no-misleading-character-class.md

no-misleading-character-class

Disallows characters which are made with multiple code points in character class syntax.

Unicode includes the characters which are made with multiple code points. RegExp character class syntax (/[abc]/) cannot handle characters which are made by multiple code points as a character; those characters will be dissolved to each code point. For example, ❇️ is made by ❇ (U+2747) and VARIATION SELECTOR-16 (U+FE0F). If this character is in RegExp character class, it will match to either ❇ (U+2747) or VARIATION SELECTOR-16 (U+FE0F) rather than ❇️.

This rule reports the regular expressions which include multiple code point characters in character class syntax. This rule considers the following characters as multiple code point characters.

A character with combining characters:

The combining characters are characters which belong to one of Mc, Me, and Mn Unicode general categories.

/^[Á]$/u.test("Á") //→ false
/^[❇️]$/u.test("❇️") //→ false

A character with Emoji modifiers:

/^[👶🏻]$/u.test("👶🏻") //→ false
/^[👶🏽]$/u.test("👶🏽") //→ false

A pair of regional indicator symbols:

/^[🇯🇵]$/u.test("🇯🇵") //→ false

Characters that ZWJ joins:

/^[👨‍👩‍👦]$/u.test("👨‍👩‍👦") //→ false

A surrogate pair without Unicode flag:

/^[👍]$/.test("👍") //→ false

// Surrogate pair is OK if with u flag.
/^[👍]$/u.test("👍") //→ true

Rule Details

This rule reports the regular expressions which include multiple code point characters in character class syntax.

Examples of incorrect code for this rule:

/*eslint no-misleading-character-class: error */

/^[Á]$/u
/^[❇️]$/u
/^[👶🏻]$/u
/^[🇯🇵]$/u
/^[👨‍👩‍👦]$/u
/^[👍]$/

Examples of correct code for this rule:

/*eslint no-misleading-character-class: error */

/^[abc]$/
/^[👍]$/u

When Not To Use It

You can turn this rule off if you don't want to check RegExp character class syntax for multiple code point characters.