eslint/docs/src/rules/no-misleading-character-class.md

   1 ---
   2 title: no-misleading-character-class
   3 layout: doc
   4 rule_type: problem
   5 ---
   6
   7
   8
   9
  10
  11 Unicode includes the characters which are made with multiple code points.
  12 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 `❇️`.
  13
  14 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.
  15
  16 **A character with combining characters:**
  17
  18 The combining characters are characters which belong to one of `Mc`, `Me`, and `Mn` [Unicode general categories](http://www.unicode.org/L2/L1999/UnicodeData.html#General%20Category).
  19
  20 ```js
  21 /^[Á]$/u.test("Á") //→ false
  22 /^[❇️]$/u.test("❇️") //→ false
  23 ```
  24
  25 **A character with Emoji modifiers:**
  26
  27 ```js
  28 /^[👶🏻]$/u.test("👶🏻") //→ false
  29 /^[👶🏽]$/u.test("👶🏽") //→ false
  30 ```
  31
  32 **A pair of regional indicator symbols:**
  33
  34 ```js
  35 /^[🇯🇵]$/u.test("🇯🇵") //→ false
  36 ```
  37
  38 **Characters that ZWJ joins:**
  39
  40 ```js
  41 /^[👨‍👩‍👦]$/u.test("👨‍👩‍👦") //→ false
  42 ```
  43
  44 **A surrogate pair without Unicode flag:**
  45
  46 ```js
  47 /^[👍]$/.test("👍") //→ false
  48
  49 // Surrogate pair is OK if with u flag.
  50 /^[👍]$/u.test("👍") //→ true
  51 ```
  52
  53 ## Rule Details
  54
  55 This rule reports the regular expressions which include multiple code point characters in character class syntax.
  56
  57 Examples of **incorrect** code for this rule:
  58
  59 ::: incorrect
  60
  61 ```js
  62 /*eslint no-misleading-character-class: error */
  63
  64 /^[Á]$/u
  65 /^[❇️]$/u
  66 /^[👶🏻]$/u
  67 /^[🇯🇵]$/u
  68 /^[👨‍👩‍👦]$/u
  69 /^[👍]$/
  70 ```
  71
  72 :::
  73
  74 Examples of **correct** code for this rule:
  75
  76 ::: correct
  77
  78 ```js
  79 /*eslint no-misleading-character-class: error */
  80
  81 /^[abc]$/
  82 /^[👍]$/u
  83 ```
  84
  85 :::
  86
  87 ## When Not To Use It
  88
  89 You can turn this rule off if you don't want to check RegExp character class syntax for multiple code point characters.