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Regular Expression Cheatsheet

Creating regex

Regular expressions are patterns used to match character combinations in strings.

Literal syntax

const re = /hello/;
re.test("hello world"); // true

RegExp constructor

const re = new RegExp("hello", "i"); // same as /hello/i
re.test("HELLO world"); // true

Flags

Flag	Description
`g`	Global search.
`i`	Case-insensitive.
`m`	Multiline mode.
`s`	Dotall mode (`.` matches newlines).
`u`	Unicode mode.
`y`	Sticky mode.

`g`: Global

Finds all matches instead of stopping at the first.

"hello world".match(/o/g); // ["o", "o"]
"a1b2c3".replace(/\d/g, "x"); // "axbxcx"

`i`: Case-insensitive

Matches letters regardless of case.

/hello/i.test("HELLO"); // true
"Hello World".match(/hello/i); // ["Hello"]

`m`: Multiline

Changes ^ and $ to match the start and end of each line instead of the whole string.

const text = "hello\nworld";
/^world$/m.test(text); // true

`s`: Dotall

Makes . match newline characters too.

const html = "<div>\n  hello\n</div>";
/<div>.*<\/div>/s.test(html); // true

`u`: Unicode

Enables full Unicode matching and lets you use \u{} escapes and Unicode property escapes.

/\u{1F600}/u.test("😀"); // true
/\p{Emoji}/u.test("😀"); // true

`y`: Sticky

Matches only from the lastIndex position and does not search further.

const re = /\d+/y;
re.lastIndex = 2;
"ab12cd".match(re); // ["12"]
 
re.lastIndex = 0;
"ab12cd".match(re); // null

Character classes

Pattern	Matches
`.`	Any character except newline (Any character with `s` flag).
`[a-z]`	Any character in the range.
`\d`	Any digit (`0-9`).
`\D`	Any non-digit.
`\w`	Any word character (`a-z`, `A-Z`, `0-9`, `_`).
`\W`	Any non-word character.
`\s`	Any whitespace character.
`\S`	Any non-whitespace character.
`[abc]`	Any character in the set.
`[^abc]`	Any character not in the set.

`.`: Any character

"a".match(/./); // ["a"]
"abc".match(/./g); // ["a", "b", "c"]

`[a-z]`: Character range

"Hello".match(/[a-z]/); // ["e"]
"HELLO".match(/[a-z]/); // null

`\d`: Digit

"abc123".match(/\d+/); // ["123"]
"Room 42".match(/\d+/); // ["42"]

`\D`: Non-digit

"abc123".match(/\D+/); // ["abc"]
"2024!".match(/\D/); // ["!"]

`\w`: Word character

"hello_world".match(/\w+/); // ["hello_world"]
"user_123".match(/\w+/); // ["user_123"]

`\W`: Non-word character

"hello world".match(/\W/); // [" "]
"a@b".match(/\W/); // ["@"]

`\s`: Whitespace

"a b".match(/\s/); // [" "]
"a\tb".match(/\s/); // ["\t"]

`\S`: Non-whitespace

" a".match(/\S/); // ["a"]
"  hi".match(/\S+/); // ["hi"]

`[abc]`: Character set

"cat".match(/[aeiou]/); // ["a"]
"sky".match(/[aeiou]/); // null

`[^abc]`: Negated character set

"cat".match(/[^aeiou]/); // ["c"]
"aei".match(/[^aeiou]/); // null

Quantifiers

Pattern	Meaning
`*`	Zero or more.
`+`	One or more.
`?`	Zero or one.
`{n}`	Exactly `n` times.
`{n,}`	At least `n` times.
`{n,m}`	Between `n` and `m` times.

`*`: Zero or more

"aaab".match(/a*/); // ["aaa"]
"b".match(/a*/); // [""]

`+`: One or more

"aaab".match(/a+/); // ["aaa"]
"b".match(/a+/); // null

`?`: Zero or one

"color".match(/colou?r/); // ["color"]
"colour".match(/colou?r/); // ["colour"]

`{n}`: Exactly n times

"123".match(/\d{3}/); // ["123"]
"12".match(/\d{3}/); // null

`{n,}`: At least n times

"12345".match(/\d{3,}/); // ["12345"]
"12".match(/\d{3,}/); // null

`{n,m}`: Between n and m times

"1234".match(/\d{2,4}/); // ["1234"]
"1".match(/\d{2,4}/); // null

Anchors

Pattern	Matches
`^`	Start of string (or line in `m` mode).
`$`	End of string (or line in `m` mode).
`\b`	Word boundary.
`\B`	Non-word boundary.

`^`: Start of string

/^hello/.test("hello world"); // true
/^world/.test("hello world"); // false

`$`: End of string

/world$/.test("hello world"); // true
/hello$/.test("hello world"); // false

`\b`: Word boundary

/\bworld\b/.test("hello world"); // true
/\bworld\b/.test("helloworld"); // false

`\B`: Non-word boundary

/\Bworld\B/.test("helloworld"); // true
/\Bworld\B/.test("hello world"); // false

Groups

Pattern	Description
`(...)`	Capturing group. Stores the matched text for later use.
`(?:...)`	Non-capturing group. Groups without storing.
`(?<name>...)`	Named capturing group. Stores the match under a name.

Capturing group

const match = "2024-07-12".match(/(\d{4})-(\d{2})-(\d{2})/);
match[0]; // "2024-07-12"
match[1]; // "2024"
match[2]; // "07"
match[3]; // "12"

Non-capturing group

const match = "foo".match(/(?:foo|bar)/); // ["foo"]
match[0]; // "foo"

Named capturing group

const match = "2024-07-12".match(
  /(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})/,
);
match.groups.year; // "2024"

Lookarounds

Pattern	Description
`(?=...)`	Positive lookahead.
`(?!...)`	Negative lookahead.
`(?<=...)`	Positive lookbehind.
`(?<!...)`	Negative lookbehind.

`(?=...)`: Positive lookahead

Matches a group only if followed by another pattern.

/\d+(?=px)/.exec("100px"); // ["100"]
/\d+(?=px)/.exec("100em"); // null

`(?!...)`: Negative lookahead

Matches a group only if not followed by another pattern.

/\d+(?!px)/.exec("100em"); // ["100"]
/\d+(?!px)/.exec("100px"); // null

`(?<=...)`: Positive lookbehind

Matches a group only if preceded by another pattern.

/(?<=\$)\d+/.exec("Price: $42"); // ["42"]
/(?<=\$)\d+/.exec("Price: 42"); // null

`(?<!...)`: Negative lookbehind

Matches a group only if not preceded by another pattern.

/(?<!\$)\d+/.exec("Price: 42"); // ["42"]
/(?<!\$)\d+/.exec("Price: $42"); // null

JavaScript regex methods

`.test()`

Returns true if the pattern matches.

/hello/.test("hello world"); // true

`.match()`

Returns an array of matches.

"abc123".match(/\d+/); // ["123"]
"a1b2c3".match(/\d/g); // ["1", "2", "3"]

`.matchAll()`

Returns an iterator of all matches with capture groups.

const matches = "a1b2".matchAll(/[a-z](\d)/g);
for (const match of matches) {
  console.log(match[0], match[1]);
}

`.replace()`

Replaces the first match, or all matches with the g flag.

"hello world".replace(/world/, "JS"); // "hello JS"
"a b c".replace(/\s/g, "-"); // "a-b-c"

`.replaceAll()`

Replaces all matches without needing the g flag.

"a b c".replaceAll(" ", "-"); // "a-b-c"

`.search()`

Returns the index of the first match, or -1.

"hello world".search(/world/); // 6

`.split()`

Splits a string using a regex.

"a,b;c".split(/[,;]/); // ["a", "b", "c"]

❤ Like

🔖 Save

🔗 Share

@thedevspaceio

Regular Expression Cheatsheet

Creating regex

Regular expressions are patterns used to match character combinations in strings.

Literal syntax

const re = /hello/;
re.test("hello world"); // true

RegExp constructor

const re = new RegExp("hello", "i"); // same as /hello/i
re.test("HELLO world"); // true

Flags

Flag	Description
`g`	Global search.
`i`	Case-insensitive.
`m`	Multiline mode.
`s`	Dotall mode (`.` matches newlines).
`u`	Unicode mode.
`y`	Sticky mode.

`g`: Global

Finds all matches instead of stopping at the first.

"hello world".match(/o/g); // ["o", "o"]
"a1b2c3".replace(/\d/g, "x"); // "axbxcx"

`i`: Case-insensitive

Matches letters regardless of case.

/hello/i.test("HELLO"); // true
"Hello World".match(/hello/i); // ["Hello"]

`m`: Multiline

Changes ^ and $ to match the start and end of each line instead of the whole string.

const text = "hello\nworld";
/^world$/m.test(text); // true

`s`: Dotall

Makes . match newline characters too.

const html = "<div>\n  hello\n</div>";
/<div>.*<\/div>/s.test(html); // true

`u`: Unicode

Enables full Unicode matching and lets you use \u{} escapes and Unicode property escapes.

/\u{1F600}/u.test("😀"); // true
/\p{Emoji}/u.test("😀"); // true

`y`: Sticky

Matches only from the lastIndex position and does not search further.

const re = /\d+/y;
re.lastIndex = 2;
"ab12cd".match(re); // ["12"]
 
re.lastIndex = 0;
"ab12cd".match(re); // null

Character classes

Pattern	Matches
`.`	Any character except newline (Any character with `s` flag).
`[a-z]`	Any character in the range.
`\d`	Any digit (`0-9`).
`\D`	Any non-digit.
`\w`	Any word character (`a-z`, `A-Z`, `0-9`, `_`).
`\W`	Any non-word character.
`\s`	Any whitespace character.
`\S`	Any non-whitespace character.
`[abc]`	Any character in the set.
`[^abc]`	Any character not in the set.

`.`: Any character

"a".match(/./); // ["a"]
"abc".match(/./g); // ["a", "b", "c"]

`[a-z]`: Character range

"Hello".match(/[a-z]/); // ["e"]
"HELLO".match(/[a-z]/); // null

`\d`: Digit

"abc123".match(/\d+/); // ["123"]
"Room 42".match(/\d+/); // ["42"]

`\D`: Non-digit

"abc123".match(/\D+/); // ["abc"]
"2024!".match(/\D/); // ["!"]

`\w`: Word character

"hello_world".match(/\w+/); // ["hello_world"]
"user_123".match(/\w+/); // ["user_123"]

`\W`: Non-word character

"hello world".match(/\W/); // [" "]
"a@b".match(/\W/); // ["@"]

`\s`: Whitespace

"a b".match(/\s/); // [" "]
"a\tb".match(/\s/); // ["\t"]

`\S`: Non-whitespace

" a".match(/\S/); // ["a"]
"  hi".match(/\S+/); // ["hi"]

`[abc]`: Character set

"cat".match(/[aeiou]/); // ["a"]
"sky".match(/[aeiou]/); // null

`[^abc]`: Negated character set

"cat".match(/[^aeiou]/); // ["c"]
"aei".match(/[^aeiou]/); // null

Quantifiers

Pattern	Meaning
`*`	Zero or more.
`+`	One or more.
`?`	Zero or one.
`{n}`	Exactly `n` times.
`{n,}`	At least `n` times.
`{n,m}`	Between `n` and `m` times.

`*`: Zero or more

"aaab".match(/a*/); // ["aaa"]
"b".match(/a*/); // [""]

`+`: One or more

"aaab".match(/a+/); // ["aaa"]
"b".match(/a+/); // null

`?`: Zero or one

"color".match(/colou?r/); // ["color"]
"colour".match(/colou?r/); // ["colour"]

`{n}`: Exactly n times

"123".match(/\d{3}/); // ["123"]
"12".match(/\d{3}/); // null

`{n,}`: At least n times

"12345".match(/\d{3,}/); // ["12345"]
"12".match(/\d{3,}/); // null

`{n,m}`: Between n and m times

"1234".match(/\d{2,4}/); // ["1234"]
"1".match(/\d{2,4}/); // null

Anchors

Pattern	Matches
`^`	Start of string (or line in `m` mode).
`$`	End of string (or line in `m` mode).
`\b`	Word boundary.
`\B`	Non-word boundary.

`^`: Start of string

/^hello/.test("hello world"); // true
/^world/.test("hello world"); // false

`$`: End of string

/world$/.test("hello world"); // true
/hello$/.test("hello world"); // false

`\b`: Word boundary

/\bworld\b/.test("hello world"); // true
/\bworld\b/.test("helloworld"); // false

`\B`: Non-word boundary

/\Bworld\B/.test("helloworld"); // true
/\Bworld\B/.test("hello world"); // false

Groups

Pattern	Description
`(...)`	Capturing group. Stores the matched text for later use.
`(?:...)`	Non-capturing group. Groups without storing.
`(?<name>...)`	Named capturing group. Stores the match under a name.

Capturing group

const match = "2024-07-12".match(/(\d{4})-(\d{2})-(\d{2})/);
match[0]; // "2024-07-12"
match[1]; // "2024"
match[2]; // "07"
match[3]; // "12"

Non-capturing group

const match = "foo".match(/(?:foo|bar)/); // ["foo"]
match[0]; // "foo"

Named capturing group

const match = "2024-07-12".match(
  /(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})/,
);
match.groups.year; // "2024"

Lookarounds

Pattern	Description
`(?=...)`	Positive lookahead.
`(?!...)`	Negative lookahead.
`(?<=...)`	Positive lookbehind.
`(?<!...)`	Negative lookbehind.

`(?=...)`: Positive lookahead

Matches a group only if followed by another pattern.

/\d+(?=px)/.exec("100px"); // ["100"]
/\d+(?=px)/.exec("100em"); // null

`(?!...)`: Negative lookahead

Matches a group only if not followed by another pattern.

/\d+(?!px)/.exec("100em"); // ["100"]
/\d+(?!px)/.exec("100px"); // null

`(?<=...)`: Positive lookbehind

Matches a group only if preceded by another pattern.

/(?<=\$)\d+/.exec("Price: $42"); // ["42"]
/(?<=\$)\d+/.exec("Price: 42"); // null

`(?<!...)`: Negative lookbehind

Matches a group only if not preceded by another pattern.

/(?<!\$)\d+/.exec("Price: 42"); // ["42"]
/(?<!\$)\d+/.exec("Price: $42"); // null

JavaScript regex methods

`.test()`

Returns true if the pattern matches.

/hello/.test("hello world"); // true

`.match()`

Returns an array of matches.

"abc123".match(/\d+/); // ["123"]
"a1b2c3".match(/\d/g); // ["1", "2", "3"]

`.matchAll()`

Returns an iterator of all matches with capture groups.

const matches = "a1b2".matchAll(/[a-z](\d)/g);
for (const match of matches) {
  console.log(match[0], match[1]);
}

`.replace()`

Replaces the first match, or all matches with the g flag.

"hello world".replace(/world/, "JS"); // "hello JS"
"a b c".replace(/\s/g, "-"); // "a-b-c"

`.replaceAll()`

Replaces all matches without needing the g flag.

"a b c".replaceAll(" ", "-"); // "a-b-c"

`.search()`

Returns the index of the first match, or -1.

"hello world".search(/world/); // 6

`.split()`

Splits a string using a regex.

"a,b;c".split(/[,;]/); // ["a", "b", "c"]

Regular Expression Cheatsheet

Creating regex

Literal syntax

RegExp constructor

Flags

g: Global

i: Case-insensitive

m: Multiline

s: Dotall

u: Unicode

y: Sticky

Character classes

.: Any character

[a-z]: Character range

\d: Digit

\D: Non-digit

\w: Word character

\W: Non-word character

\s: Whitespace

\S: Non-whitespace

[abc]: Character set

[^abc]: Negated character set

Quantifiers

*: Zero or more

+: One or more

?: Zero or one

{n}: Exactly n times

{n,}: At least n times

{n,m}: Between n and m times

Anchors

^: Start of string

$: End of string

\b: Word boundary

\B: Non-word boundary

Groups

Capturing group

Non-capturing group

Named capturing group

Lookarounds

(?=...): Positive lookahead

(?!...): Negative lookahead

(?<=...): Positive lookbehind

(?<!...): Negative lookbehind

JavaScript regex methods

.test()

.match()

.matchAll()

.replace()

.replaceAll()

.search()

.split()

Full-Stack AI Developer Roadmap

Regular Expression Cheatsheet

Creating regex

Literal syntax

RegExp constructor

Flags

g: Global

i: Case-insensitive

m: Multiline

s: Dotall

u: Unicode

y: Sticky

Character classes

.: Any character

[a-z]: Character range

\d: Digit

\D: Non-digit

\w: Word character

\W: Non-word character

\s: Whitespace

\S: Non-whitespace

[abc]: Character set

[^abc]: Negated character set

Quantifiers

*: Zero or more

+: One or more

?: Zero or one

{n}: Exactly n times

{n,}: At least n times

`g`: Global

`i`: Case-insensitive

`m`: Multiline

`s`: Dotall

`u`: Unicode

`y`: Sticky

`.`: Any character

`[a-z]`: Character range

`\d`: Digit

`\D`: Non-digit

`\w`: Word character

`\W`: Non-word character

`\s`: Whitespace

`\S`: Non-whitespace

`[abc]`: Character set

`[^abc]`: Negated character set

`*`: Zero or more

`+`: One or more

`?`: Zero or one

`{n}`: Exactly n times

`{n,}`: At least n times

`{n,m}`: Between n and m times

`^`: Start of string

`$`: End of string

`\b`: Word boundary

`\B`: Non-word boundary

`(?=...)`: Positive lookahead

`(?!...)`: Negative lookahead

`(?<=...)`: Positive lookbehind

`(?<!...)`: Negative lookbehind

`.test()`

`.match()`

`.matchAll()`

`.replace()`

`.replaceAll()`

`.search()`

`.split()`

`g`: Global

`i`: Case-insensitive

`m`: Multiline

`s`: Dotall

`u`: Unicode

`y`: Sticky

`.`: Any character

`[a-z]`: Character range

`\d`: Digit

`\D`: Non-digit

`\w`: Word character

`\W`: Non-word character

`\s`: Whitespace

`\S`: Non-whitespace

`[abc]`: Character set

`[^abc]`: Negated character set

`*`: Zero or more

`+`: One or more

`?`: Zero or one

`{n}`: Exactly n times

`{n,}`: At least n times

`{n,m}`: Between n and m times

`^`: Start of string

`$`: End of string

`\b`: Word boundary

`\B`: Non-word boundary

`(?=...)`: Positive lookahead

`(?!...)`: Negative lookahead

`(?<=...)`: Positive lookbehind

`(?<!...)`: Negative lookbehind

`.test()`

`.match()`

`.matchAll()`

`.replace()`

`.replaceAll()`

`.search()`

`.split()`