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

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