Wait for a redux action to finish dispatching

You can always wrap appendItem into a promise and pass dispatch as an argument to it

const appendItem = (item, dispatch) => new Promise((resolve, reject) => {
  // do anything here
  dispatch(<your-action>);
  resolve();
}

Then you can call it like this from scrolltoNextItem

export function scrolltoNextItem(item) {
  return (dispatch, getState) => {
    appendItem(Item, dispatch).then(() => {
      dispatch(
        scrollToNextIndex(
          getState().items.length - 1
        )
      )
    })
  }
}