Duplicate Property Name in Object Literal

ID

javascript.property_names_uniqueness

Severity

high

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

JavaScript

Tags

dead-code, reliability, suspicious-comparison

Description

Reports object literals whose properties contain the same name twice. The later definition silently overwrites the earlier one — JavaScript does not warn — and the bug is invisible until a downstream consumer reads the property and gets the wrong value.

Getter / setter pairs (one get x() {} and one set x(v) {}) are tracked as separate slots and are not flagged against each other. Spread elements (…​other) have no static name and are ignored.

Rationale

  • The duplicate is almost always a copy-paste leftover: someone duplicated a property to add a new one and forgot to rename the key.

  • The bug stays silent in code review because the eye reads two distinct keys but the runtime only honours one.

// Bad - second `name` wins
const config = {
  name: "primary",
  port: 8080,
  name: "secondary"
};

Remediation

Rename one of the duplicates, or remove the redundant entry.

// Good
const config = {
  primaryName: "primary",
  port: 8080,
  secondaryName: "secondary"
};

References