Šajā apmācībā jūs uzzināsit par JavaScript regulārajām izteiksmēm (Regex), izmantojot piemērus.
JavaScript A Reģ Serpent Ex pression (RegEx) ir objekts, kas raksturo rakstzīmju secību, ko izmanto, lai definētu meklēšanas modeli. Piemēram,
/ a… s $ /
Iepriekš minētais kods nosaka RegEx modeli. Modelis ir: jebkura piecu burtu virkne, kas sākas ar a
un beidzas ar s
.
Modeli, kas definēts, izmantojot RegEx, var izmantot, lai saskaņotu ar virkni.
Izteiksme | Stīga | Saskaņots? |
---|---|---|
/^a… s$/ | abs | Nav sakritības |
alias | Spēle | |
abyss | Spēle | |
Alias | Nav sakritības | |
An abacus | Nav sakritības |
Izveidojiet RegEx
Regulārā izteiksme JavaScript var izveidot divos veidos.
- Regulāras izteiksmes literāla izmantošana:
regulārā izteiksme sastāv no modeļa, kas ievietots starp slīpsvītrām/
. Piemēram,cost regularExp = /abc/;
/abc/
ir regulāra izteiksme. - Izmantojot
RegExp()
konstruktors funkcija :
Jūs varat arī izveidot regulāru izteiksmi, zvanotRegExp()
konstruktors funkciju. Piemēram,const reguarExp = new RegExp('abc');
Piemēram,
const regex = new RegExp(/^a… s$/); console.log(regex.test('alias')); // true
Iepriekš minētajā piemērā virkne alias
sakrīt ar RegEx modeli /^a… s$/
. Šeit test()
metodi izmanto, lai pārbaudītu, vai virkne atbilst paraugam.
Ir vairākas citas metodes, kuras var izmantot ar JavaScript RegEx. Pirms tos izpētīsim, uzzināsim par pašiem regulārajiem izteicieniem.
Ja jūs jau zināt RegEx pamatus, pārejiet uz JavaScript RegEx metodes.
Norādiet modeli, izmantojot RegEx
Lai norādītu regulāras izteiksmes, tiek izmantotas metarakstzīmes. Iepriekš minētajā piemērā ( /^a… s$/
) ^
un tie $
ir metaraksti.
Meta rakstzīmes
Metahomas ir rakstzīmes, kuras īpašā veidā interpretē RegEx dzinējs. Šeit ir metarakstu saraksts:
(). $ * +? () () |
()
- kvadrātiekavas
Kvadrātiekavās tiek norādīts rakstzīmju kopums, kuru vēlaties saskaņot.
Izteiksme | Stīga | Saskaņots? |
---|---|---|
(abc) | a | 1 mačs |
ac | 2 sērkociņi | |
Hey Jude | Nav sakritības | |
abc de ca | 5 sērkociņi |
Šeit (abc)
būs saskaņot, ja virkne jūs mēģināt saskaņot satur kādu no a
, b
vai c
.
Varat arī norādīt rakstzīmju diapazonu, izmantojot -
iekšējās kvadrātiekavas.
(a-e)
ir tas pats, kas (abcde)
.
(1-4)
ir tas pats, kas (1234)
.
(0-39)
ir tas pats, kas (01239)
.
Jūs varat papildināt (apgriezt) rakstzīmju kopu, ^
kvadrātiekavas sākumā izmantojot simbola simbolu.
(^abc)
nozīmē jebkuru rakstzīmi, izņemot a
, vai b
, vai c
.
(^0-9)
nozīmē jebkuru ciparu bez cipariem.
.
- Periods
Punkts atbilst jebkurai atsevišķai rakstzīmei (izņemot jauno rindu ''
).
Izteiksme | Stīga | Saskaņots? |
---|---|---|
… | a | Nav sakritības |
ac | 1 mačs | |
acd | 1 mačs | |
acde | 2 spēles (satur 4 rakstzīmes) |
^
- Caret
Simbols caret ^
tiek izmantots, lai pārbaudītu, vai virkne sākas ar noteiktu rakstzīmi.
Izteiksme | Stīga | Saskaņots? |
---|---|---|
^a | a | 1 mačs |
abc | 1 mačs | |
bac | Nav sakritības | |
^ab | abc | 1 mačs |
acb | Nav spēles (sākas ar, a bet neseko b ) |
$
- Dolārs
Dolāra simbols $
tiek izmantots, lai pārbaudītu, vai virkne beidzas ar noteiktu rakstzīmi.
Izteiksme | Stīga | Saskaņots? |
---|---|---|
a$ | a | 1 mačs |
formula | 1 mačs | |
cab | Nav sakritības |
*
- Zvaigzne
Zvaigznes simbols *
sakrīt ar nulli vai vairāk tam atstātā raksta.
Izteiksme | Stīga | Saskaņots? |
---|---|---|
ma*n | mn | 1 mačs |
man | 1 mačs | |
mann | 1 mačs | |
main | Nav atbilstības ( a neseko n ) |
|
woman | 1 mačs |
+
- 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() | Meklē atbilstību virknē un aizstāj saskaņoto apakšvirkni ar aizstājošo apakšvirsrakstu. |
split() | Sadaliet virkni apakšvirsmu masīvā. |
1. piemērs: Regulārās izteiksmes
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")
Regulārās izteiksmes karogi
Karodziņi tiek izmantoti ar regulārām izteiksmēm, kas ļauj izmantot dažādas opcijas, piemēram, globālo meklēšanu, reģistrjutīgo meklēšanu utt. Tos var izmantot atsevišķi vai kopā.
Karogi | Apraksts |
---|---|
g | Veic globālu spēli (atrast visas spēles) |
m | Veic daudzrindu spēli |
i | Veic maza un maza rakstura salīdzināšanu |
2. piemērs: Regulārās izteiksmes modifikators
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. piemērs: tālruņa numura pārbaude
// 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);
Rezultāts
Ievadiet numuru XXX-XXX-XXXX: 2343223432 Ievadiet numuru XXX-XXX-XXXX formātā: 234-322-3432 Numurs ir derīgs
4. piemērs: E-pasta adreses pārbaude
// 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);
Rezultāts
Ievadiet e-pastu: hellohello Ievadiet derīgu e-pastu: [email protected] E-pasts ir derīgs.