JavaScript regularni izraz

U ovom ćete tutorijalu uz primjere naučiti o JavaScript regularnim izrazima (Regex).

U JavaScript-u, Reg ular Ex Pression (RegEx) je objekt koji opisuje slijed znakova koji se koriste za definiranje uzorka pretraživanja. Na primjer,

 / a… s $ /

Gornji kod definira RegEx obrazac. Uzorak je: bilo koji niz od pet slova koji započinje a i završava s s .

Uzorak definiran pomoću RegEx-a može se koristiti za podudaranje sa nizom.

Izraz Niz Podudarno?
/^a… s$/ abs Nema podudaranja
alias Podudarnost
abyss Podudarnost
Alias Nema podudaranja
An abacus Nema podudaranja

Stvorite RegEx

Postoje dva načina na koja možete stvoriti regularni izraz u JavaScript-u.

  1. Upotreba doslovca regularnog izraza:
    Regularni izraz sastoji se od uzorka zatvorenog između kose crte /. Na primjer, 
     cost regularExp = /abc/;
    Evo /abc/regularnog izraza.
  2. Korištenje funkcije RegExp() konstruktora :
    Također možete stvoriti regularni izraz pozivanjem funkcije RegExp()konstruktora. Na primjer, 
     const reguarExp = new RegExp('abc');

Na primjer,

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

U gornjem primjeru niz se aliaspodudara s uzorkom RegEx /^a… s$/. Ovdje se test()metoda koristi za provjeru odgovara li niz uzorku.

Postoji nekoliko drugih metoda dostupnih za upotrebu s JavaScript RegExom. Prije nego što ih istražimo, naučimo same regularne izraze.

Ako već znate osnove RegExa, prijeđite na JavaScript RegEx metode.

Navedite obrazac pomoću RegEx-a

Za specificiranje regularnih izraza koriste se metaznakovi. U gornjem primjeru ( /^a… s$/) ^i $su metaznakovi.

MetaCharacters

Metaznakovi su znakovi koje RegExov mehanizam tumači na poseban način. Evo popisa metaznaka:

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

() - Uglate zagrade

Uglate zagrade određuju skup znakova s ​​kojima se želite podudarati.

Izraz Niz Podudarno?
(abc) a 1 utakmica
ac 2 utakmice
Hey Jude Nema podudaranja
abc de ca 5 utakmica

Ovdje (abc)će odgovarati ako niz pokušavate uskladiti sadrži bilo koji od a, bili c.

Također možete odrediti raspon znakova pomoću -unutarstih zagrada.

(a-e)je isto što i (abcde).

(1-4)je isto što i (1234).

(0-39)je isto što i (01239).

Možete nadopuniti (invertirati) skup znakova pomoću ^simbola znaka na početku uglate zagrade.

(^abc)označava bilo koji znak osim aili bili c.

(^0-9) znači bilo koji ne-znamenkasti znak.

. - Razdoblje

Točka se podudara s bilo kojim pojedinačnim znakom (osim novog retka '').

Izraz Niz Podudarno?
… a Nema podudaranja
ac 1 utakmica
acd 1 utakmica
acde 2 podudaranja (sadrži 4 znaka)

^ - Caret

Simbol karete ^koristi se za provjeru započinje li niz određenim znakom.

Izraz Niz Podudarno?
^a a 1 utakmica
abc 1 utakmica
bac Nema podudaranja
^ab abc 1 utakmica
acb Nema podudaranja (započinje, aali ne slijedi b)

$ - Dolar

Simbol dolara $koristi se za provjeru završava li niz određenim znakom.

Izraz Niz Podudarno?
a$ a 1 utakmica
formula 1 utakmica
cab Nema podudaranja

* - Zvijezda

Simbol zvijezde *podudara se s nula ili više pojavljivanja uzorka koji mu je ostavljen.

Izraz Niz Podudarno?
ma*n mn 1 utakmica
man 1 utakmica
mann 1 utakmica
main Nema podudaranja ( ane slijedi ga n)
woman 1 utakmica

+ - 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() Traži podudaranje u nizu i zamjenjuje podudarnost koja se podudara s zamjenskim podnizom.
split() Razbijte niz u niz podnizova.

Primjer 1: Regularni izrazi

 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")

Zastave redovnog izraza

Zastave se koriste s regularnim izrazima koji omogućuju razne opcije poput globalnog pretraživanja, pretraživanja bez velikih i malih slova itd. Mogu se koristiti zasebno ili zajedno.

Zastave Opis
g Izvodi globalno podudaranje (pronađi sva podudaranja)
m Izvodi višelinijsko podudaranje
i Izvodi podudaranje bez velikih i malih slova

Primjer 2: Modifikator regularnog izraza

 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

Primjer 3: Provjera valjanosti telefonskog broja

 // 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);

Izlaz

 Unesite broj XXX-XXX-XXXX: 2343223432 Unesite broj u formatu XXX-XXX-XXXX: 234-322-3432 Broj je važeći

Primjer 4: Provjera adrese e-pošte

 // 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);

Izlaz

 Unesite e-adresu: hellohello Unesite valjanu e-adresu: [email protected] E-adresa je valjana.

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