JavaScript Regex

En este tutorial, aprenderá sobre las expresiones regulares de JavaScript (Regex) con la ayuda de ejemplos.

En JavaScript, un Reg ular Ex pression (RegEx) es un objeto que describe una secuencia de caracteres usado para la definición de un patrón de búsqueda. Por ejemplo,

 / a… s $ /

El código anterior define un patrón RegEx. El patrón es: cualquier cadena de cinco letras que comience con a y termine con s .

Se puede utilizar un patrón definido mediante RegEx para hacer coincidir una cadena.

Expresión Cuerda Emparejado?
/^a… s$/ abs Sin coincidencia
alias Partido
abyss Partido
Alias Sin coincidencia
An abacus Sin coincidencia

Crear una expresión regular

Hay dos formas de crear una expresión regular en JavaScript.

  1. Uso de un literal de expresión regular:
    la expresión regular consta de un patrón encerrado entre barras /. Por ejemplo, 
     cost regularExp = /abc/;
    Aquí /abc/hay una expresión regular.
  2. Usando la RegExp() función constructora :
    también puede crear una expresión regular llamando a la RegExp()función constructora. Por ejemplo, 
     const reguarExp = new RegExp('abc');

Por ejemplo,

 const regex = new RegExp(/^a… s$/); console.log(regex.test('alias')); // true

En el ejemplo anterior, la cadena aliascoincide con el patrón RegEx /^a… s$/. Aquí, el test()método se usa para verificar si la cadena coincide con el patrón.

Hay varios otros métodos disponibles para usar con JavaScript RegEx. Antes de explorarlos, aprendamos sobre las expresiones regulares en sí mismas.

Si ya conoce los conceptos básicos de la expresión regular, vaya a Métodos de expresión regular de JavaScript.

Especificar patrón usando expresiones regulares

Para especificar expresiones regulares, se utilizan metacaracteres. En el ejemplo anterior ( /^a… s$/), ^y $son metacaracteres.

Metacaracteres

Los metacaracteres son caracteres que se interpretan de manera especial mediante un motor RegEx. Aquí hay una lista de metacaracteres:

(). $ * +? () () |

() - Corchetes

Los corchetes especifican un conjunto de caracteres que desea hacer coincidir.

Expresión Cuerda Emparejado?
(abc) a 1 partido
ac 2 partidos
Hey Jude Sin coincidencia
abc de ca 5 partidos

Aquí, (abc)coincidirá si la cadena que está intentando hacer coincidir contiene alguno de los a, bo c.

También puede especificar un rango de caracteres usando -entre corchetes.

(a-e)es lo mismo que (abcde).

(1-4)es lo mismo que (1234).

(0-39)es lo mismo que (01239).

Puede complementar (invertir) el conjunto de caracteres utilizando el ^símbolo de intercalación al comienzo de un corchete.

(^abc) means any character except a or b or c.

(^0-9) means any non-digit character.

. - Period

A period matches any single character (except newline '').

Expression String Matched?
… a No match
ac 1 match
acd 1 match
acde 2 matches (contains 4 characters)

^ - Caret

The caret symbol ^ is used to check if a string starts with a certain character.

Expression String Matched?
^a a 1 match
abc 1 match
bac No match
^ab abc 1 match
acb No match (starts with a but not followed by b)

$ - Dollar

The dollar symbol $ is used to check if a string ends with a certain character.

Expression String Matched?
a$ a 1 match
formula 1 match
cab No match

* - Star

The star symbol * matches zero or more occurrences of the pattern left to it.

Expression String Matched?
ma*n mn 1 match
man 1 match
mann 1 match
main No match (a is not followed by n)
woman 1 match

+ - Plus

The plus symbol + matches one or more occurrences of the pattern left to it.

Expression String Matched?
ma+n mn No match (no a character)
man 1 match
mann 1 match
main No match (a is not followed by n)
woman 1 match

? - Question Mark

The question mark symbol ? matches zero or one occurrence of the pattern left to it.

Expression String Matched?
ma?n mn 1 match
man 1 match
mann No match (more than one n character)
main No match (a is not followed by n)
woman 1 match

() - Braces

Consider this code: (n,m). This means at least n, and at most m repetitions of the pattern left to it.

Expression String Matched?
a(2,3) abc dat No match
abc daat 1 match (at daat)
aabc daaat 2 matches (at aabc and daaat)
aabc daaaat 2 matches (at aabc and daaaat)

Let's try one more example. This RegEx (0-9)(2, 4) matches at least 2 digits but not more than 4 digits.

Expression String Matched?
(0-9)(2,4) ab123csde 1 match (match at ab123csde)
12 and 345673 3 matches (12, 3456, 73)
1 and 2 No match

| - Alternation

Vertical bar | is used for alternation (or operator).

Expression String Matched?
a|b cde No match
ade 1 match (match at ade)
acdbea 3 matches (at acdbea)

Here, a|b match any string that contains either a or b

() - Group

Parentheses () is used to group sub-patterns. For example, (a|b|c)xz match any string that matches either a or b or c followed by xz

Expression String Matched?
(a|b|c)xz ab xz No match
abxz 1 match (match at abxz)
axz cabxz 2 matches (at axzbc cabxz)

- Backslash

Backslash is used to escape various characters including all metacharacters. For example,

$a match if a string contains $ followed by a. Here, $ is not interpreted by a RegEx engine in a special way.

If you are unsure if a character has special meaning or not, you can put in front of it. This makes sure the character is not treated in a special way.

Special Sequences

Special sequences make commonly used patterns easier to write. Here's a list of special sequences:

A - Matches if the specified characters are at the start of a string.

Expression String Matched?
Athe the sun Match
In the sun No match

 - Matches if the specified characters are at the beginning or end of a word.

Expression String Matched?
foo football Match
a football Match
foo a football No match
the foo Match
the afoo test Match
the afootest No match

B - Opposite of . Matches if the specified characters are not at the beginning or end of a word.

Expression String Matched?
Bfoo football No match
a football No match
fooB a football Match
the foo No match
the afoo test No match
the afootest Match

d - Matches any decimal digit. Equivalent to (0-9)

Expression String Matched?
d 12abc3 3 matches (at 12abc3)
JavaScript No match

D - Matches any non-decimal digit. Equivalent to (^0-9)

Expression String Matched?
D 1ab34"50 3 matches (at 1ab34"50)
1345 No match

s - Matches where a string contains any whitespace character. Equivalent to ( fv).

Expression String Matched?
s JavaScript RegEx 1 match
JavaScriptRegEx No match

S - Matches where a string contains any non-whitespace character. Equivalent to (fv).

Expression String Matched?
S a b 2 matches (at a b)
No match

w - Matches any alphanumeric character (digits and alphabets). Equivalent to (a-zA-Z0-9_). By the way, underscore _ is also considered an alphanumeric character.

Expression String Matched?
w 12&": ;c 3 matches (at 12&": ;c)
%"> ! No match

W - Matches any non-alphanumeric character. Equivalent to (^a-zA-Z0-9_)

Expression String Matched?
W 1a2%c 1 match (at 1a2%c)
JavaScript No match

 - Matches if the specified characters are at the end of a string.

Expression String Matched?
JavaScript I like JavaScript 1 match
I like JavaScript Programming No match
JavaScript is fun No match

Tip: To build and test regular expressions, you can use RegEx tester tools such as regex101. This tool not only helps you in creating regular expressions, but it also helps you learn it.

Now you understand the basics of RegEx, let's discuss how to use RegEx in your JavaScript code.

JavaScript Regular Expression Methods

As mentioned above, you can either use RegExp() or regular expression literal to create a RegEx in JavaScript.

 const regex1 = /^ab/; const regex2 = new Regexp('/^ab/');

In JavaScript, you can use regular expressions with RegExp() methods: test() and exec().

There are also some string methods that allow you to pass RegEx as its parameter. They are: match(), replace(), search(), and split().

Method Description
exec() Executes a search for a match in a string and returns an array of information. It returns null on a mismatch.
test() Tests for a match in a string and returns true or false.
match() Returns an array containing all the matches. It returns null on a mismatch.
matchAll() Returns an iterator containing all of the matches.
search() Tests for a match in a string and returns the index of the match. It returns -1 if the search fails.
replace() Busca una coincidencia en una cadena y reemplaza la subcadena coincidente con una subcadena de reemplazo.
split() Divida una cadena en una matriz de subcadenas.

Ejemplo 1: Expresiones regulares

 const string = 'Find me'; const pattern = /me/; // search if the pattern is in string variable const result1 = string.search(pattern); console.log(result1); // 5 // replace the character with another character const string1 = 'Find me'; string1.replace(pattern, 'found you'); // Find found you // splitting strings into array elements const regex1 = /(s,)+/; const result2 = 'Hello world! '.split(regex1); console.log(result2); // ("I", "am", "learning", "JavaScript", "RegEx") // searching the phone number pattern const regex2 = /(d(3))D(d(3))-(d(4))/g; const result3 = regex2.exec('My phone number is: 555 123-4567.'); console.log(result3); // ("555 123-4567", "555", "123", "4567")

Banderas de expresiones regulares

Los indicadores se utilizan con expresiones regulares que permiten varias opciones como búsqueda global, búsqueda que no distingue entre mayúsculas y minúsculas, etc. Se pueden utilizar por separado o juntas.

Banderas Descripción
g Realiza una coincidencia global (encuentra todas las coincidencias)
m Realiza coincidencia multilínea
i Realiza coincidencias que no distinguen entre mayúsculas y minúsculas

Ejemplo 2: Modificador de expresiones regulares

 const string = 'Hello hello hello'; // performing a replacement const result1 = string.replace(/hello/, 'world'); console.log(result1); // Hello world hello // performing global replacement const result2 = string.replace(/hello/g, 'world'); console.log(result2); // Hello world world // performing case-insensitive replacement const result3 = string.replace(/hello/i, 'world'); console.log(result3); // world hello hello // performing global case-insensitive replacement const result4 = string.replace(/hello/gi, 'world'); console.log(result4); // world world world

Ejemplo 3: Validación del número de teléfono

 // program to validate the phone number function validatePhone(num) ( // regex pattern for phone number const re = /^(?((0-9)(3)))?(-. )?((0-9)(3))(-. )?((0-9)(4))$/g; // check if the phone number is valid let result = num.match(re); if (result) ( console.log('The number is valid.'); ) else ( let num = prompt('Enter number in XXX-XXX-XXXX format:'); validatePhone(num); ) ) // take input let number = prompt('Enter a number XXX-XXX-XXXX'); validatePhone(number);

Salida

 Ingrese un número XXX-XXX-XXXX: 2343223432 Ingrese el número en formato XXX-XXX-XXXX: 234-322-3432 El número es válido

Ejemplo 4: Validación de la dirección de correo electrónico

 // program to validate the email address function validateEmail(email) ( // regex pattern for email const re = /S+@S+.S+/g; // check if the email is valid let result = re.test(email); if (result) ( console.log('The email is valid.'); ) else ( let newEmail = prompt('Enter a valid email:'); validateEmail(newEmail); ) ) // take input let email = prompt('Enter an email: '); validateEmail(email);

Salida

 Ingrese un correo electrónico: hellohello Ingrese un correo electrónico válido: [email protected] El correo electrónico es válido.

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