Appendix

Appendix A – Skipping the dispatch

We say that not all dispatched states end up with a change. But actually, not all dispatches end up with a successful dispatch. When a mouse clicks, it goes into the dispatch function. It has a special pathway, and when you hit that condition and find out there's no state change, it can return early without performing a dispatch:

function dispatchAction(fiber, queue, action) {
  ...
    
  if (NoWorkUnderFiber) {
    const currentState = queue.lastRenderedState
    const newState = typeof action === 'function' 
      ? action(currentState) : action
    if (Object.is(newState, currentState)) {
      return
    }
  }
  scheduleUpdateOnFiber(fiber)
}

In the preceding dispatchAction function, a new state is computed...