noDuplicateCase (JavaScript)

Language JavaScript (and super languages)

Summary

Rule available since: v1.0.0
Diagnostic Category: lint/suspicious/noDuplicateCase
This rule is recommended, meaning it is enabled by default.
This rule doesn’t have a fix.
The default severity of this rule is error.
Sources:
- Same as no-duplicate-case

How to configure

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{
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  "linter": {
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    "rules": {
4
      "suspicious": {
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        "noDuplicateCase": "error"
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      }
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    }
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  }
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}

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

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switch (a) {
2
    case 1:
3
        break;
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    case 1:
5
        break;
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    default:
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        break;
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}

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:
  
  ℹ Only the first matching case is selected. If it does not break or return, execution can fall through to this duplicate's body. It is probably a copy-paste mistake.
  
  ℹ Remove the duplicate case, or change its value to the one you meant.

1
switch (a) {
2
    case one:
3
        break;
4
    case one:
5
        break;
6
    default:
7
        break;
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}

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:
  
  ℹ Only the first matching case is selected. If it does not break or return, execution can fall through to this duplicate's body. It is probably a copy-paste mistake.
  
  ℹ Remove the duplicate case, or change its value to the one you meant.

1
switch (a) {
2
    case "1":
3
        break;
4
    case "1":
5
        break;
6
    default:
7
        break;
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}

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":
  
  ℹ Only the first matching case is selected. If it does not break or return, execution can fall through to this duplicate's body. It is probably a copy-paste mistake.
  
  ℹ Remove the duplicate case, or change its value to the one you meant.

Valid

1
switch (a) {
2
    case 1:
3
        break;
4
    case 2:
5
        break;
6
    default:
7
        break;
8
}

1
switch (a) {
2
    case one:
3
        break;
4
    case two:
5
        break;
6
    default:
7
        break;
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}

1
switch (a) {
2
    case "1":
3
        break;
4
    case "2":
5
        break;
6
    default:
7
        break;
8
}