eslint/docs/src/rules/default-case.md

   1 ---
   2 title: default-case
   3 layout: doc
   4 rule_type: suggestion
   5 related_rules:
   6 - no-fallthrough
   7 ---
   8
   9
  10 Some code conventions require that all `switch` statements have a `default` case, even if the default case is empty, such as:
  11
  12 ```js
  13 switch (foo) {
  14     case 1:
  15         doSomething();
  16         break;
  17
  18     case 2:
  19         doSomething();
  20         break;
  21
  22     default:
  23     // do nothing
  24 }
  25 ```
  26
  27 The thinking is that it's better to always explicitly state what the default behavior should be so that it's clear whether or not the developer forgot to include the default behavior by mistake.
  28
  29 Other code conventions allow you to skip the `default` case so long as there is a comment indicating the omission is intentional, such as:
  30
  31 ```js
  32 switch (foo) {
  33     case 1:
  34         doSomething();
  35         break;
  36
  37     case 2:
  38         doSomething();
  39         break;
  40
  41     // no default
  42 }
  43 ```
  44
  45 Once again, the intent here is to show that the developer intended for there to be no default behavior.
  46
  47 ## Rule Details
  48
  49 This rule aims to require `default` case in `switch` statements. You may optionally include a `// no default` after the last `case` if there is no `default` case. The comment may be in any desired case, such as `// No Default`.
  50
  51 Examples of **incorrect** code for this rule:
  52
  53 ::: incorrect
  54
  55 ```js
  56 /*eslint default-case: "error"*/
  57
  58 switch (a) {
  59     case 1:
  60         /* code */
  61         break;
  62 }
  63
  64 ```
  65
  66 :::
  67
  68 Examples of **correct** code for this rule:
  69
  70 ::: correct
  71
  72 ```js
  73 /*eslint default-case: "error"*/
  74
  75 switch (a) {
  76     case 1:
  77         /* code */
  78         break;
  79
  80     default:
  81         /* code */
  82         break;
  83 }
  84
  85 switch (a) {
  86     case 1:
  87         /* code */
  88         break;
  89
  90     // no default
  91 }
  92
  93 switch (a) {
  94     case 1:
  95         /* code */
  96         break;
  97
  98     // No Default
  99 }
 100 ```
 101
 102 :::
 103
 104 ## Options
 105
 106 This rule accepts a single options argument:
 107
 108 * Set the `commentPattern` option to a regular expression string to change the default `/^no default$/i` comment test pattern
 109
 110 ### commentPattern
 111
 112 Examples of **correct** code for the `{ "commentPattern": "^skip\\sdefault" }` option:
 113
 114 ::: correct
 115
 116 ```js
 117 /*eslint default-case: ["error", { "commentPattern": "^skip\\sdefault" }]*/
 118
 119 switch(a) {
 120     case 1:
 121         /* code */
 122         break;
 123
 124     // skip default
 125 }
 126
 127 switch(a) {
 128     case 1:
 129         /* code */
 130         break;
 131
 132     // skip default case
 133 }
 134 ```
 135
 136 :::
 137
 138 ## When Not To Use It
 139
 140 If you don't want to enforce a `default` case for `switch` statements, you can safely disable this rule.