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Exporting a component inside an asynchronous function

I use to react and nearby. I need to export a component, but I don't have the right to put it in a function
function Index(){
}
export default Index
You must receive a request, but you can only write to a variable if the function is asynchronous.
I had to create a wrapper
async function asy(){
const data = await fetchData()
function Index(){
}
export default Index
}
asy().then(r => r);
Now I can't export the component.
I found a different solution, but it doesn't work either.
function Index(){
return async function asy(){
//async function.
const data = await fetchData()
return <React.Fragment/>
}
}
export default Index

I Don't think I fully understand your question but here is what I understood,
You want to return a component after making an async request to retrieve data.
I would go for something like this:
function Index() {
const [data, setData] = React.useState(null);
retrieveData = async () => {
// Retrieve your data
setData(retrievedData);
}
useEffect(() => {
retrieveData();
}, [])
if (data != null) {
return <YourComponent />
} else {
return null
}
}
This code will call the retrieveData function each time this component is mounted

How to convert functional component using hooks to class component

I'm trying to challenge myself to convert my course project that uses hooks into the same project but without having to use hooks in order to learn more about how to do things with class components. Currently, I need help figuring out how to replicate the useCallback hook within a normal class component. Here is how it is used in the app.
export const useMovieFetch = movieId => {
const [state, setState] = useState({});
const [loading, setLoading] = useState(true);
const [error, setError] = useState(false);
const fetchData = useCallback(async () => {
setError(false);
setLoading(true);
try{
const endpoint = `${API_URL}movie/${movieId}?api_key=${API_KEY}`;
const result = await(await fetch(endpoint)).json();
const creditsEndpoint = `${API_URL}movie/${movieId}/credits?api_key=${API_KEY}`;
const creditsResult = await (await fetch(creditsEndpoint)).json();
const directors = creditsResult.crew.filter(member => member.job === 'Director');
setState({
...result,
actors: creditsResult.cast,
directors
});
}catch(error){
setError(true);
console.log(error);
}
setLoading(false);
}, [movieId])
useEffect(() => {
if(localStorage[movieId]){
// console.log("grabbing from localStorage");
setState(JSON.parse(localStorage[movieId]));
setLoading(false);
}else{
// console.log("Grabbing from API");
fetchData();
}
}, [fetchData, movieId])
useEffect(() => {
localStorage.setItem(movieId, JSON.stringify(state));
}, [movieId, state])
return [state, loading, error]
}
I understand how to replicate other hooks such as useState and useEffect but I'm struggling to find the answer for the alternative to useCallback. Thank you for any effort put into this question.

TL;DR
In your specific example useCallback is used to generate a referentially-maintained property to pass along to another component as a prop. You do that by just creating a bound method (you don't have to worry about dependencies like you do with hooks, because all the dependencies are maintained on your instance as props or state.
class Movie extends Component {
constructor() {
this.state = {
loading:true,
error:false,
}
}
fetchMovie() {
this.setState({error:false,loading:true});
try {
// await fetch
this.setState({
...
})
} catch(error) {
this.setState({error});
}
}
fetchMovieProp = this.fetchMovie.bind(this); //<- this line is essentially "useCallback" for a class component
render() {
return <SomeOtherComponent fetchMovie={this.fetchMovieProp}/>
}
}
A bit more about hooks on functional vs class components
The beautiful thing about useCallback is, to implement it on a class component, just declare an instance property that is a function (bound to the instance) and you're done.
The purpose of useCallback is referential integrity so, basically, your React.memo's and React.PureComponent's will work properly.
const MyComponent = () => {
const myCallback = () => { ... do something };
return <SomeOtherComponent myCallback={myCallback}/> // every time `MyComponent` renders it will pass a new prop called `myCallback` to `SomeOtherComponent`
}
const MyComponent = () => {
const myCallback = useCallback(() => { ... do something },[...dependencies]);
return <SomeOtherComponent myCallback={myCallback}/> // every time `MyComponent` renders it will pass THE SAME callback to `SomeOtherComponent` UNLESS one of the dependencies changed
}
To replicate useCallback in class components you don't have to do anything:
class MyComponent extends Component {
method() { ... do something }
myCallback = this.method.bind(this); <- this is essentially `useCallback`
render() {
return <SomeOtherComponent myCallback={this.myCallback}/> // same referential integrity as `useCallback`
}
}
THE BIG ONE LINER
You'll find that hooks in react are just a mechanism to create instance variables (hint: the "instance" is a Fiber) when all you have is a function.

You can replicate the behavior ofuseCallback by using a memorized function for the given input(eg: movieId)
You can use lodash method
for more in-depth understanding check here

Re-rendering react component after clicking Like button (with Redux)

I have the following React component that shows all the users posts through the "renderPosts" method. Below it there's a like/unlike button on whether the currently logged in user has liked the post.
However, when I click on the like button, the component does not re-render in order for the "renderPosts" method to create an unlike button and the "like string" is modified as expected. Only when I go to another component and then come back to this component does the unlike button display and vice versa.
Is there anyway that I could fix this with Redux in my app? I tried this.forceUpdate after the onClick event but still does not work...
Also I tried creating a new Reducer called "likers", according to robinsax which basically get the array of users who like a particular post and imported it as props into the component but got
"this.props.likers.includes(currentUser)" is not a function
When the app first gets to the main page (PostIndex), probably because this.props.likers is still an empty object returned from reducer
Here is the code for my action creator:
export function likePost(username,postId) {
// body...
const request = {
username,
postId
}
const post = axios.post(`${ROOT_URL}/likePost`,request);
return{
type: LIKE_POST,
payload: post
}
}
export function unlikePost(username,postId){
const request = {
username,
postId
}
const post = axios.post(`${ROOT_URL}/unlikePost`,request);
return{
type: UNLIKE_POST,
payload: post
}
}
And this is my reducer:
import {LIKE_POST,UNLIKE_POST} from '../actions/index.js';
export default function(state = {},action){
switch(action.type){
case LIKE_POST:
const likers = action.payload.data.likedBy;
console.log(likers);
return likers;
case UNLIKE_POST:
const unlikers = action.payload.data.likedBy;
console.log(unlikers);
return unlikers;
default:
return state;
}
}
I would really appreciate any help since I'm a beginner
import { fetchPosts } from "../actions/";
import { likePost } from "../actions/";
import { unlikePost } from "../actions/";
class PostsIndex extends Component {
componentDidMount() {
this.props.fetchPosts();
}
renderPost() {
const currentUser = Object.values(this.props.users)[0].username;
return _.map(this.props.posts, post => {
return (
<li className="list-group-item">
<Link to={`/user/${post.username}`}>
Poster: {post.username}
</Link>
<br />
Created At: {post.createdAt}, near {post.location}
<br />
<Link to={`/posts/${post._id}`}>{post.title}</Link>
<br />
//error here, with this.props.likers being an
//array
{!this.props.likers.includes(currentUser) ? (
<Button
onClick={() => this.props.likePost(currentUser,post._id)}
bsStyle="success"
>
Like
</Button>
) : (
<Button
onClick={() => this.props.unlikePost(currentUser,post._id)}
bsStyle="warning"
>
Unlike
</Button>
)}{" "}
{post.likedBy.length === 1
? `${post.likedBy[0]} likes this`
: `${post.likedBy.length} people like this`}
</li>
);
});
}
function mapStateToProps(state) {
return {
posts: state.posts,
users: state.users,
likers: state.likers
};
}
}

Seems like the like/unlike post functionality isn't causing anything in your state or props to change, so the component doesn't re-render.
You should change the data structure you're storing so that the value of post.likedBy.includes(currentUser) is included in one of those, or forceUpdate() the component after the likePost and unlikePost calls.
Please do it the first way so I can sleep at night. Having a component's render() be affected by things not in its props or state defeats the purpose of using React.

As noted in other answers, you need to use redux-thunk or redux-saga to make async calls that update you reducer. I personally prefer redux-saga. Here's is a basic implementation of React, Redux, and Redux-Saga.
Redux-Saga uses JavaScript generator functions and yield to accomplish the goal of handling async calls.
Below you'll see a lot of familiar React-Redux code, the key parts of Redux-Saga are as follows:
watchRequest - A generator function that maps dispatch actions to generator functions
loadTodo - A generator function called from watchRequest to yield a value from an async call and dispatch an action for the reducer
getTodoAPI - A regular function that makes a fetch request
applyMiddleware - from Redux is used to connect Redux-Saga with createStore
const { applyMiddleware, createStore } = Redux;
const createSagaMiddleware = ReduxSaga.default;
const { put, call } = ReduxSaga.effects;
const { takeLatest } = ReduxSaga;
const { connect, Provider } = ReactRedux;
// API Call
const getTodoAPI = () => {
return fetch('https://jsonplaceholder.typicode.com/todos/1')
.then(response => {
return response.json()
.then(response => response);
})
.catch(error => {
throw error;
})
};
// Reducer
const userReducer = (state = {}, action) => {
switch (action.type) {
case 'LOAD_TODO_SUCCESS':
return action.todo;
default:
return state;
}
};
// Sagas, which are generator functions
// Note: the asterix
function* loadTodo() {
try {
const todo = yield call(getTodoAPI);
yield put({type: 'LOAD_TODO_SUCCESS', todo});
} catch (error) {
throw error;
}
}
// Redux-Saga uses generator functions,
// which are basically watchers to wait for an action
function* watchRequest() {
yield* takeLatest('LOAD_TODO_REQUEST', loadTodo);
}
class App extends React.Component {
render() {
const { data } = this.props;
return (
<div>
<button onClick={() => this.props.getTodo()}>Load Data</button>
{data ?
<p>data: {JSON.stringify(data)}</p>
: null
}
</div>
)
}
}
// Setup React-Redux and Connect Redux-Saga
const sagaMiddleware = createSagaMiddleware();
const store = createStore(userReducer, applyMiddleware(sagaMiddleware));
sagaMiddleware.run(watchRequest);
// Your regular React-Redux stuff
const mapStateToProps = (state) => ({ data: state }); // Map the store's state to component's props
const mapDispatchToProps = (dispatch) => ({ getTodo: () => dispatch({type: 'LOAD_TODO_REQUEST'}) }) // wrap action creator with dispatch method
const RootComponent = connect(mapStateToProps, mapDispatchToProps)(App);
ReactDOM.render(
<Provider store={store}>
<RootComponent />
</Provider>,
document.getElementById('root')
);
<script src="https://npmcdn.com/babel-regenerator-runtime#6.3.13/runtime.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/redux/4.0.1/redux.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-redux/6.0.0/react-redux.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/redux-saga/0.16.2/redux-saga.min.js"></script>
<div id="root"></div>

You need to use redux-thunk middleware in order to use async actions.
First, add redux-thunk while creating store like
import thunk from 'redux-thunk';
const store = createStore(
rootReducer,
applyMiddleware(thunk)
);
then change your method like this
export function likePost(username,postId) {
return function(dispatch) {
// body...
const request = {
username,
postId
}
axios.post(`${ROOT_URL}/likePost`,request)
.then(res => {
dispatch({
type: LIKE_POST,
payload: res
});
});
}
}
and now in your component after mapStateToProps, define mapDispatchToProps,
const mapDispatchToProps = dispatch => {
return {
likePost: (currentUser,postId) => dispatch(likePost(currentUser, postId)),
// same goes for "unlike" function
}
}
export default connect(mapStateToProps, mapDispatchToProps)(PostsIndex);

The problem is in your action creator.
export function likePost(username,postId) {
// body...
const request = {
username,
postId
}
// this is an async call
const post = axios.post(`${ROOT_URL}/likePost`,request);
// next line will execute before the above async call is returned
return{
type: LIKE_POST,
payload: post
}
}
Because of that your state is likely never updated and stays in the initial value.
You would need to use either redux-thunk or redux-saga to work with async actions.

As they say use redux-thunk or redux-saga. If your new to redux I prefer redux-thunk because it's easy to learn than redux-saga. You can rewrite your code like this
export function likePost(username,postId) {
// body...
const request = {
username,
postId
}
const post = axios.post(`${ROOT_URL}/likePost`,request);
return dispatch => {
post.then(res => {
dispatch(anotherAction) //it can be the action to update state
});
}
}

How to use enzyme to test component with asyn lifecircle function?

I'm using jest and enzyme to test my component. And in this component, I will request data in componentDidMount, and then it will render view with the data.
class App extends React.Component {
async componentDidMount() {
const data = await getData(); // send a request to server to get data
this.setState({
name: data.name,
})
}
render() {
return (
<div>{this.state.name}</div>
)
}
}
It is a very simple component, just only use async function in componentDidMount, and get data width a async way, not callback. But, I don't know how to test this component.
I'd like write test code like this
it('render', async () => {
const container = mount(
<App />
);
const instance = container.instance();
console.log(instanct.state.name); // of course, state.name is undefined, but I want in this place, the state.name can be 'qyt'
});

I created a demo project on Github here.
The solution I went with was to mock the getData module:
let mockPromise;
jest.mock("./getData", () => {
return jest.fn(() => {
mockPromise = Promise.resolve({ name: "Spider man" });
return mockPromise;
});
});
Then I returned the mockPromise in my test. Jest will wait for the promise to resolve before completing the test.
it("renders without crashing", () => {
const wrapper = shallow(<App />);
return mockPromise.then((a) => {
wrapper.update();
expect(wrapper.html()).toEqual(`<h1>Name: Spider man</h1>`);
});
});

Thunk Action Body not being Invoked

My thunk action doesn't seem to be running through its core logic. I tall the thunk action from componentDidMount but it doesn't in turn cause this to run: const response = await findOne(id).
Also, I thought I didn't need to explicitely pass dispatch as a prop to mapDispatchToProps if using redux-thunk, I thought that the way I have my thunk setup is that dispatch is available already to the thunk? And I've used other actions like this and it's worked fine, why not this one?
Thunk Action
export function fetchCompany(id) {
return async (dispatch) => {
try {
const response = await findOne(id)
if(response && response.body) {
const company = response.body
dispatch(companyReceived(company))
}
} catch(err) {
console.log("failed request in authenticate thunk action")
console.log(`error details: ${err.status} /n ${err}`)
}
}
}
Container
......
import { fetchCompany } from '../../client/actions/company/CompanyAsyncActions'
class InterviewContainer extends Component {
async componentDidMount() {
await fetchCompany(this.props.params.companyId)
}
render(){
return (this.props.company && <Interview className='ft-interview' company={this.props.company} />)
}
}
const mapStateToProps = state => ({
company: state.company.company
})
const mapDispatchToProps = {
fetchCompany: fetchCompany
}
export default connect(mapStateToProps, mapDispatchToProps)(InterviewContainer)
In the past, I haven't passed (dispatch) as a prop to mapDispatchToProps and it worked fine. But I see everyone else is doing so. How was my code working in the past if I wasn't doing that? And why isn't this working this time around in the example above?
Taking a look at another async action thunk container and call example, this is working completely fine, and I'm calling it the same way in another container
container
class HomePageContainer extends Component {
constructor(){
super()
}
async componentDidMount() {
await this.props.fetchFeaturedCompanies()
await this.props.fetchCompanies()
await this.props.fetchCountries()
}
render(){
return (<HomePage className='ft-homepage'
featuredCompanies={this.props.featuredCompanies}
countries={this.props.countries}
companies={this.props.companies}
/>)
}
}
const mapStateToProps = state => ({
countries: state.country.countries,
companies: state.company.companies,
featuredCompanies: state.company.featuredCompanies
})
const mapDispatchToProps = {
fetchCountries: fetchCountries,
fetchCompanies: fetchCompanies,
fetchFeaturedCompanies: fetchFeaturedCompanies
}
export default connect(mapStateToProps, mapDispatchToProps)(HomePageContainer)
thunk action
export function fetchCompanies() {
return async (dispatch, getState) => {
const response = await find()
if(response && response.body) {
const companies = response.body
dispatch(companiesReceived(companies))
}
}
}

In componentDidMount of InterviewContainer you're accidentally calling the imported fetchCompany, instead of this.props.fetchCompany.