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How can I assign data from Http response in const Component?

My goal is to ultimately create add a shopping cart functionality using context API. In order to do so I need to get the products from my database and store it in an array.
Currently, the challenge I'm facing is how to retrieve the data from the axios response and store it in a variable that will be passed on within a const component. Apparently, the issue is that the variable gets passed to the child before the Axios response is complete.
I tried using the await keyword, but got an error regarding not being in an async function. Hence, I tried plugging the async keyword but that didn't work as it yielded errors.
I was able to retrieve data from axios within class components with success, however, I am unable to do so in these const.
Here is my code:
Context.js
import { createContext, useContext, useReducer } from "react";
import React from "react";
import ProductService from "../services/ProductService";
import { cartReducer } from "./Reducers";
const Cart = createContext();
const Context = ({ children }) => {
let products = [];
console.log("part1", products);
ProductService.getAllProducts().then((res) => {
products = res.data; //Also tried setState({ products : res.data})
console.log("response: ", products);
});
const [state, dispatch] = useReducer(cartReducer, {
products: products,
cart: [],
});
return <Cart.Provider value={{ state, dispatch }}>{children}</Cart.Provider>;
};
export const CartState = () => {
return useContext(Cart);
};
export default Context;
ProductService.js
import axios from "axios";
const PRODUCT_BASE_URL = "http://localhost:8080/api/v1/";
class ProductService {
getAllProducts() {
return axios.get(PRODUCT_BASE_URL + "products");
}
getProductsByCategory(category) {
return axios.get(PRODUCT_BASE_URL + "products/" + category);
}
getProductById(id) {
return axios.get(PRODUCT_BASE_URL + "product/" + id);
}
}
export default new ProductService();
Reducers.js
export const cartReducer = (state, action) => {
switch (action.type) {
default:
return state;
}
};
HomeComponenet.jsx
import React from "react";
import SlideShowComponent from "./SlideShowComponent";
import HomeCategoriesComponent from "./HomeCategoriesComponent";
import FeaturedProductsComponent from "./FeaturedProductsComponent";
import { CartState } from "../context/Context";
// class HomeComponent extends React.Component
function HomeComponent() {
const { state } = CartState();
console.log("Cart Inside the Home Component: ", state);
return (
<>
<SlideShowComponent />
<div>
<HomeCategoriesComponent />
</div>
<div>
<FeaturedProductsComponent />
</div>
</>
);
}
export default HomeComponent;

First of all, I've created a fixed example here: https://stackblitz.com/edit/react-jqtcia?file=src/Context.js
You are correct, you need to await the result from axios. In React, we use the useEffect hook for things with side effects or that should not be done as part of the render. Renders in react should be non blocking, that is they should not be dependent on things like data fetching.
A simple example of this would be if we needed it in local state. This example renders without the data, then re-renders once the data is available.
const [products, setProducts] = useState([]);
useEffect(async () => {
const { data } = await ProductService.getAllProducts();
setProducts(data);
}, []);
return <div>{products.length > 0 ? `${products.length} products` : 'Loading...'</div>
NOTE: the , []); means that this will fire once, when the first render happens.
This fixes the first part of your problem, getting the result out of the request/axios.
However, the second part and most important part is that you weren't using this value. You were attempting to insert the result as part of the initial state, but this was empty by the time it was created. As you are using reducers (useReducer), this means you need to dispatch an action for each event and handle all the relevant events to data fetching in the reducer. That means, you should need to be able to handle:
Some data is in a loading state (e.g., pagination or first load)
The data failed to load
The data is partially loaded
The data has fully loaded
I've created a minimal happy example (there is no pagination and data fetching always succeeds):
Context.js
useEffect(async () => {
const { data: loadedProducts } = await ProductService.getAllProducts();
console.log('response: ', JSON.stringify(loadedProducts));
dispatch({ type: 'PRODUCTS_LOADED', products: loadedProducts });
console.log(state);
}, []);
Reducers.js
export const cartReducer = (state, action) => {
console.log(action);
switch (action.type) {
case 'PRODUCTS_LOADED':
const newState = { ...state, products: action.products };
console.log(newState);
return newState;
default:
return state;
}
};
In fact, if you'd done this with your original code, it would've worked:
ProductService.getAllProducts().then((res) => {
dispatch({ type: 'PRODUCTS_LOADED', products : res.data});
console.log("response: ", products);
});
However, this has a different bug: It will refetch the data and then dispatch the event each time Context.js is re-rendered.
Since you've asked for more information in your comment, I'll provide it here (comments were not big enough).
I've linked the relevant API documentation for the hooks above, these provide pretty good information. React does a pretty good job of explaining the what, and why of these hooks (and the library itself). Seriously, if you haven't read their documentation, you should do so.
Additional resources:
What, when and how to use useEffect - In short, if you have something to do that isn't rendering such as data fetching, it's a side-effect and should be in a useEffect.
What is a reducer in JavaScript/React/Redux - Reducers are a pattern to make shared state easier to manage and test. The basic idea is that you define a reducer, which takes an initial state and an event/action, and produces a new state. The key idea is that there must be no side-effects, the same action and state will always produce the same result, no matter the date/time, network state, etc, etc. This makes testing and reasoning about things easier, but at the cost of a more complex state management.
However, something important that I ignored in your original question is that you are kind of reinventing the wheel here. There is already a library that will centralise your state and make it available via context, it's the library that originally invented reducers: redux. I'm guessing you have read something like this article about using context instead of redux, however the advantage of redux for you is that there is a litany of documentation about how to use it and solve these problems.
My recommendation for you is to make sure you need/want redux/reducers. It has it's value and I personally love the pattern but if you are just getting started on React, you would be better off just using useState in my opinion.

Updating Redux state and getting updated data into component with mapStateToProps ERROR

I am learning and trying to understand Redux with React
I have following test code in index.js and App.js
Where it reads API URL I make a request to API to get some data.
import React from 'react';
import ReactDOM from 'react-dom';
import { Provider } from 'react-redux'
import './index.css';
import App from './components/App';
import { createStore } from 'redux';
const initialState = {
events: [],
isViewingEvent : false,
eventIndex : 0,
eventProducts : []
}
//STORE
async function reducer(state = initialState, action) {
switch(action.type) {
case "GETEVENTS":
{
const response = await fetch("API URL", {
method: 'get',
headers: {'Content-Type':'application/json','Accept': 'application/json'}
})
.then(function(response) {
return response.json();
})
console.log(response);
return state.events = response;
};
default:
return state;
}
}
const store = createStore(reducer);
ReactDOM.render(
<Provider store={store}>
<App />
</Provider>,
document.getElementById('root')
)
Now App.js
import { Component } from 'react';
import { connect } from 'react-redux'
class App extends Component {
handleOnClick() {
this.props.dispatch({ type : "GETEVENTS" })
}
render() {
return <div>
<header>
<button onClick={() => this.handleOnClick()}>TEST</button>
</header>
</div>
}
}
const mapStateToProps = (state) => {
console.log(state.events);
return {
events: state.events
}
}
export default connect(mapStateToProps)(App);
I simply wish to test if I can update state with Clicking a button, by calling the dispatch function.
dispatch function makes a API get request and should update state with its response.
I have console.log output in dispatch function to see what the response is, and it will show it correctly. I will get valid data from API.
Another console.log is at mapStateToProps function in App.js, where I'd like to get that events data as a prop from state. This will always show me undefined when I click the button. I can see I get valid response from API but I can never get that data as prop into App.js
What am I doing wrong here? I can think of that mapStateToProps happens before I get async response from API. So its mapping props before state update? But then if I click it the second time I should see data. But I dont, so Im missing something here which I do not understand.
this is my console.log output

You are doing an API request in the reducer here, which is not only conceptually something you should not do in a reducer (side effects are not allowed to happen there), but in this case also something that is just plain impossible, because it turns the whole state slice into a promise.
You need to handle API requests & co outside the reducer in a middleware, for example a thunk. I recommend looking into the Async Logic and Data Fetching chapter of the official redux tutorial.

You are changing the state in your reducer function directly which is the wrong way to do it as it is immutable. Read about it here: Immutable patterns redux
async function reducer(state = initialState, action) {
...
console.log(response);
return state.events = response; // here is the problem
};
...
}
Try one of the suggested approaches on the link provided.

react-admin: dispatch action to store meta data from dynamic request

Hi this question is a continue to this one!
I'm getting my routes dynamically via an ajax request (following this article in the official docs "Declaring resources at runtime"), I'm using an async function to return a list of resources from an ajax request.
What is the best way to dispatch an action to store meta data, which I got form ajax request in redux, for later access?
Also when user has not yet logged in, this function will not return anything, after logging in, user will have access to a couple of resources. What is the best way to reload resources?

The best option is to use redux-saga. https://redux-saga.js.org/docs/introduction/BeginnerTutorial.html
Then
export function* async() {
yield fetch(); //your Ajax call function
yield put({ type: 'INCREMENT' }) //call your action to update your app
}
Incase you can't use redux-saga, I like your solution with private variable. You should go ahead with that.

To get this to work, I added a private variable, which I store the data mentioned in the question, and I access it via another function, which I exported from that file.
This gives me what I need, but I don't know if it's the best way to go.

https://github.com/redux-utilities/redux-actions
redux-actions is really simple to setup. Configure the store and then you can setup each state value in a single file:
import { createAction, handleActions } from 'redux-actions'
let initialState = { myValue: '' }
export default handleActions({
SET_MY_VALUE: (state, action) => ({...state, myValue: action.payload})
})
export const setMyValue = createAction('SET_MY_VALUE')
export const doSomething = () => {
return dispatch => {
doFetch().then(result => {
if (result.ok) dispatch(setMyValue(result.data))
})
}
}
Then in your component you just connect and you can access the state value
import React from 'react'
import PropTypes from 'prop-types'
import { connect } from 'react-redux'
class MyComponent extends React.Component {
render = () => (
<span>{this.props.myValue}</span>
)
}
MyComponent.propTypes = {
myValue: PropTypes.string.isRequired
}
const mapStateToProps = (state) => ({
myValue: state.myState.myValue
})
const mapDispatchToProps = () => ({})
export default connect(mapStateToProps, mapDispatchToProps)(MyComponent)

ReactJs Redux Data Fetch

I just started to work on React Js and Redux-Thunk. Currently, I am trying to fetch data from a url using redux-thunk. I got data successfully but the issue is that it renders undefined data twice, then it gives me the desired data in props.
Here is my code.
In Actions
index.js
function getData() {
return {
type: 'FETCH'
}
}
function getSuccess(data) {
return {
type: 'FETCH_SUCCESS',
payload: data
}
}
function getFailed(err) {
return {
type: 'FAILED',
payload: err
}
}
export function fetchData() {
const thunk = async function thunk(dispatch) {
try {
dispatch(getData());
const body = await fetch("http://jsonplaceholder.typicode.com/users")
const res = await body.json();
console.log("Thunk", res);
dispatch(getSuccess(res));
}
catch(err) {
dispatch(getFailed(err));
}
}
return thunk;
}
In Reducers fetch.js
const initialState = {
state: []
}
export default function(state=initialState , actions) {
switch(actions.type) {
case 'FETCH':
return {
...state
}
case 'FETCH_SUCCESS':
return {
...state,
data: actions.payload
}
case 'FAILED':
return {
...state
}
default:
return state;
}
}
Reducers Index.js
import fetch from './fetch';
import { combineReducers } from 'redux';
const rootReducer = combineReducers ({
fetch
});
export default rootReducer;
App.js
import React, { Component } from 'react';
import './App.css';
import Main from './component/Main';
import { createStore, applyMiddleware } from 'redux';
import rootReducer from './reducers';
import thunk from 'redux-thunk';
import { Provider } from 'react-redux';
const store = createStore(
rootReducer,
applyMiddleware(thunk)
);
console.log("STore", store.getState());
class App extends Component {
render() {
return (
<Provider store={store}>
<Main/>
</Provider>
);
}
}
export default App;
Main.jsx
import React, { Component } from 'react';
import { connect } from 'react-redux';
import * as actions from '../actions';
class Main extends Component {
componentWillMount() {
const { fetchData } = this.props
fetchData();
}
render() {
let mydata = this.props.data.data;
console.log("Data .....<>", mydata);
return(
<div>
Main
</div>
);
}
}
const mapStateToProps =(state)=> {
return {
data: state.fetch
}
}
export default connect(mapStateToProps, {fetchData: actions.fetchData})(Main);
Output Screen Shot
Please let me know what i am doing wrong. Any help will be appreciated.
Thanks

This behavior is correct. You're doing everything in the normal way, except calling async operations in componentWillMount method instead of componentDidMount.
Read more here about it.
You need to know, that when you are using componentDidMount - you are handle this in a safe way due to commit phase in component lifecycle and it means that your request will be guaranteed trigger once instead of possible several times, which can be in render phase.
See here the visual diagram to understand this more.
Regarding several renderings - it can be explained easily.
First time, when your component is mounting you are calling asynchronous operation and it needs more time to load data than for component mounting. Thats why you are accessing data property of your initialState (which is empty array), and getting undefined.
When you response is ready and actions is being dispatched, redux trigger re-render of connected components with new state.
If you want to make your async-await syntax works you should make lifecycle with async keyword as well and await your request inside.
NOTE: It's safe, but in several cases it might cause unexpected bugs, so keep in mind. Nevertheless, I don't recommend to use it in a such way. Read about this topic in the another thread at SO.
I advice you to create some isLoading boolean status in your reducer and keep track whether data is loaded or not.
Good luck! Hope it will helps!

There is nothing wrong with your code, but there is one unnecessary action.
Why do you see two times undefined and then you see your data?
First one is coming from the initial render. You are making an async dispatching in your componentWillMount so render does not wait for it, then try to log your data. At that time it is undefined.
Your fetchData dispatches two actions: getData and getSuccess. You see second undefined because of getData action since it returns current state which props.data.data undefined at that time again.
You see the data since getSuccess updates your state now.
If you want to test this comment out getData in your fetchData function, just use getSuccess and change your console.log in the render like that:
mydata && console.log("Data .....<>", mydata);
I think getData action is unnecessary here, it does not do anything beside returning the current state. Also, try to use componentDidMount instead of componentWillMount since it will be deprecated in version 17.

Async with redux works? But still gives error, should I ignore it?

I am using a mix of laravel, react.
Attempting to implement the redux-thunk middleware.
I am having issues with async calls.
I would like to use jquery for ajax (which successfully retrieve the API data, but I am getting an error which reads,
"Error: dispatch is not a function", meaning I cannot make any changes to the store. From what I understand dispatch and GetState is passed through the thunk middle-ware. Correct?So why am I not able to use the function?
It also gives me an error which reads: "Error: Actions may not have an undefined "type" property. Have you misspelled a constant?"
Another issue that arises, after trying to deal with the above issue is: "Error: Actions must be plain objects. Use custom middleware for async actions."
I have read many similar questions but I still cannot seem to get it to work.
"Actions must be plain objects. Use custom middleware for async actions."
index.js
import React from 'react';
import ReactDOM from 'react-dom';
import { Provider } from 'react-redux'
import FilterBar from './SideBar/FilterBar';
import Store from '../redux/store/mainStore';
import { REMOVE_ATTRIBUTE_FILTER,ADD_ATTRIBUTE_TO_FILTER, removeAttribute } from '../redux/actions/actions';
Store.subscribe(()=>{
console.log("store changes", Store.getState())
})
console.log(Store.getState());
Store.dispatch({
type:ADD_ATTRIBUTE_TO_FILTER,
payload:{'make':23}
})
if (document.getElementById('InventoryDisplay')) {
ReactDOM.render(
<Provider store={Store}>
<FilterBar/>
</Provider>
,document.getElementById('FilterBar'));
}
mainstore.js
```
import { createStore,applyMiddleware,combineReducers,compose } from 'redux';
import thunk from 'redux-thunk';
import {inventoryFilter,availableAttributes} from '../reducers/reducer';
const Store = createStore(
///combine imported reducers
combineReducers({
activeFilter:inventoryFilter,
availableAttributes:availableAttributes
},
///initilize store
{},
applyMiddleware(thunk)
));
export default Store;
```
actions.js what is relevant
```
///first case
const getAttributes2 = (dispatch) => {
return(
$.ajax('/getFilteredAttributes/', {
type: 'GET',
dataType : 'json'
}).done(response => {
dispatch(addAttribute("make",32));
}).fail((xhr, status, error) => {
console.log("failed");
})
)
};
///second case
const getAttributes = (dispatch) => {
return ()=>{}
}
export {
ADD_ATTRIBUTE_TO_FILTER,addAttribute,
REMOVE_ATTRIBUTE_FILTER,removeAttribute,
GET_INVENTORY,getInventory,
GET_AVAILABLE_ATTRIBUTES,getAttributes,
}
```
component connect to store that dispatch action
```
import React from 'react';
import {bindActionCreators} from 'redux';
import {connect} from 'react-redux';
import PropTypes from 'prop-types';
import * as ActionCreators from '../../../redux/actions/actions';
class DropDownList extends React.Component{
componentDidMount(){
this.props.addAttributes("make",32)
this.props.getAttributes()
this.props.removeAttributes("make",32)
}
render(){
return(
<div>
</div>
)
}
}
function mapStatesToProps(state){
return{
activeFilters:state.activeFilter,
availableAttributes:state.availableAttributes
}
};
const mapDispatchToProps = dispatch => {
return {
addAttributes: (type,value) => {
dispatch(ActionCreators.addAttribute(type,value))
},
removeAttributes: (type,value) => {
dispatch(ActionCreators.removeAttribute(type,value))
},
getAttributes: () => {
dispatch(ActionCreators.getAttributes())
}
}
}
DropDownList.propTypes = {
availableAttributes: PropTypes.object.isRequired,
activeFilters: PropTypes.object.isRequired,
}
export default connect(mapStatesToProps,mapDispatchToProps)(DropDownList)
```
My solution for case one for the second error was to just place the ajax function call into in object that contains the "type" property. Like such
return (
{
type: "Something",
$.ajax('/getFilteredAttributes/', {
type: 'GET',
dataType: 'json'
}).done(response => {
dispatch(addAttribute("make", 32));
}).fail((xhr, status, error) => {
console.log("failed");
})
})
The ajax call is made, but dispatch still isn't available, I am lost and looking for the best solution? Maybe I am overthinking something or missed a minor detail. I have tried other solutions but none has worked for me.
Please Help.

It's pretty difficult to know exactly what's going on, but I definitely wouldn't recommend ignoring / hacking round an error you're getting using a common feature of a popular library. It's important to get your implementation right for simplicity moving forward.
It looks to me like the way you are using thunk is a little odd.
The function that is returned by the action you dispatch has dispatch and getState as arguments:
In your case your thunk action might look like this
In your actions.js:
export function getAttributes2(){
return function(dispatch, getState){
// you could dispatch a fetching action here before requesting!
return $.ajax('/getFilteredAttributes/', {type: 'GET', dataType: 'json'})
.done(response => dispatch(saveTheResponseAction(response)))
.fail((xhr, status, error) => console.log("failed"))
}
Mapping that thunk function to your props:
import {getAttributes2} from '../../../redux/actions/actions';
const mapDispatchToProps = dispatch => {
return {
getAttributes2: () => dispatch(getAttributes2()),
}
}
This way you can dispatch an action from the .done part of your api call with the result in it, you can respond to errors, you can even dispatch an action before returning your api call to let redux know you've requested but not yet received the data, allowing you to do all kinds of loading states.
I hope this helps, let me know :)