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noDuplicateCase (since v1.0.0)

Diagnostic Category: lint/suspicious/noDuplicateCase

Sources:

Disallow duplicate case labels.

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.

Examples

Section titled Examples

Invalid

Section titled Invalid
switch (a) {
    case 1:
        break;
    case 1:
        break;
    default:
        break;
}
code-block.js:4:10 lint/suspicious/noDuplicateCase ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Duplicate case label.
  
    2 │     case 1:
    3 │         break;
  > 4 │     case 1:
      │          ^
    5 │         break;
    6 │     default:
  
  ℹ The first similar label is here:
  
    1 │ switch (a) {
  > 2 │     case 1:
      │          ^
    3 │         break;
    4 │     case 1:
  

switch (a) {
    case one:
        break;
    case one:
        break;
    default:
        break;
}
code-block.js:4:10 lint/suspicious/noDuplicateCase ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Duplicate case label.
  
    2 │     case one:
    3 │         break;
  > 4 │     case one:
      │          ^^^
    5 │         break;
    6 │     default:
  
  ℹ The first similar label is here:
  
    1 │ switch (a) {
  > 2 │     case one:
      │          ^^^
    3 │         break;
    4 │     case one:
  

switch (a) {
    case "1":
        break;
    case "1":
        break;
    default:
        break;
}
code-block.js:4:10 lint/suspicious/noDuplicateCase ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Duplicate case label.
  
    2 │     case "1":
    3 │         break;
  > 4 │     case "1":
      │          ^^^
    5 │         break;
    6 │     default:
  
  ℹ The first similar label is here:
  
    1 │ switch (a) {
  > 2 │     case "1":
      │          ^^^
    3 │         break;
    4 │     case "1":

Valid

Section titled Valid
switch (a) {
    case 1:
        break;
    case 2:
        break;
    default:
        break;
}
switch (a) {
    case one:
        break;
    case two:
        break;
    default:
        break;
}
switch (a) {
    case "1":
        break;
    case "2":
        break;
    default:
        break;
}
Section titled Related links