RegExp.prototype.unicodeSets
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The unicodeSets accessor property of {{jsxref("RegExp")}} instances returns whether or not the v flag is used with this regular expression.
{{InteractiveExample("JavaScript Demo: RegExp.prototype.unicodeSets")}}
```js interactive-example const regex1 = /[\p{Lowercase}&&\p{Script=Greek}]/; const regex2 = /[\p{Lowercase}&&\p{Script=Greek}]/v;
console.log(regex1.unicodeSets); // Expected output: false
console.log(regex2.unicodeSets); // Expected output: true
## Description
`RegExp.prototype.unicodeSets` has the value `true` if the `v` flag was used; otherwise, `false`. The `v` flag is an "upgrade" to the [`u`](/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/unicode) flag that enables more Unicode-related features. ("v" is the next letter after "u" in the alphabet.) Because `u` and `v` interpret the same regex in incompatible ways, using both flags results in a {{jsxref("SyntaxError")}}. With the `v` flag, you get all features mentioned in the `u` flag description, plus:
- The [`\p`](/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Unicode_character_class_escape) escape sequence can be additionally used to match properties of strings, instead of just characters.
- The [character class](/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Character_class) syntax is upgraded to allow intersection, union, and subtraction syntaxes, as well as matching multiple Unicode characters.
- The character class complement syntax `[^...]` constructs a complement class instead of negating the match result, avoiding some confusing behaviors with case-insensitive matching. For more information, see [Complement classes and case-insensitive matching](/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Character_class#complement_classes_and_case-insensitive_matching).
Some valid `u`-mode regexes become invalid in `v`-mode. Specifically, the character class syntax is different and some characters can no longer appear literally. For more information, see [`v`-mode character class](/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Character_class#v-mode_character_class).
> [!NOTE]
> The `v` mode does not interpret grapheme clusters as single characters; they are still multiple code points. For example, `/[🇺🇳]/v` is still able to match `"🇺"`.
The set accessor of `unicodeSets` is `undefined`. You cannot change this property directly.
## Examples
### Using the unicodeSets property
```js
const regex = /[\p{Script_Extensions=Greek}&&\p{Letter}]/v;
console.log(regex.unicodeSets); // true
Specifications#
{{Specifications}}
Browser compatibility#
{{Compat}}
See also#
- {{jsxref("RegExp.prototype.lastIndex")}}
- {{jsxref("RegExp.prototype.dotAll")}}
- {{jsxref("RegExp.prototype.global")}}
- {{jsxref("RegExp.prototype.hasIndices")}}
- {{jsxref("RegExp.prototype.ignoreCase")}}
- {{jsxref("RegExp.prototype.multiline")}}
- {{jsxref("RegExp.prototype.source")}}
- {{jsxref("RegExp.prototype.sticky")}}
- {{jsxref("RegExp.prototype.unicode")}}
- RegExp v flag with set notation and properties of strings on v8.dev (2022)