reactjs - 无法读取 Redux thunk 操作上未定义的属性 'then'

Question

我是 React、Redux 和 Thunk 的新手，并且一直在关注有关该主题的教程，最近 Building Applications with React and Redux in ES6在 Pluralsight 上。我已将本教程从 ES6 转换为 Typescript 3，并将 React v3 转换为 React v4。

我遇到了很多可以按照此模式解决的问题(尤其是与路由相关的任何问题)，但我遇到了一个无法解决的问题。来自各种来源公司Cannot read property '.then' of undefined when testing async action creators with redux and react听起来我不能在返回 void 的函数上使用 .then() 函数，但它是一个异步函数(应该)返回一个 promise ，但智能感知却另有说法。代码如下。

saveCourse = (event: any) => {
    event.preventDefault();
    this.props.actions.saveCourse(this.state.course)
        .then(this.setState({ fireRedirect: true }));
}

上面的代码位于我的组件上，props.actions 通过 mapStateToProps 连接到 redux 存储，并且在单击按钮时调用此函数。上面这个函数的 .then() 出现了错误。该函数调用下面的操作

export const saveCourse = (course: Course) => {
    return (dispatch: any, getState: any) => {
        dispatch(beginAjaxCall());
        courseApi.saveCourse(course).then((savedCourse: Course) => {
            course.id ? dispatch(updateCourseSuccess(savedCourse)) :
                dispatch(createCourseSuccess(savedCourse));
        }).catch(error => {
            throw (error);
        });
    }
}

上面的操作是异步调用，这里的 .then() 没有错误，但 VS Code 说整个 saveCourse 函数返回 void。

从教程来看，确实没有任何差异可以产生影响(箭头函数而不是常规函数等...)，所以我想知道我缺少的版本之间是否存在模糊的变化，但不知道在哪里看看，可能会遗漏一些基本的东西。谁能明白为什么我不能在 saveCourse() 函数上执行 .then() 吗？

如果您需要更多信息，请告诉我。

编辑:courseApi 只是一个模拟 api，代码如下。

import delay from './delay';

const courses = [
{
    id: "react-flux-building-applications",
    title: "Building Applications in React and Flux",
    watchHref: "http://www.pluralsight.com/courses/react-flux-building-applications",
    authorId: "cory-house",
    length: "5:08",
    category: "JavaScript"
},
{
    id: "clean-code",
    title: "Clean Code: Writing Code for Humans",
    watchHref: "http://www.pluralsight.com/courses/writing-clean-code-humans",
    authorId: "cory-house",
    length: "3:10",
    category: "Software Practices"
},
{
    id: "architecture",
    title: "Architecting Applications for the Real World",
    watchHref: "http://www.pluralsight.com/courses/architecting-applications-dotnet",
    authorId: "cory-house",
    length: "2:52",
    category: "Software Architecture"
},
{
    id: "career-reboot-for-developer-mind",
    title: "Becoming an Outlier: Reprogramming the Developer Mind",
    watchHref: "http://www.pluralsight.com/courses/career-reboot-for-developer-mind",
    authorId: "cory-house",
    length: "2:30",
    category: "Career"
},
{
    id: "web-components-shadow-dom",
    title: "Web Component Fundamentals",
    watchHref: "http://www.pluralsight.com/courses/web-components-shadow-dom",
    authorId: "cory-house",
    length: "5:10",
    category: "HTML5"
}
];

function replaceAll(str: any, find: any, replace: any) {
return str.replace(new RegExp(find, 'g'), replace);
}

//This would be performed on the server in a real app. Just stubbing in.
const generateId = (course: any) => {
return replaceAll(course.title, ' ', '-');
};

class CourseApi {
static getAllCourses() {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve(Object.assign([], courses));
        }, delay);
    });
}

static saveCourse(course: any) {
    course = Object.assign({}, course); // to avoid manipulating object         passed in.
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            // Simulate server-side validation
            const minCourseTitleLength = 1;
            if (course.title.length < minCourseTitleLength) {
                reject(`Title must be at least ${minCourseTitleLength} characters.`);
            }

            if (course.id) {
                const existingCourseIndex = courses.findIndex(a => a.id == course.id);
                courses.splice(existingCourseIndex, 1, course);
            } else {
                //Just simulating creation here.
                //The server would generate ids and watchHref's for new courses in a real app.
                //Cloning so copy returned is passed by value rather than by reference.
                course.id = generateId(course);
                course.watchHref = `http://www.pluralsight.com/courses/${course.id}`;
                courses.push(course);
            }

            resolve(course);
        }, delay);
    });
}

static deleteCourse(courseId: any) {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            const indexOfCourseToDelete = courses.findIndex(course =>
                course.id == courseId
            );
            courses.splice(indexOfCourseToDelete, 1);
            resolve();
        }, delay);
    });
}
}

export default CourseApi;

Answer 1

您遇到的问题是您没有返回 Action Creator 中的 promise 。

在这里查看 redux-thunk 的示例:

https://github.com/reduxjs/redux-thunk

function makeASandwichWithSecretSauce(forPerson) {

  // Invert control!
  // Return a function that accepts `dispatch` so we can dispatch later.
  // Thunk middleware knows how to turn thunk async actions into actions.

  return function (dispatch) {
    return fetchSecretSauce().then(
      sauce => dispatch(makeASandwich(forPerson, sauce)),
      error => dispatch(apologize('The Sandwich Shop', forPerson, error))
    );
  };
}

他们正在返回由 fetchSecretSauce 生成的 promise 。

您需要在示例中类似地返回 promise :

export const saveCourse = (course: Course) => {
    return (dispatch: any, getState: any) => {
        dispatch(beginAjaxCall());
        return courseApi.saveCourse(course).then((savedCourse: Course) => {
            course.id ? dispatch(updateCourseSuccess(savedCourse)) :
                dispatch(createCourseSuccess(savedCourse));
        }).catch(error => {
            throw (error);
        });
    }
}