Selles õpetuses saate näidete abil õppida JavaScripti regulaaravaldisi (Regex).
JavaScript, et Reg Ular Ex pression (RegEx) on objekt, mis kirjeldab tähemärkide jada määratlemisel kasutatavate otsing muster. Näiteks,
/ a… s $ /
Ülaltoodud kood määratleb RegExi mustri. Muster on: mis tahes viietäheline string, mis algab a
ja lõpeb tähega s
.
RegEx abil määratletud mustrit saab kasutada stringiga sobitamiseks.
Väljendus | String | Sobinud? |
---|---|---|
/^a… s$/ | abs | Vastet pole |
alias | Matš | |
abyss | Matš | |
Alias | Vastet pole | |
An abacus | Vastet pole |
Looge RegEx
Regulaaravaldise saab JavaScripti luua kahel viisil.
- Regulaaravaldise literaali kasutamine:
Regulaarne avaldis koosneb kaldkriipsude vahele suletud mustrist/
. Näiteks,cost regularExp = /abc/;
/abc/
on regulaarne väljend. - Kasutades
RegExp()
ehitaja funktsiooni :
Saate luua ka regulaaravaldise helistadesRegExp()
ehitaja funktsiooni. Näiteks,const reguarExp = new RegExp('abc');
Näiteks,
const regex = new RegExp(/^a… s$/); console.log(regex.test('alias')); // true
Ülalolevas näites alias
sobib string RegEx-mustriga /^a… s$/
. Siin kontrollitakse test()
meetodit, kas string sobib mustriga.
JavaScripti RegExiga on saadaval veel mitu meetodit. Enne nende uurimist tutvume regulaaravaldistega ise.
Kui teate juba RegExi põhitõdesid, minge JavaScripti RegExi meetodite juurde.
Määrake muster RegExi abil
Regulaaravaldiste täpsustamiseks kasutatakse metamärke. Ülaltoodud näites ( /^a… s$/
) ^
ja $
on metamärgid.
MetaMärgid
Metamärgid on tähemärgid, mida RegExi mootor tõlgendab erilisel viisil. Siin on metamärkide loend:
(). $ * +? () () |
()
- Nurksulud
Nurksulgudes määratakse märkide komplekt, mida soovite sobitada.
Väljendus | String | Sobinud? |
---|---|---|
(abc) | a | 1 matš |
ac | 2 vastet | |
Hey Jude | Vastet pole | |
abc de ca | 5 vastet |
Siin (abc)
sobib kui string püüad sobitada sisaldab ükskõik a
, b
või c
.
Samuti saate -
nurksulgudes sisestada märkide vahemiku.
(a-e)
on sama mis (abcde)
.
(1-4)
on sama mis (1234)
.
(0-39)
on sama mis (01239)
.
Märgistikku saab täiendada (ümber pöörata), kasutades ^
nurksulgude alguses sümbolit sümbol.
(^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() | Otsib stringis vastet ja asendab sobitatud alamstringi asendava alamstringiga. |
split() | Katkesta string alamstringide massiiviks. |
Näide 1: Regulaaravaldised
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")
Regulaaravaldise lipud
Lippe kasutatakse regulaarsete väljenditega, mis võimaldavad mitmesuguseid valikuid, nagu globaalne otsing, suurtähteta otsing jne. Neid saab kasutada eraldi või koos.
Lipud | Kirjeldus |
---|---|
g | Sooritab globaalse vaste (leia kõik vasted) |
m | Sooritab mitmerealise mängu |
i | Teostab suurtähteta tundlikkuse sobitamise |
Näide 2: regulaaravaldise modifikaator
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
Näide 3: telefoninumbri kinnitamine
// 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);
Väljund
Sisestage number XXX-XXX-XXXX: 2343223432 Sisestage number vormingus XXX-XXX-XXXX: 234-322-3432
Näide 4: e-posti aadressi kinnitamine
// 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);
Väljund
Sisestage e-posti aadress: hellohello Sisestage kehtiv e-posti aadress: [email protected] E-posti aadress on kehtiv.