Engine: ECMAScript

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ECMAScript

Features

The following features are supported:

✔ Flags
✔ Anchors
✔ Word Boundaries
✔ Alternatives
✔ Wildcard
✔ Character Classes
✔ Character Class Escapes
✔ Character Property Escapes
✔ Quantifiers
✔ Lazy Quantifiers
✔ Capturing Groups
✔ Named Capturing Groups
✔ Non-Capturing Groups
✔ Backreferences
✔ Lookahead
✔ Lookbehind

The following features are not supported:

❌ Buffer Boundaries
❌ Text Segment Boundaries
❌ Continuation Escape
❌ Posix Character Classes
❌ Negated Posix Character Classes
❌ Collating Elements
❌ Equivalence Classes
❌ Line Endings Escape
❌ Character Class Nested Set
❌ Character Class Intersection
❌ Character Class Union
❌ Character Class Subtraction
❌ Character Class Symmetric Difference
❌ Character Class Complement
❌ Quoted Characters
❌ Possessive Quantifiers
❌ Comments
❌ Line Comments
❌ Modifiers
❌ Branch Reset
❌ Non-Backtracking Expressions
❌ Recursion
❌ Conditional Expressions
❌ Subroutines
❌ Callouts
❌ Backtracking Control Verbs

Feature: Flags

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Flags control certain aspects of the matching behavior of a pattern.

Syntax

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The following flags are supported:

i — Ignore Case. Matches character classes using a case-insensitive comparison.
m — Multiline. Causes the anchors ^ and $ to match the start and end of each line (respectively), rather than the start and end of the input.
s — Singleline. Causes the wildcard . to match newline characters.
u — Unicode. Enforces stricter parsing of RegExp patterns, improved handling of escaped Unicode surrogate pairs, and allows the use of \u{CodePoint}.
g — Global. Indicates the match must start at or after the index specified by the lastIndex property of the RegExp. When matching completes successfully, lastIndex will be updated with the ending index of the last match.
y — Sticky. Indicates the match must start at the index specified by the lastIndex property of the RegExp. When matching completes successfully, lastIndex will be updated with the ending index of the last match.
d — Indices. Indicates the match result object will include an indices property with the start and end indices of each captured subexpression.

NOTE: This feature is at Stage 4 of the ECMA-262 specification process. See the RegExp Match Indices proposal for more information.

Feature: Anchors

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Anchors match the start or end of a line.

Syntax

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^ — Matches the start of a line when the m (multiline) flag is set. Otherwise, matches the start of the input.
$ — Matches the end of a line when the m (multiline) flag is set. Otherwise, matches the end of the input.

Feature: Buffer Boundaries

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Feature: Word Boundaries

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A Word Boundary is an Atom that matches the start or the end of a word.

Syntax

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\b — Matches the start or the end of a word.
\B — Matches when not at the start or the end of a word.

Feature: Text Segment Boundaries

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Feature: Continuation Escape

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Feature: Alternatives

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An Alternative represents two or more branches in a pattern. If first branch of a pattern fails to match, each alternative is attempted from left to right until a match is found.

Syntax

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…|… — Matches the pattern to the left of the |. If that fails, matches the pattern to the right of |.

Feature: Wildcard

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A Wildcard matches a single, non-newline character.

Syntax

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. — Matches any character except newline characters. If the s (single-line) flag is set then this matches any character.

Feature: Character Classes

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A Character Class is an Atom that specifies a set of characters to match a single character in the set.

Syntax

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[…] — Where … is one or more single characters or character class escapes, excluding ^ at the start and - between two entries in the set. Matches a character in the set. Example: [abc] matches a, b, or c.
[^…] — Where … is one or more single characters or character class escapes, excluding - between two entries in the set. Matches any character not in the set. Example: [^abc] matches d, e, or f, etc., but not a, b, or c.
[a-z] — Where a and z are single characters or character escapes. Matches any character in the range between a and z (inclusive). Example: [a-c] matches a, b, or c, but not d.

Feature: Posix Character Classes

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Feature: Negated Posix Character Classes

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Feature: Collating Elements

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Feature: Equivalence Classes

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Feature: Character Class Escapes

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A Character Class Escape is a single character escape that represents an entire character class. They can be used as an element of a Character Class or as an Atom. It is often the case that a lower-case escape character is the inclusive set, while an upper-case variant of the same character excludes that set.

Syntax

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\d — A decimal digit character in the range 0-9. Equivalent to [0-9].
\D — Any character not in the range 0-9. Equivalent to [^0-9].
\w — Any “word” character. Equivalent to [a-zA-Z0-9_].
\W — Any non-“word” character. Equivalent to [^a-zA-Z0-9_].
\s — Any whitespace character.
\S — Any non-whitespace character.

Feature: Line Endings Escape

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Feature: Character Property Escapes

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A Character Property Escape is an escape sequence used to match a character with a specific character property.

Syntax

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\pX — Where X is a single character. Matches a character that has the property X.
\p{name} — Where name is a predefined property name. Matches a character that has the property name.
\PX — Where X is a single character. Matches a character that does not have the property X.
\P{name} — Where name is a predefined property name. Matches a character that does not have the property name.

Feature: Character Class Nested Set

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Feature: Character Class Intersection

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Feature: Character Class Union

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Feature: Character Class Subtraction

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Feature: Character Class Symmetric Difference

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Feature: Character Class Complement

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Feature: Quoted Characters

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Feature: Quantifiers

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Quantifiers specify repetition of an Atom. By default, quantifiers are “greedy” in that they attempt to match as many instances of the preceding Atom as possible to satisfy the pattern before backtracking.

Syntax

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* — Matches the preceding Atom zero or more times. Example: a*b matches b, ab, aab, aaab, etc.
+ — Matches the preceding Atom one or more times. Example: a+b matches ab, aab, aaab, etc., but not b.
? — Matches the preceding Atom zero or one times. Example: a?b matches b, ab.
{n} — Where n is an integer. Matches the preceding Atom exactly n times. Example: a{2} matches aa but not a or aaa.
{n,} — Where n is an integer. Matches the preceding Atom at-least n times. Example: a{2,} matches aa, aaa, aaaa, etc., but not a.
{n,m} — Where n and m are integers, and m >= n. Matches the preceding Atom at-least n times and at-most m times. Example: a{2,3} matches aa, aaa, aaaa, etc., but not a or aaaa.

Feature: Lazy Quantifiers

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Lazy Quantifiers specify repetition of an Atom, but attempt to match as few instances of the preceding Atom as possible to satisfy the pattern before advancing.

Syntax

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*? — Matches the preceding Atom zero or more times.
+? — Matches the preceding Atom one or more times.
?? — Matches the preceding Atom zero or one times.
{n}? — Where n is an integer. Matches the preceding Atom exactly n times.
{n,}? — Where n is an integer. Matches the preceding Atom at-least n times.
{n,m}? — Where n and m are integers, and m >= n. Matches the preceding Atom at-least n times and at-most m times.

Feature: Possessive Quantifiers

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Feature: Capturing Groups

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A Capturing Group is a subexpression that can be treated as an Atom and can be repeated using Quantifiers and referenced using Backreferences by index. A Capturing Group can be captured and returned by the matching algorithm.

Syntax

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(…) — Groups the subexpression as a single Atom. The result is captured and returned by the matching algorithm.

Feature: Named Capturing Groups

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A Named Capturing Group is a subexpression that can be captured and returned by the matching algorithm. A Named Capturing Group is also an Atom and can be repeated using Quantifiers and referenced using Backreferences by name.

Syntax

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(?<name>…) — Groups the subexpression as a single Atom associated with the provided name. The result is captured and returned by the matching algorithm.

Feature: Non-Capturing Groups

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A Non-capturing Group is a subexpression that can be treated as an Atom and can be repeated using Quantifiers but cannot be referenced using Backreferences. A Non-capturing Group is not captured by the matching algorithm.

Syntax

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(?:…) — Groups the subexpression as a single Atom.

Feature: Backreferences

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Backreferences allow a pattern to re-match a previously matched capture group^{1 2} either by number (n) or by name.

Syntax

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\n — Where n is a decimal digit in the range 1-9. Matches the same string as the capture group n.
\k<name> — Matches the same string as the named capture group with the name name.

Feature: Comments

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Feature: Line Comments

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Feature: Modifiers

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Feature: Branch Reset

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Feature: Lookahead

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A Lookahead is a zero-width assertion that matches if the provided pattern would match the characters to the right of the current position.

Syntax

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(?=…) — Positive Lookahead. Matches if the provided pattern would match but does not advance the current position.
(?!…) — Negative Lookahead. Matches if the provided pattern would not match, but does not advance the current position.

Feature: Lookbehind

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A Lookbehind is a zero-width assertion that matches if the provided pattern would match the characters to the left of the current position.

Syntax

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(?<=…) — Positive Lookbehind. Matches if the provided pattern would match the preceding characters, but does not advance the current position. The pattern must have a fixed length (unbounded quantifiers are not permitted).
(?<!…) — Negative Lookbehind. Matches if the provided pattern would not match the preceding characters, but does not advance the current position. The pattern must have a fixed length (unbounded quantifiers are not permitted).

Feature: Non-Backtracking Expressions

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Feature: Recursion

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Feature: Conditional Expressions

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Feature: Subroutines

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Feature: Callouts

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Feature: Backtracking Control Verbs

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Engine: ECMAScript

Languages

Features

Feature: Flags

Syntax

See Also

Feature: Anchors

Syntax

See Also

Feature: Buffer Boundaries

See Also

Feature: Word Boundaries

Syntax

See Also

Feature: Text Segment Boundaries

See Also

Feature: Continuation Escape

See Also

Feature: Alternatives

Syntax

Feature: Wildcard

Syntax

Feature: Character Classes

Syntax

See Also

Feature: Posix Character Classes

See Also

Feature: Negated Posix Character Classes

See Also

Feature: Collating Elements

See Also

Feature: Equivalence Classes

See Also

Feature: Character Class Escapes

Syntax

See Also

Feature: Line Endings Escape

See Also

Feature: Character Property Escapes

Syntax

See Also

Feature: Character Class Nested Set

See Also

Feature: Character Class Intersection

See Also

Feature: Character Class Union

See Also

Feature: Character Class Subtraction

See Also

Feature: Character Class Symmetric Difference

See Also

Feature: Character Class Complement

See Also

Feature: Quoted Characters

Feature: Quantifiers

Syntax

See Also

Feature: Lazy Quantifiers

Syntax

See Also

Feature: Possessive Quantifiers

See Also

Feature: Capturing Groups

Syntax

See Also

Feature: Named Capturing Groups

Syntax

See Also

Feature: Non-Capturing Groups

Syntax

See Also

Feature: Backreferences

Syntax

See Also

Feature: Comments

See Also

Feature: Line Comments

See Also

Feature: Modifiers

See Also