Flash cards
Review the key moves
What is the main idea behind JavaScript RegExp Flags?
Lesson checks
Practice each idea before moving on
Short Mimo-style checks built from this lesson's code, terms, and sequence.
Which statement best captures the main point of this lesson?
Put the learning moves in the order that makes the concept easiest to apply.
RegExp Modifier Flags
Flags are parameters that can modify how a regex pattern is used, such as making it case-insensitive or global.
/pattern/
flagsJavaScript Regex Flags
| Flag | Description |
|---|---|
| /d | Performs substring matches (new 2022) |
| /g | Performs a global match (find all) |
| /i | Performs case-insensitive matching |
| /m | Performs multiline matching |
| /s | Allows . (dot) to match line terminators (new 2018) |
| /u | Enables Unicode support (new 2015) |
| /v | An upgrade to the /u flag for better Unicode support (new 2025) |
| /y | Performs a "sticky" search (new 2015) |
Flag Syntax: /pattern/flags
| / | Opening delimiter for the regular expression |
|---|---|
| pattern | Regular expression (a search criteria) |
| / | Closing delimiter for the regular expression |
| flags | One or more single modifier 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 ExampleSite";
const pattern = /is/g;
let result = text.match(pattern);RegExp /d Flag
The /d flag specifies the start and the end of a match.
Example
let text = "aaaabb";
const pattern = /(aa)(bb)/d;
let result = text.match(pattern);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 /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);The example above uses a regex metacharacter /\w+/.
The meaning of /\w+/ is "mach any word".
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);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 = "ExampleSite tutorials.";
const pattern = /(?i:WShools) tutorials/;
// Returns true: let result = pattern.test(text);JavaScript Regex Flag Properties
| Property | Description |
|---|---|
| global | Returns true if the /g flag is set |
| hasIndices | Returns true if the /d flag is set |
| ignoreCase | Returns true if the /i flag is set |
| multiline | Returns true if the /m flag is set |
| dotAll | Returns true if the /s flag is set |
| sticky | Returns true if the /y flag is set |
| unicode | Returns true if the /u flag is set |
| unicodeSets | Returns true if the /v flag is set |
The dotAll Property
The dotAll property returns true if the /s flag is set.
Example
const pattern = /ExampleSite/s;
let result = pattern.dotAll;The global Property
The global property returns true if the /g flag is set.
Example
const pattern = /ExampleSite/g;
let result = pattern.global;The hasIndices Property
The hasIndices property returns true if the /d flag is set.
Example
const pattern = /ExampleSite/d;
let result = pattern.hasIndices;The ignoreCase Property
The ignoreCase property returns true if the /i flag is set.
Example
const pattern = /ExampleSite/i;
let result = pattern.ignoreCase;The multiline Property
The multiline property returns true if the /m flag is set.
Example
const pattern = /ExampleSite/m;
let result = pattern.multiline;The sticky Property
The sticky property returns true if the /y flag is set.
Example
const pattern = /ExampleSite/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.
String Methods
| Method | Description |
|---|---|
| match( regex ) | Returns an Array of results |
| matchAll( regex ) | Returns an Iterator of results |
| replace( regex ) | Returns a new String |
| replaceAll( regex ) | Returns a new String |
| search( regex ) | Returns the index of the first match |
| split( regex ) | Returns an Array of results |
RegExp Methods
| Method | Description |
|---|---|
| regex .exec() | Returns an Iterator of results |
| regex .test() | Returns true or false |
See Also
JavaScript RegExp Character Classes
JavaScript RegExp Meta Characters
JavaScript RegExp Assertions
JavaScript RegExp Quantifiers
JavaScript RegExp Patterns
JavaScript RegExp Objects
JavaScript RegExp Methods