noDuplicateClassMembers (JavaScript)

Language JavaScript (and super languages)

Summary

Rule available since: v1.0.0
Diagnostic Category: lint/suspicious/noDuplicateClassMembers
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-dupe-class-members
- Same as @typescript-eslint/no-dupe-class-members

How to configure

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

Description

Disallow duplicate class members.

If there are declarations of the same name among class members, the last declaration overwrites other declarations silently. It can cause unexpected behaviours.

Examples

Invalid

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class Foo {
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  bar() { }
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  bar() { }
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}

code-block.js:3:3 lint/suspicious/noDuplicateClassMembers ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Duplicate class member name bar.
  
    1 │ class Foo {
    2 │   bar() { }
  > 3 │   bar() { }
      │   ^^^^^^^^^
    4 │ }
    5 │ 
  
  ℹ The last declaration silently overwrites the earlier ones, which can cause unexpected behavior.
  
  ℹ Remove the duplicate member, or rename it if you meant a different member.

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class Foo {
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  bar() { }
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  get bar() { }
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}

code-block.js:3:3 lint/suspicious/noDuplicateClassMembers ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Duplicate class member name bar.
  
    1 │ class Foo {
    2 │   bar() { }
  > 3 │   get bar() { }
      │   ^^^^^^^^^^^^^
    4 │ }
    5 │ 
  
  ℹ The last declaration silently overwrites the earlier ones, which can cause unexpected behavior.
  
  ℹ Remove the duplicate member, or rename it if you meant a different member.

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class Foo {
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  bar;
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  bar() { }
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}

code-block.js:3:3 lint/suspicious/noDuplicateClassMembers ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Duplicate class member name bar.
  
    1 │ class Foo {
    2 │   bar;
  > 3 │   bar() { }
      │   ^^^^^^^^^
    4 │ }
    5 │ 
  
  ℹ The last declaration silently overwrites the earlier ones, which can cause unexpected behavior.
  
  ℹ Remove the duplicate member, or rename it if you meant a different member.

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class Foo {
2
  static bar() { }
3
  static bar() { }
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}

code-block.js:3:3 lint/suspicious/noDuplicateClassMembers ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Duplicate class member name bar.
  
    1 │ class Foo {
    2 │   static bar() { }
  > 3 │   static bar() { }
      │   ^^^^^^^^^^^^^^^^
    4 │ }
    5 │ 
  
  ℹ The last declaration silently overwrites the earlier ones, which can cause unexpected behavior.
  
  ℹ Remove the duplicate member, or rename it if you meant a different member.

Valid

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class Foo {
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  bar() { }
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  qux() { }
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}

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class Foo {
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  set bar(value) { }
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  get bar() { }
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}

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class Foo {
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  bar;
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  qux;
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}

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class Foo {
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  bar;
3
  qux() { }
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}

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class Foo {
2
  static bar() { }
3
  bar() { }
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}