JS RegExp Flags

RegExp Modifier Flags

Flags are parameters that can modify how a regex pattern is used, such as making it case-insensitive or global.

/pattern/flags

JavaScript Regex Flags

Revised July 2025

Flag Syntax: /pattern/flags

RegExp /g Flag (Global)

The /g flag matches all occurrences of the pattern, rather than just the first one.

Example

let text = "Is this all there is?";

const pattern = /is/g;

let result = text.match(pattern);

RegExp /i Flag (Insensitive)

The /i flag makes the match case-insensitive: /abc/i matches "abc", "AbC", "ABC".

Example

let text = "Visit W3Schools";

const pattern = /is/g;

let result = text.match(pattern);

RegExp /d Flag

The /d flag (the Indices flag) is used to find the start and end positions of substrings captured by regular expression groups.

It does not change the regex match. It provides metadata about the result.

The array returned by exec() or match() includes an additional indices property: An array of pairs representing the [start, end] index of a specific capture group.

Example

let text = "aaaabb";

const pattern = /(aa)(bb)/d;

let result = text.match(pattern);

let indexes = result.indices;

You can check if a regex has the /d flag using the hasIndices property.

RegExp /s Flag (Single line/DotAll)

The /s flag allows the . (dot) metacharacter to match newline characters (\n) in addition to any other character.

Example

let text = "Line\nLine.";

const pattern = /Line./gs;

let result = text.match(pattern);

RegExp /m Flag (Multiline)

The /m (multiline) flag specifies a multiline match.

Example

let text = `Is this

all there

is`

let pattern = /^is/m;

The /m flag affects the behavior of ^ and $.

^ specifies a match at the start of a string.

$ specifies a match at the end of a string.

With /m set, ^ and $ will match the start and end of each line, in a multiline string, in addition to the start and end of the entire string.

RegExp /y Flag (Sticky):

The /y flag performs a "sticky" search from the lastIndex property of the RegExp object.

The /y flag lets a match start at the exact position where the last match ended.

Examples

let text = "abc def ghi";

const pattern = /\w+/y;

// Start match from position 4

pattern.lastIndex = 4;

let result = text.match(pattern);

Note: The example above uses a regex metacharacter \w The meaning of /\w/ is "match an (alphanumeric) word character". The meaning of /\w+/ is "match one or more word characters". You will learn more about metacharacters in the next chapters.

RegExp /u Flag (Unicode)

The /u flag enables full Unicode support in a regular expression.

By default, JavaScript RegExp treats 4-byte Unicode characters (like emojis or less common symbols) as two separate 2-byte "surrogate" code units.

The /u flag treats the pattern as a sequence of Unicode code points, which is important for correctly handling of characters outside the Basic Multilingual Plane (BMP).

Example

let text = "䷀";

const pattern = /\u{04DC0}/u;

// Returns true:

let result = pattern.test(text);

Without the /u flag, regular expressions are not "Unicode-aware".

Example

let text = "䷀";

const pattern = /\u{04DC0}/;

// Returns false:

let result = pattern.test(text);

Note: JavaScript 2025 introduced the /v flag as an "upgrade" to the /u flag. The /v Flag enables more Unicode-related features.

RegExp /v Flag (Unicode Sets)

The /v flag is an upgrade to the /u flag for better Unicode support.

It enables more Unicode-related features.

The new features are:

• The \p escape sequence matches strings, instead of just characters.
• The character class is upgraded to allow intersection, union, and subtraction syntaxes, as well as matching multiple Unicode characters.

Example

let text = "Hello 😄";

const pattern = /\p{Emoji}/v;

// Returns true:

let result = pattern.test(text);

Without the /v flag, regular expressions are not "Unicode-aware".

Example

let text = "Hello 😄";

const pattern = /\p{Emoji}/;

// Returns false:

let result = pattern.test(text);

RegExp Group Modifiers (?flag)

The (?flag) syntax is a group modifier (inline flag modifier).

It allows for modifying flags in a part of a pattern, rather than to the entire pattern.

(?flags:pattern) enables the flags only for the pattern in the group.

Example

let text = "W3Schools tutorials.";

const pattern = /(?i:WShools) tutorials/;

// Returns true:

let result = pattern.test(text);

JavaScript Regex Flag Properties

Revised July 2025

The dotAll Property

The dotAll property returns true if the /s flag is set.

Example

const pattern = /W3Schools/s;

let result = pattern.dotAll;

The global Property

The global property returns true if the /g flag is set.

Example

const pattern = /W3Schools/g;

let result = pattern.global;

The hasIndices Property

The hasIndices property returns true if the /d flag is set.

Example

const pattern = /W3Schools/d;

let result = pattern.hasIndices;

The ignoreCase Property

The ignoreCase property returns true if the /i flag is set.

Example

const pattern = /W3Schools/i;

let result = pattern.ignoreCase;

The multiline Property

The multiline property returns true if the /m flag is set.

Example

const pattern = /W3Schools/m;

let result = pattern.multiline;

The sticky Property

The sticky property returns true if the /y flag is set.

Example

const pattern = /W3Schools/y;

let result = pattern.sticky;

The unicode Property

The unicode property returns true if the /u flag is set.

Example

let text = "䷀";

const pattern = /\u{04DC0}/u;

let result = pattern.unicode;

The unicodeSets Property

The unicodeSets property returns true if the /v flag is set.

Example

let text = "Hello 😄";

const pattern = /\p{Emoji}/v;

let result = pattern.unicodeSets;

Regular Expression Methods

Regular Expression Search and Replace can be done with different methods.

These are the most common:

String Methods

RegExp Methods

Note: See Also: JavaScript RegExp Tutorial JavaScript RegExp Character Classes JavaScript RegExp Meta Characters JavaScript RegExp Assertions JavaScript RegExp Groups JavaScript RegExp Quantifiers JavaScript RegExp Patterns JavaScript RegExp Objects JavaScript RegExp Methods