Epic没有在Redux-Observable中返回流

Question

我正在测试使用带有side-project的redux-observable并且我反复Uncaught TypeError: combineEpics: one of the provided Epics "handleSearchEpic" does not return a stream. Double check you're not missing a return statement!这个问题： Uncaught TypeError: combineEpics: one of the provided Epics "handleSearchEpic" does not return a stream. Double check you're not missing a return statement! Uncaught TypeError: combineEpics: one of the provided Epics "handleSearchEpic" does not return a stream. Double check you're not missing a return statement!

我在网上引用了redux可观察文档和其他几个例子，但我无法确定我可能缺少的内容。 以下是我的行为和有问题的史诗。

export const searchContent = query => {
  return {
    type: SEARCH_CONTENT,
    query
  }
}

const returnSearchContent = searchResults => {
  return function(dispatch) {
    dispatch({
      type: RETURN_SEARCH_CONTENT,
      searchResults
    });
  }
}

// Epics
export const handleSearchEpic = action$ => {
  action$.ofType(SEARCH_CONTENT)
    .mergeMap(action => axios.get(`...SOME_API_ENDPOINT`))
    .map(res => returnSearchContent(res))
}

export const rootEpic = combineEpics(
  handleSearchEpic
);

这是应用程序的根和商店配置：

const epicMiddleware = createEpicMiddleware(rootEpic);
const store = createStore(Reducer, applyMiddleware(epicMiddleware));

ReactDOM.render(
  <Provider store={store}>
    <App />
  </Provider>,
  document.getElementById('root')
);

Answer 1

你的handleSearchEpic史诗是一个带有块的箭头函数，但实际上并没有返回流。

坏

export const handleSearchEpic = action$ => { // <-- start of block
  // vvvvvvv missing return
  action$.ofType(SEARCH_CONTENT)
    .mergeMap(action => axios.get(`...SOME_API_ENDPOINT`))
    .map(res => returnSearchContent(res))
} // <-- end of block

好

export const handleSearchEpic = action$ => {
  return action$.ofType(SEARCH_CONTENT)
    .mergeMap(action => axios.get(`...SOME_API_ENDPOINT`))
    .map(res => returnSearchContent(res))
}

隐含的回报？

或者，您可以删除块并使用隐式返回，这可能是您的意图吗？

export const handleSearchEpic = action$ => // <--- no block
  action$.ofType(SEARCH_CONTENT)
    .mergeMap(action => axios.get(`...SOME_API_ENDPOINT`))
    .map(res => returnSearchContent(res));

---

一个非常常见的错误，这就是为什么我添加了您提供的错误消息，但它似乎并没有使解决方案可理解。 有关如何改进错误消息的任何建议吗？

combineEpics：提供的Epics之一“handleSearchEpic”不返回流。 仔细检查你没有错过退货声明！