V tej vadnici boste s pomočjo primerov spoznali regularne izraze JavaScript (Regex).
V JavaScripta, A Pravilo pobudami Ex kompresije (regularnim izrazom) je objekt, ki opisuje zaporedje znakov, ki se uporablja za določanje iskalni vzorec. Na primer
/ a… s $ /
Zgornja koda definira vzorec RegEx. Vzorec je: poljuben petčrkovni niz, ki se začne z a
in konča z s
.
Vzorec, definiran z uporabo RegEx, lahko uporabimo za ujemanje z nizom.
Izraz | Vrvica | Ujemajo? |
---|---|---|
/^a… s$/ | abs | Ni zadetka |
alias | Tekma | |
abyss | Tekma | |
Alias | Ni zadetka | |
An abacus | Ni zadetka |
Ustvarite RegEx
V JavaScript lahko na dva načina ustvarite regularni izraz.
- Uporaba dobesednega izraza regularnega izraza:
regularni izraz je sestavljen iz vzorca, zaprtega med poševnicami/
. Na primercost regularExp = /abc/;
/abc/
je regularni izraz. - Uporaba
RegExp()
funkcije konstruktorja :
Regularni izraz lahko ustvarite tudi s klicemRegExp()
funkcije konstruktorja. Na primerconst reguarExp = new RegExp('abc');
Na primer
const regex = new RegExp(/^a… s$/); console.log(regex.test('alias')); // true
V zgornjem primeru se niz alias
ujema z vzorcem RegEx /^a… s$/
. Tu se test()
metoda uporablja za preverjanje, ali se niz ujema z vzorcem.
Na voljo je več drugih metod za uporabo z JavaScript RegEx. Preden jih raziščemo, se naučimo samih regularnih izrazov.
Če že poznate osnove RegEx, pojdite na JavaScript RegEx Methods.
Določite vzorec z uporabo RegEx
Za določitev regularnih izrazov se uporabljajo metaznaki. V zgornjem primeru ( /^a… s$/
) ^
in $
so metaznaki.
MetaCharacters
Metaznaki so znaki, ki jih stroj RegEx razlaga na poseben način. Tu je seznam metaznakov:
(). $ * +? () () |
()
- oglati oklepaji
V oglatih oklepajih je določen nabor znakov, ki se jim želite ujemati.
Izraz | Vrvica | Ujemajo? |
---|---|---|
(abc) | a | 1 tekma |
ac | 2 tekmi | |
Hey Jude | Ni zadetka | |
abc de ca | 5 tekem |
Tu (abc)
se bo ujemalo če niz se potrudiš, da se ujemajo vsebuje katerega koli od a
, b
ali c
.
S pomočjo -
notranjih oglatih oklepajev lahko določite tudi obseg znakov .
(a-e)
je enako kot (abcde)
.
(1-4)
je enako kot (1234)
.
(0-39)
je enako kot (01239)
.
Nabor znakov lahko dopolnite (obrnete) z uporabo ^
znaka za oznako na začetku oglatega oklepaja.
(^abc)
pomeni kateri koli znak, razen a
ali b
ali c
.
(^0-9)
pomeni kateri koli nedimestni znak.
.
- Obdobje
Točka se ujema s katerim koli znakom (razen z novo vrstico ''
).
Izraz | Vrvica | Ujemajo? |
---|---|---|
… | a | Ni zadetka |
ac | 1 tekma | |
acd | 1 tekma | |
acde | 2 ujemanja (vsebuje 4 znake) |
^
- Caret
Simbol kare ^
se uporablja za preverjanje, ali se niz začne z določenim znakom.
Izraz | Vrvica | Ujemajo? |
---|---|---|
^a | a | 1 tekma |
abc | 1 tekma | |
bac | Ni zadetka | |
^ab | abc | 1 tekma |
acb | Ni ujemanja (začne se z, a vendar mu ne sledi b ) |
$
- Dolar
Simbol dolarja $
se uporablja za preverjanje, ali se niz konča z določenim znakom.
Izraz | Vrvica | Ujemajo? |
---|---|---|
a$ | a | 1 tekma |
formula | 1 tekma | |
cab | Ni zadetka |
*
- Zvezda
Simbol zvezde se *
ujema z nič ali več ponovitvami vzorca, ki mu ostane.
Izraz | Vrvica | Ujemajo? |
---|---|---|
ma*n | mn | 1 tekma |
man | 1 tekma | |
mann | 1 tekma | |
main | Ni ujemanja ( a ne sledi n ) |
|
woman | 1 tekma |
+
- 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() | Išče ujemanje v nizu in nadomesti ujemajoč se podniz z nadomestnim podnizom. |
split() | Prekinite niz v niz podnizov. |
Primer 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 z regularnim izrazom
Zastave se uporabljajo z regularnimi izrazi, ki omogočajo različne možnosti, kot so globalno iskanje, iskanje brez občutkov na črke itd. Uporabljajo se lahko ločeno ali skupaj.
Zastave | Opis |
---|---|
g | Izvede globalno ujemanje (poišči vsa ujemanja) |
m | Izvaja večvrstno ujemanje |
i | Izvaja ujemanje med velikimi in malimi črkami |
Primer 2: Modifikator regularnega 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
3. primer: preverjanje veljavnosti telefonske številke
// 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);
Izhod
Vnesite številko XXX-XXX-XXXX: 2343223432 Vnesite številko v obliki XXX-XXX-XXXX: 234-322-3432 Številka je veljavna
Primer 4: Preverjanje e-poštnega naslova
// 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);
Izhod
Vnesite e-poštni naslov: hellohello Vnesite veljaven e-poštni naslov: [email protected] E-poštni naslov je veljaven.