React-redux: Clarification required on batch() documentation

[soulprovidr]

Hi all -- first of all, thank you for your work on this library. I have a question based on an example from the documentation I ran last night.

What is the current behavior?

According to the 7.2 documentation for batch(), this code should result in two renders if batch() is not used:

import { batch } from 'react-redux'

function myThunk() {
  return (dispatch, getState) => {
    // should only result in one combined re-render, not two
    batch(() => {
      dispatch(increment())
      dispatch(increment())
    })
  }
}

However, when I removed batch() in this case, the code still resulted in one render.

You can see that in action here with the incrementByTwo() action creator:

https://codesandbox.io/s/goofy-pare-6nncg

What is the expected behavior?

Based on the documentation, I would expect removing batch() in this circumstance to result in two renders. Can anyone advise me as to why this is not happening?

Thanks!

[markerikson]

Because those thunks are running synchronously inside of a React event handler. Thus, they are _already_ running inside of a batch() call, albeit one that's internal to React's own event handling.

See my post at https://blog.isquaredsoftware.com/2020/05/blogged-answers-a-mostly-complete-guide-to-react-rendering-behavior/#render-batching-and-timing for a complete explanation of how React handles batching.