noDuplicateCase

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Diagnostic Category: lint/suspicious/noDuplicateCase

JavaScript (and super languages)

Since: v1.0.0

Sources:

Same as: no-duplicate-case

Description

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

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

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;
}

How to configure

{
  "linter": {
    "rules": {
      "suspicious": {
        "noDuplicateCase": "error"
      }
    }
  }
}