Unused Local Variable

ID

javascript.unused_local_variable

Severity

low

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Code Smell

Language

JavaScript

Tags

CWE:563, code-style, dead-code

Description

Reports var, let or const declarations whose binding is never referenced after declaration. Plain identifier bindings only — destructuring patterns are out of scope for this version of the rule.

Rationale

// Bad — declared and forgotten.
function dead() {
  const cache = new Map();
  return 42;
}

// Bad — refactor leftover.
function processed(rows) {
  const total = rows.length;
  return rows.map(format);
}

Unused bindings clutter scope, mislead readers about what the function uses, and often hide that an earlier branch was deleted but its setup wasn’t.

Remediation

Delete the declaration. When the right-hand side has a side effect that the function still needs, hoist that call to a statement of its own:

// Good — keep the side effect, drop the unused binding.
function withSideEffect() {
  cleanupQueue();          // was: const cleaned = cleanupQueue();
  return 42;
}

Exclusions:

  • Names starting with _ are treated as intentionally unused (placeholder pattern).

  • Declarations inside an export are consumed by other modules — they are not flagged even when no local code references them.

References