Duplicate Class Member

javascript.no_dupe_class_members

Severity

high

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

JavaScript

Description

Reports class declarations that contain two methods (or static methods, getters, or setters) with the same name in the same slot. The later definition silently shadows the earlier one — JavaScript does not warn — so calls bind to whichever happens to come last.

Rationale

The duplicate is almost always a copy-paste leftover or an unfinished refactor.
The bug is invisible until someone removes the second definition and the original behaviour reappears.
Static and instance members with the same name are not a duplicate — they live in different slots.
Getters and setters can share a name with each other (that’s how accessor pairs are written) but shadow regular methods of the same name; the rule treats them as separate slots.

// Bad - the first foo() is dead
class C {
  foo() { return 1; }
  foo() { return 2; }
}

Remediation

Rename one of the methods, or remove the duplicate.

// Good
class C {
  fooLegacy() { return 1; }
  foo() { return 2; }
}

References

MDN — Classes