional
(?(regex)then|else) where regex, then, and else are any valid regexes and regex is not the name of a capturing group	Implicit lookahead conditional
(?(name)then|else) where name is the name of a capturing group and then and else are any valid regexes	Named conditional
(?(<name>)then|else) where name is the name of a capturing group and then and else are any valid regexes	Named conditional
(?('name')then|else) where name is the name of a capturing group and then and else are any valid regexes	Named conditional
(?(1)then|else) where 1 is the number of a capturing group and then and else are any valid regexes	Conditional
(?(-1)then|else) where -1 is a negative integer and then and else are any valid regexes	Relative conditional
(?(+1)then|else) where +1 is a positive integer and then and else are any valid regexes	Forward conditional
(?(+1)then|else) where 1 is the number of a capturing group and then and else are any valid regexes	Conditional
(?<capture-subtract>regex) where “capture” and “subtract” are group names and “regex” is any regex	Balancing group
(?'capture-subtract'regex) where “capture” and “subtract” are group names and “regex” is any regex	Balancing group
(?&name) where “name” is the name of a capturing group	Named subroutine call
(?(DEFINE)regex) where “regex” is any regex	Subroutine definitions
(?P<name>regex)	Named capturing group
(?P=name)	Named backreference
(?P=1) through (?P=99)	Backreference
(?P>name) where “name” is the name of a capturing group	Named subroutine call
(?R)	Recursion
(?0)	Recursion
(?1) where 1 is the number of a capturing group	Subroutine call
(?-1) where -1 is a negative integer	Relative subroutine call
(?+1) where +1 is a positive integer	Forward subroutine call

```

Now that above is the Regular Expression that is most widely used by programmers to filter characters. Please develop it with your needs. It may be useful.


source: *www.regular-expressions.info*