Dalam tutorial ini, anda akan belajar mengenai ungkapan biasa JavaScript (Regex) dengan bantuan contoh.
Dalam JavaScript, Reg ular Ex pression (RegEx) adalah objek yang menggambarkan urutan watak yang digunakan untuk menentukan pola carian. Sebagai contoh,
/ a… s $ /
Kod di atas menentukan corak RegEx. Coraknya ialah: sebarang rentetan lima huruf yang bermula dengan a
dan diakhiri dengan s
.
Pola yang ditentukan menggunakan RegEx dapat digunakan untuk memadankan tali.
Ungkapan | Tali | Sesuai? |
---|---|---|
/^a… s$/ | abs | Tidak setanding |
alias | Padankan | |
abyss | Padankan | |
Alias | Tidak setanding | |
An abacus | Tidak setanding |
Buat RegEx
Terdapat dua cara untuk membuat ungkapan biasa dalam JavaScript.
- Menggunakan literal ungkapan biasa:
Ungkapan biasa terdiri daripada corak yang dilekatkan di antara garis miring/
. Sebagai contoh,cost regularExp = /abc/;
/abc/
adalah ungkapan biasa. - Menggunakan
RegExp()
fungsi konstruktor :
Anda juga dapat membuat ungkapan biasa dengan memanggilRegExp()
fungsi konstruktor. Sebagai contoh,const reguarExp = new RegExp('abc');
Sebagai contoh,
const regex = new RegExp(/^a… s$/); console.log(regex.test('alias')); // true
Dalam contoh di atas, rentetan alias
sesuai dengan corak RegEx /^a… s$/
. Di sini, test()
kaedah ini digunakan untuk memeriksa apakah rentetan itu sesuai dengan corak.
Terdapat beberapa kaedah lain yang tersedia untuk digunakan dengan JavaScript RegEx. Sebelum kita menerokainya, mari kita pelajari sendiri ungkapan biasa.
Sekiranya anda sudah mengetahui asas-asas RegEx, lompat ke Kaedah RegEx JavaScript.
Tentukan Corak Menggunakan RegEx
Untuk menentukan ungkapan biasa, metacharacters digunakan. Dalam contoh di atas ( /^a… s$/
), ^
dan $
merupakan metakarakter.
Watak Meta
Metacharacters adalah watak yang ditafsirkan dengan cara khas oleh mesin RegEx. Berikut adalah senarai watak metakarakter:
(). $ * +? () () |
()
- Dalam kurungan
Tanda kurung persegi menetapkan sekumpulan watak yang ingin anda padankan.
Ungkapan | Tali | Sesuai? |
---|---|---|
(abc) | a | 1 perlawanan |
ac | 2 perlawanan | |
Hey Jude | Tidak setanding | |
abc de ca | 5 perlawanan |
Di sini, (abc)
akan sepadan jika rentetan yang anda cuba untuk perlawanan mengandungi mana-mana daripada a
, b
atau c
.
Anda juga boleh menentukan pelbagai watak menggunakan -
tanda kurung dalam.
(a-e)
sama dengan (abcde)
.
(1-4)
sama dengan (1234)
.
(0-39)
sama dengan (01239)
.
Anda boleh melengkapkan (membalikkan) set watak dengan menggunakan ^
simbol karet pada permulaan kurungan persegi.
(^abc)
bermaksud apa-apa watak kecuali a
atau b
atau c
.
(^0-9)
bermaksud sebarang aksara bukan digit.
.
- Tempoh
Tempoh sepadan dengan mana-mana watak tunggal (kecuali garis baru ''
)
Ungkapan | Tali | Sesuai? |
---|---|---|
… | a | Tidak setanding |
ac | 1 perlawanan | |
acd | 1 perlawanan | |
acde | 2 perlawanan (mengandungi 4 watak) |
^
- Caret
Simbol karet ^
digunakan untuk memeriksa apakah rentetan bermula dengan watak tertentu.
Ungkapan | Tali | Sesuai? |
---|---|---|
^a | a | 1 perlawanan |
abc | 1 perlawanan | |
bac | Tidak setanding | |
^ab | abc | 1 perlawanan |
acb | Tiada perlawanan (bermula dengan a tetapi tidak diikuti b ) |
$
- Dolar
Simbol dolar $
digunakan untuk memeriksa apakah rentetan berakhir dengan watak tertentu.
Ungkapan | Tali | Sesuai? |
---|---|---|
a$ | a | 1 perlawanan |
formula | 1 perlawanan | |
cab | Tidak setanding |
*
- Bintang
Simbol bintang *
sepadan dengan sifar atau lebih banyak corak yang tersisa padanya.
Ungkapan | Tali | Sesuai? |
---|---|---|
ma*n | mn | 1 perlawanan |
man | 1 perlawanan | |
mann | 1 perlawanan | |
main | Tiada perlawanan ( a tidak diikuti oleh n ) |
|
woman | 1 perlawanan |
+
- Tambahan
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() | Mencari pertandingan dalam rentetan dan menggantikan substring yang dipadankan dengan substring pengganti. |
split() | Pecahkan rentetan ke dalam rangkaian substring. |
Contoh 1: Ungkapan Biasa
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")
Bendera Ekspresi Biasa
Bendera digunakan dengan ungkapan biasa yang membolehkan pelbagai pilihan seperti carian global, carian tidak sensitif huruf, dll. Mereka boleh digunakan secara berasingan atau bersama.
Bendera | Penerangan |
---|---|
g | Melakukan pertandingan global (cari semua perlawanan) |
m | Melakukan pertandingan multiline |
i | Melakukan pemadanan tidak peka huruf besar-kecil |
Contoh 2: Pengubah Ekspresi Biasa
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
Contoh 3: Mengesahkan Nombor Telefon
// 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);
Pengeluaran
Masukkan nombor XXX-XXX-XXXX: 2343223432 Masukkan nombor dalam format XXX-XXX-XXXX: 234-322-3432 Nombor itu sah
Contoh 4: Mengesahkan Alamat E-mel
// 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);
Pengeluaran
Masukkan e-mel: hellohello Masukkan e-mel yang sah: [email protected] E-mel tersebut sah.