classMemberDuplicates

Reports duplicate class member names that will be overwritten.

✅ This rule is included in the ts untyped presets.

Duplicate class members are legal in JavaScript, but only the last definition is used. This can lead to confusion and bugs, especially when maintaining the code.

Examples

❌ Incorrect

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

class Foo {
  get bar() {
    return 1;
  }
  get bar() {
    return 2;
  }
}

class Foo {
  bar = 1;
  bar = 2;
}

✅ Correct

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

class Foo {
  get bar() {
    return 1;
  }
  set bar(value) {}
}

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

Options

This rule is not configurable.

When Not To Use It

This rule should generally always be enabled. There is no valid use case for duplicate class member names.

Further Reading

• MDN documentation on classes

Equivalents in Other Linters

• Biome: noDuplicateClassMembers
• Deno: no-dupe-class-members
• ESLint: no-dupe-class-members@typescript-eslint/no-dupe-class-members
• Oxlint: eslint/no-dupe-class-members