No dead code — unused exports, components, and functions

Dead code — unused components, unexported utility modules, unreachable API routes — imposes a cognitive tax on every developer who reads the codebase. Is this file used? Was it intentionally removed? Should I modify it or ignore it? ISO 25010 maintainability.analysability degrades as dead code accumulates. It also creates false positives in security reviews: an unused API route with no authentication looks like a security gap even if nothing calls it. AI-generated codebases accumulate dead code across sessions as earlier implementations get replaced without cleanup.

Find unused exports and modules automatically:

npx ts-prune    # finds unused TypeScript exports
# or
npx knip        # comprehensive dead code detection

Before deleting, confirm with git log that code wasn't recently added and is genuinely unreachable. Prevent accumulation with:

"no-unused-vars": ["warn", { "vars": "all", "args": "after-used" }]

Delete confirmed dead code and commit with a descriptive message — git history preserves it if recovery is ever needed.

• ID: no-dead-code

• Severity: medium

• What to look for: Look for code that is defined but never called or imported. Common patterns:

  • Exported functions or components in lib/ or utils/ that are never imported anywhere
  • React components defined but never used in any route or parent component
  • API routes that are never called from the frontend
  • TypeScript types or interfaces that are defined but never referenced
  • Entire files that aren't imported anywhere and aren't entry points

  Focus on non-trivial code (>10 lines). Single unused utility functions are acceptable; entire unused modules are not. Check if eslint-plugin-unused-imports or the no-unused-vars rule is configured to catch this.

• Pass criteria: Count all exported functions, components, and modules in src/. No entire unused modules or components found. No more than 2 minor unused exports are acceptable if an ESLint rule would catch them. Report the count: "X of Y exports are actively used."

• Fail criteria: Two or more substantial code units (components, utility modules, or API routes with over 10 lines) are defined but never imported or called anywhere.

• Skip (N/A) when: The project has fewer than 10 source files — not enough for meaningful dead code analysis. Signal: fewer than 10 distinct source files.

• Detail on fail: "Dead code found: components/OldDashboard.tsx (80 lines, never imported), lib/legacy-auth.ts (120 lines, all exports unused), app/api/v1/deprecated-endpoint/route.ts (never called from frontend or tests)." or "15 exported functions in lib/utils.ts have no importers across the codebase."

• Remediation: Dead code imposes a mental tax — developers must read and understand code that does nothing. It also creates false positives in security reviews and makes refactoring riskier (is this code truly unused, or did I miss an import?).

  To find unused exports automatically:

  npx ts-prune  # finds unused TypeScript exports
  # or
  npx knip      # comprehensive dead code detection
  

  Remove confirmed dead code and add an ESLint rule to prevent accumulation:

  "no-unused-vars": ["warn", { "vars": "all", "args": "after-used" }]
  

  Before removing, confirm with git history that the code wasn't recently added and is actually unreachable (not just indirectly referenced through dynamic imports).