Multiple Selection and Add/Delete Components using Effects

This app uses custom hooks for two purposes:

  1. To resolve the earlier bug. An effect is run whenever cities changes. This effect ensures that the invariant selCities ⊆ cities remains true.
  2. If the query parameter doLog is specified, then all mounts, unmounts and renders on all components are logged to the console using a effect encapsulated within a custom hook useLog().

      3. App