eslint/docs/rules/no-duplicate-case.md

   1 # Rule to disallow a duplicate case label (no-duplicate-case)
   2
   3 If a `switch` statement has duplicate test expressions in `case` clauses, it is likely that a programmer copied a `case` clause but forgot to change the test expression.
   4
   5 ## Rule Details
   6
   7 This rule disallows duplicate test expressions in `case` clauses of `switch` statements.
   8
   9 Examples of **incorrect** code for this rule:
  10
  11 ```js
  12 /*eslint no-duplicate-case: "error"*/
  13
  14 var a = 1,
  15     one = 1;
  16
  17 switch (a) {
  18     case 1:
  19         break;
  20     case 2:
  21         break;
  22     case 1:         // duplicate test expression
  23         break;
  24     default:
  25         break;
  26 }
  27
  28 switch (a) {
  29     case one:
  30         break;
  31     case 2:
  32         break;
  33     case one:         // duplicate test expression
  34         break;
  35     default:
  36         break;
  37 }
  38
  39 switch (a) {
  40     case "1":
  41         break;
  42     case "2":
  43         break;
  44     case "1":         // duplicate test expression
  45         break;
  46     default:
  47         break;
  48 }
  49 ```
  50
  51 Examples of **correct** code for this rule:
  52
  53 ```js
  54 /*eslint no-duplicate-case: "error"*/
  55
  56 var a = 1,
  57     one = 1;
  58
  59 switch (a) {
  60     case 1:
  61         break;
  62     case 2:
  63         break;
  64     case 3:
  65         break;
  66     default:
  67         break;
  68 }
  69
  70 switch (a) {
  71     case one:
  72         break;
  73     case 2:
  74         break;
  75     case 3:
  76         break;
  77     default:
  78         break;
  79 }
  80
  81 switch (a) {
  82     case "1":
  83         break;
  84     case "2":
  85         break;
  86     case "3":
  87         break;
  88     default:
  89         break;
  90 }
  91 ```