为什么使用redux-thunk时，内部函数返回某些内容？

Question

我在使用redux-thunk时经常看到代码，内部函数返回某些内容，例如the official Redux async example：

The code：

const fetchPosts = subreddit => dispatch => {
  dispatch(requestPosts(subreddit))
  return fetch(`https://www.reddit.com/r/${subreddit}.json`)
    .then(response => response.json())
    .then(json => dispatch(receivePosts(subreddit, json)))
}

const shouldFetchPosts = (state, subreddit) => {
  // return true or false
}

export const fetchPostsIfNeeded = subreddit => (dispatch, getState) => {
  if (shouldFetchPosts(getState(), subreddit)) {
    return dispatch(fetchPosts(subreddit))
  }
}

所以fetchPostsIfNeeded()是重击，fetchPosts()也是如此。它们都返回一个函数，并且函数也返回某些东西。现在，该功能实际上是由中间件调用的，我不认为会使用返回的值。那么，为什么thunk内部的内部函数会继续返回某些东西，而不仅仅是调用它？该代码可能是：

const fetchPosts = subreddit => dispatch => {
  dispatch(requestPosts(subreddit))
  fetch(`https://www.reddit.com/r/${subreddit}.json`)
    .then(response => response.json())
    .then(json => dispatch(receivePosts(subreddit, json)))
}

const shouldFetchPosts = (state, subreddit) => {
  // return true or false
}

export const fetchPostsIfNeeded = subreddit => (dispatch, getState) => {
  if (shouldFetchPosts(getState(), subreddit)) {
    dispatch(fetchPosts(subreddit))
  }
}

Answer 1

[它返回一个promise，允许您在then链中添加回调，并在例如获取subredit帖子时执行某些操作。

export const fetchPostsIfNeeded = subreddit => (dispatch, getState) => {
  if (shouldFetchPosts(getState(), subreddit)) {
    dispatch(fetchPosts(subreddit)).then(() => doSomething());
  }
}