eslint/docs/src/rules/id-denylist.md

   1 ---
   2 title: id-denylist
   3 layout: doc
   4 rule_type: suggestion
   5 ---
   6
   7
   8 > "There are only two hard things in Computer Science: cache invalidation and naming things." — Phil Karlton
   9
  10 Generic names can lead to hard-to-decipher code. This rule allows you to specify a deny list of disallowed identifier names to avoid this practice.
  11
  12 ## Rule Details
  13
  14 This rule disallows specified identifiers in assignments and `function` definitions.
  15
  16 This rule will catch disallowed identifiers that are:
  17
  18 * variable declarations
  19 * function declarations
  20 * object properties assigned to during object creation
  21 * class fields
  22 * class methods
  23
  24 It will not catch disallowed identifiers that are:
  25
  26 * function calls (so you can still use functions you do not have control over)
  27 * object properties (so you can still use objects you do not have control over)
  28
  29 ## Options
  30
  31 The rule takes one or more strings as options: the names of restricted identifiers.
  32
  33 For example, to restrict the use of common generic identifiers:
  34
  35 ```json
  36 {
  37     "id-denylist": ["error", "data", "err", "e", "cb", "callback"]
  38 }
  39 ```
  40
  41 **Note:** The first element of the array is for the rule severity (see [configuring rules](/docs/latest/user-guide/configuring/rules). The other elements in the array are the identifiers that you want to disallow.
  42
  43 Examples of **incorrect** code for this rule with sample `"data", "callback"` restricted identifiers:
  44
  45 ::: incorrect
  46
  47 ```js
  48 /*eslint id-denylist: ["error", "data", "callback"] */
  49
  50 var data = {...};
  51
  52 function callback() {
  53     // ...
  54 }
  55
  56 element.callback = function() {
  57     // ...
  58 };
  59
  60 var itemSet = {
  61     data: [...]
  62 };
  63
  64 class Foo {
  65     data = [];
  66 }
  67
  68 class Foo {
  69     #data = [];
  70 }
  71
  72 class Foo {
  73     callback( {);
  74 }
  75
  76 class Foo {
  77     #callback( {);
  78 }
  79 ```
  80
  81 :::
  82
  83 Examples of **correct** code for this rule with sample `"data", "callback"` restricted identifiers:
  84
  85 ::: correct
  86
  87 ```js
  88 /*eslint id-denylist: ["error", "data", "callback"] */
  89
  90 var encodingOptions = {...};
  91
  92 function processFileResult() {
  93     // ...
  94 }
  95
  96 element.successHandler = function() {
  97     // ...
  98 };
  99
 100 var itemSet = {
 101     entities: [...]
 102 };
 103
 104 callback(); // all function calls are ignored
 105
 106 foo.callback(); // all function calls are ignored
 107
 108 foo.data; // all property names that are not assignments are ignored
 109
 110 class Foo {
 111     items = [];
 112 }
 113
 114 class Foo {
 115     #items = [];
 116 }
 117
 118 class Foo {
 119     method( {);
 120 }
 121
 122 class Foo {
 123     #method( {);
 124 }
 125 ```
 126
 127 :::
 128
 129 ## When Not To Use It
 130
 131 You can turn this rule off if you do not want to restrict the use of certain identifiers.