No duplicate packages at conflicting versions

Two major versions of the same package installed simultaneously means two copies of that code running in your application. For React, this causes hooks to fail silently or crash at runtime because each copy maintains its own internal state. For validation libraries, it means validators from one version cannot accept instances created by the other. The ISO 25010 maintainability characteristic is directly degraded: duplicate packages make the dependency graph non-deterministic from a debugging standpoint and inflate install size without adding functionality. Duplicate packages most commonly appear when you upgrade a direct dependency but a transitive parent still pins the old major — the resolution is visible in the lock file but invisible at the source code level.

Diagnose which package requires the old version:

npm ls react

If the old version comes from a third-party dependency you cannot upgrade immediately, force resolution using overrides:

// package.json
"overrides": {
  "react": "^18.0.0"
}

Test thoroughly after applying the override — forcing a newer major can break packages that genuinely rely on the older API. The correct long-term fix is upgrading or replacing the package that pins the old version.