StdLib RegExp

RegExp

The RegExp built-in provides regular expression support.

Implementation Status: 100% Complete

Overview

Category	Items	Implemented
Constructor	1	1
Static Methods	1	1
Instance Methods	4	4
Symbol Methods	5	5
Property Getters	10	10
Legacy Static Props	12	12
Total	33	33

Constructor

new RegExp(pattern, flags)
new RegExp(regexp)           // Clone with optional new flags
/pattern/flags               // Literal syntax

Static Methods

Method	Status	Description
RegExp[Symbol.species]	Implemented	Returns constructor

Instance Methods

Method	Status	Description
test(string)	Implemented	Tests for match, returns boolean
exec(string)	Implemented	Executes search, returns match array
toString()	Implemented	Returns /pattern/flags string
compile(pattern, flags)	Implemented	Legacy: recompiles regexp

Symbol Methods

Method	Status	Description
[Symbol.match](string)	Implemented	Called by String.match()
[Symbol.matchAll](string)	Implemented	Called by String.matchAll()
[Symbol.replace](string, repl)	Implemented	Called by String.replace()
[Symbol.search](string)	Implemented	Called by String.search()
[Symbol.split](string, limit)	Implemented	Called by String.split()

Property Getters

Property	Status	Description
flags	Implemented	All active flags (alphabetical)
source	Implemented	Pattern string
global	Implemented	g flag
ignoreCase	Implemented	i flag
multiline	Implemented	m flag
dotAll	Implemented	s flag
unicode	Implemented	u flag
unicodeSets	Implemented	v flag (ES2024)
sticky	Implemented	y flag
hasIndices	Implemented	d flag (ES2022)

Supported Flags

Flag	Name	Description
g	global	Find all matches
i	ignoreCase	Case-insensitive
m	multiline	^ and $ match line boundaries
s	dotAll	. matches newlines
u	unicode	Unicode mode
v	unicodeSets	Unicode sets mode (ES2024)
y	sticky	Match at lastIndex only
d	hasIndices	Include indices in results

Match Result Properties

exec() and match() return arrays with extra properties:

Property	Description
[0]	Full match
[1..n]	Capture groups
index	Match position
input	Original string
groups	Named capture groups object
indices	Match indices (with d flag)

Legacy Static Properties

Property	Alias	Description
RegExp.input	$_	Last input string
RegExp.lastMatch	$&	Last matched substring
RegExp.lastParen	$+	Last parenthesized match
RegExp.leftContext	$`	Text before match
RegExp.rightContext	$'	Text after match
RegExp.$1 - $9	-	Capture group values

Implementation Notes

Pattern Translation

JavaScript patterns are translated to .NET regex with:

• Unicode support for \u{...} escapes
• Surrogate pair handling
• Named group syntax conversion

Unicode Mode (u flag)

• Full code point matching
• Surrogate pairs handled correctly
• Unicode property escapes (\p{...})

Unicode Sets Mode (v flag)

• Set notation in character classes
• String literals in character classes
• Improved Unicode support

lastIndex Behavior

• Updated after exec() with g or y flag
• Reset to 0 when match fails
• Can be set manually

Files

File	Purpose
StdLib/RegExp/RegExpConstructor.cs	Constructor
StdLib/RegExp/RegExpPrototype.cs	Methods and properties
StdLib/RegExp/RegExpHelper.cs	Internal helpers
JsTypes/JsRegExp.cs	Core implementation

See Also

• RegExp-Implementation - Deep dive into implementation
• StdLib-String - String pattern methods