Ternary With Identical Branches

ID

javascript.ternary_identical_branches

Severity

low

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

JavaScript

Tags

copy-paste, dead-code, reliability

Description

Reports a conditional expression cond ? a : b where the two branches are textually identical:

const x = ready ? 1 : 1;
const y = ok    ? doStuff() : doStuff();

The condition is evaluated for nothing — both branches produce the same result.

Rationale

A ternary that returns the same value in both branches almost always means one of:

  • the developer copy-pasted one branch and forgot to change it

  • the condition was left over after one branch was simplified, and now the whole expression is dead

Either way the conditional misleads readers, who reasonably assume ?: means the two sides differ.

Remediation

Replace the ternary with the branch itself:

const x = 1;
const y = doStuff();

If the branches were supposed to differ, fix whichever one is wrong:

const x = ready ? 1 : 0;

Notes

The rule fires only when the textual source of the two branches is identical (after trimming). Side effects in the condition are not considered: dropping the ternary may change behaviour if the condition is someFunction(), so the suggested fix above assumes a side-effect-free condition.

References