javascript - 无法读取未定义的属性 'then'

Question

所以我正在使用 react + redux，并且继续收到以下错误:“无法读取未定义的属性‘then’”。由于某种原因， promise 没有被退回。我对使用 redux thunk 也特别陌生。

reducer

import { merge } from 'lodash';
import  * as APIutil  from '../util/articles_api_util';


import {
  ArticleConstants
} from '../actions/article_actions';

const ArticlesReducer = (state = {}, action) => {
  switch (action.type) {
    case ArticleConstants.RECEIVE_ALL_ARTICLES:
    debugger
    return merge({}, action.articles);
    default:
      return state;
  }
};

export default ArticlesReducer;

商店

import { createStore, applyMiddleware } from 'redux';
import RootReducer from '../reducers/root_reducer';
import thunk from 'redux-thunk';

import  * as APIUtil  from '../util/articles_api_util';

export const ArticleConstants = {
    RECEIVE_ALL_ARTICLES: "RECEIVE_ALL_ARTICLES",
    REQUEST_ALL_ARTICLES: "REQUEST_ALL_ARTICLES"
}

Action

export function fetchArticles() {
  return function(dispatch) {
    return APIUtil.fetchArticles().then(articles => {
      dispatch(receiveAllArticles(articles));
    }).catch(error => {
      throw(error);
    });
  };
}


export const requestAllArticles= () => ({
    type: REQUEST_ALL_ARTICLES
});


export const receiveAllArticles = articles => ({
    type: RECEIVE_ALL_ARTICLES,
    articles
});

    const configureStore = (preloadedState = {}) => (
      createStore(
        RootReducer,
        preloadedState,
        applyMiddleware(thunk)
      )
    );


    export default configureStore;

APIUtil

export const fetchArticles = (success) => {
  $.ajax({
        method: 'GET',
        url: `/api/articles`,
        success,
        error: ()=> (
        console.log("Invalid Article")
      )
    });
};

Answer 1

如果您不使用大括号，箭头函数只会执行隐式 return。只要包含大括号，就定义了一个函数体，需要显式返回一个值。

您的 fetchArticles 函数被编写为带有花括号的箭头函数。但是，您并未明确返回 $.ajax() 调用的结果。因此，该函数的返回值为 undefined，并且没有返回您可以链接的 promise 。