Epic沒有在Redux-Observable中返回流

Question

我正在測試使用帶有side-project的redux-observable並且我反復Uncaught TypeError: combineEpics: one of the provided Epics "handleSearchEpic" does not return a stream. Double check you're not missing a return statement!這個問題： 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!

我在網上引用了redux可觀察文檔和其他幾個例子，但我無法確定我可能缺少的內容。 以下是我的行為和有問題的史詩。

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
);

這是應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史詩是一個帶有塊的箭頭函數，但實際上並沒有返回流。

壞

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))
}

隱含的回報？

或者，您可以刪除塊並使用隱式返回，這可能是您的意圖嗎？

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

---

一個非常常見的錯誤，這就是為什么我添加了您提供的錯誤消息，但它似乎並沒有使解決方案可理解。 有關如何改進錯誤消息的任何建議嗎？

combineEpics：提供的Epics之一“handleSearchEpic”不返回流。 仔細檢查你沒有錯過退貨聲明！