Diagnosing unnecessary re-renders with subscribeWithSelector middleware

Goal

Measure whether a component re-rendering on every store update is caused by an unstable selector reference, a missing shallow equality function, or genuinely changing state — before applying any optimization.

Constraints and uncertainty

The subscribeWithSelector middleware exposes store.subscribe(selector, listener, options) for slice-based subscriptions, yet the default Object.is comparison treats each inline object selector as a new reference. A component selecting {a: s.a, b: s.b} will re-render on any state change unless a custom equality function is supplied. The same store can be exercised in plain Node via store.subscribe without mounting React components, but the most reliable signal — Profiler render counts, selector logging, or listener invocation counts — depends on the environment and the shape of the selected slice.

Questions

1. Which measurement approach (React DevTools Profiler, inline selector logging, or subscribe listener counting) gives the clearest signal for a given selector shape?
2. How can a Node-only test verify that a selector with shallow equality fires only when the selected slice actually changes?
3. At what object size does the cost of shallow comparison outweigh the re-renders it prevents?