loneProperty

A lone Unicode property name or value, following the same syntax as value. It specifies the value for the General_Category property, or a binary property name. In v mode, it can also be a binary Unicode property of strings.

Note: ICU syntax allows omitting the Script property name as well, but JavaScript does not support this, because most of the time Script_Extensions is more useful than Script.

property

A Unicode property name. Must be made of ASCII letters (A–Z, a–z) and underscores (_), and must be one of the non-binary property names.

value

A Unicode property value. Must be made of ASCII letters (A–Z, a–z), underscores (_), and digits (0–9), and must be one of the supported values listed in PropertyValueAliases.txt.

\p and \P are only supported in Unicode-aware mode. In Unicode-unaware mode, they are identity escapes for the p or P character.

Every Unicode character has a set of properties that describe it. For example, the character a has the General_Category property with value Lowercase_Letter, and the Script property with value Latn. The \p and \P escape sequences allow you to match a character based on its properties. For example, a can be matched by \p{Lowercase_Letter} (the General_Category property name is optional) as well as \p{Script=Latn}. \P creates a complement class that consists of code points without the specified property.

To compose multiple properties, use the character set intersection syntax enabled with the v flag, or see pattern subtraction and intersection.

In v mode, \p may match a sequence of code points, defined in Unicode as "properties of strings". This is most useful for emojis, which are often composed of multiple code points. However, \P can only complement character properties.

General categories are used to classify Unicode characters and subcategories are available to define a more precise categorization. It is possible to use both short or long forms in Unicode property escapes.

They can be used to match letters, numbers, symbols, punctuations, spaces, etc. For a more exhaustive list of general categories, please refer to the Unicode specification.

// finding all the letters of a text
const story = "It's the Cheshire Cat: now I shall have somebody to talk to.";

// Most explicit form
story.match(/\p{General_Category=Letter}/gu);

// It is not mandatory to use the property name for General categories
story.match(/\p{Letter}/gu);

// This is equivalent (short alias):
story.match(/\p{L}/gu);

// This is also equivalent (conjunction of all the subcategories using short aliases)
story.match(/\p{Lu}|\p{Ll}|\p{Lt}|\p{Lm}|\p{Lo}/gu);

Some languages use different scripts for their writing system. For instance, English and Spanish are written using the Latin script while Arabic and Russian are written with other scripts (respectively Arabic and Cyrillic). The Script and Script_Extensions Unicode properties allow regular expression to match characters according to the script they are mainly used with (Script) or according to the set of scripts they belong to (Script_Extensions).

For example, A belongs to the Latin script and ε to the Greek script.

const mixedCharacters = "aεЛ";

// Using the canonical "long" name of the script
mixedCharacters.match(/\p{Script=Latin}/u); // a

// Using a short alias (ISO 15924 code) for the script
mixedCharacters.match(/\p{Script=Grek}/u); // ε

// Using the short name sc for the Script property
mixedCharacters.match(/\p{sc=Cyrillic}/u); // Л

For more details, refer to the Unicode specification, the Scripts table in the ECMAScript specification, and the ISO 15924 list of script codes.

If a character is used in a limited set of scripts, the Script property will only match for the "predominant" used script. If we want to match characters based on a "non-predominant" script, we could use the Script_Extensions property (Scx for short).

// ٢ is the digit 2 in Arabic-Indic notation
// while it is predominantly written within the Arabic script
// it can also be written in the Thaana script

"٢".match(/\p{Script=Thaana}/u);
// null as Thaana is not the predominant script

"٢".match(/\p{Script_Extensions=Thaana}/u);
// ["٢", index: 0, input: "٢", groups: undefined]

With JavaScript regular expressions, it is also possible to use character classes and especially \w or \d to match letters or digits. However, such forms only match characters from the Latin script (in other words, a to z and A to Z for \w and 0 to 9 for \d). As shown in this example, it might be a bit clumsy to work with non Latin texts.

Unicode property escapes categories encompass much more characters and \p{Letter} or \p{Number} will work for any script.

// Trying to use ranges to avoid \w limitations:

const nonEnglishText = "Приключения Алисы в Стране чудес";
const regexpBMPWord = /([\u0000-\u0019\u0021-\uFFFF])+/gu;
// BMP goes through U+0000 to U+FFFF but space is U+0020

console.table(nonEnglishText.match(regexpBMPWord));

// Using Unicode property escapes instead
const regexpUPE = /\p{L}+/gu;
console.table(nonEnglishText.match(regexpUPE));

The following example matches prices in a string:

function getPrices(str) {
  // Sc stands for "currency symbol"
  return [...str.matchAll(/\p{Sc}\s*[\d.,]+/gu)].map((match) => match[0]);
}

const str = `California rolls $6.99
Crunchy rolls $8.49
Shrimp tempura $10.99`;
console.log(getPrices(str)); // ["$6.99", "$8.49", "$10.99"]

const str2 = `US store $19.99
Europe store €18.99
Japan store ¥2000`;
console.log(getPrices(str2)); // ["$19.99", "€18.99", "¥2000"]

With the v flag, \p{…} can match strings that are potentially longer than one character by using a property of strings:

const flag = "🇺🇳";
console.log(flag.length); // 2
console.log(/\p{RGI_Emoji_Flag_Sequence}/v.exec(flag)); // [ '🇺🇳' ]

However, you can't use \P to match "a string that does not have a property", because it's unclear how many characters should be consumed.

/\P{RGI_Emoji_Flag_Sequence}/v; // SyntaxError: Invalid regular expression: Invalid property name

• Character classes guide
• Regular expressions
• Character class: [...], [^...]
• Character class escape: \d, \D, \w, \W, \s, \S
• Character escape: \n, \u{...}
• Disjunction: |
• Unicode character property on Wikipedia
• ES2018: RegExp Unicode property escapes by Dr. Axel Rauschmayer (2017)
• Unicode regular expressions § Properties
• Unicode Utilities: UnicodeSet
• RegExp v flag with set notation and properties of strings on v8.dev (2022)