We Keep Coding

Why does the UI not update for async/await function

This is my first website created with JavaScript. I'm trying to get items from API and then display them for the user.
My function:
getOrderItem = async (itemId: string) => {
console.log(await api.getItem(itemId))
return await api.getItem(itemId)
}
This is how I'm calling it in my UI:
<h4>Quantity: {item.quantity} Name: {this.getOrderItem(item.id).name}</h4>
My UI does not update but I can see that the function is working:
What I'm doing wrong with await/async?

try using the setState() hook with the useEffect() hook so you can tell React to re-render the DOM elements once your getOrderItem fulfills.
You can try setting it up like this:
const [getOrderItem, setOrderItem] = useState({})
getOrderItem = async (itemId: string) => {
console.log(await api.getItem(itemId))
return await api.getItem(itemId)
}
useEffect(() => {
setOrderItem(getOrderItem())
}, [])
return (
<h4>Quantity: {item.quantity} Name: {getOrderItem.name}</h4>
)

your function doesn't return anything until you get your response from the API. And by the time you get your response the UI is rendered already. Since the function doesn't update any state variables your UI doesn't re-render. You should use a state variable to store the response of the API.
getOrderItem = async (itemId: string) => {
let response = await api.getItem(itemId);
this.setState({items: {...this.state.items, itemId: response}});
}
Now, you can use the state variable to re-render
<h4>Quantity: {item.quantity} Name: {item.id in this.state.items ? this.state.items[item.id].name ? this.getOrderItem(item.id) }</h4>
If you only need the names of the items, you can store response.name instead of response

React: String automatically converted to [object promise] when called from another component

I'm developing the front-end for my spring boot application. I set up an initial call wrapped in a useEffect() React.js function:
useEffect(() => {
const getData = async () => {
try {
const { data } = await fetchContext.authAxios.get(
'/myapi/' + auth.authState.id
);
setData(data);
} catch (err) {
console.log(err);
}
};
getData();
}, [fetchContext]);
The data returned isn't comprehensive, and needs further call to retrieve other piece of information, for example this initial call return an employee id, but if I want to retrieve his name and display it I need a sub-sequential call, and here I'm experiencing tons of issues:
const getEmployeeName = async id => {
try {
const name = await fetchContext.authAxios.get(
'/employeeName/' + id
);
console.log((name["data"])); // <= Correctly display the name
return name["data"]; // return an [Object promise],
} catch (err) {
console.log(err);
}
};
I tried to wrap the return call inside a Promise.resolve() function, but didn't solve the problem. Upon reading to similar questions here on stackoverflow, most of the answers suggested to create a callback function or use the await keyword (as I've done), but unfortunately didn't solve the issue. I admit that this may not be the most elegant way to do it, as I'm still learning JS/React I'm open to suggestions on how to improve the api calls.
var output = Object.values(data).map((index) =>
<Appointment
key={index["storeID"].toString()}
// other irrelevant props
employee={name}
approved={index["approved"]}
/>);
return output;

Async functions always return promises. Any code that needs to interact with the value needs to either call .then on the promise, or be in an async function and await the promise.
In your case, you should just need to move your code into the existing useEffect, and setState when you're done. I'm assuming that the employeeID is part of the data returned by the first fetch:
const [name, setName] = useState('');
useEffect(() => {
const getData = async () => {
try {
const { data } = await fetchContext.authAxios.get(
"/myapi/" + auth.authState.id
);
setData(data);
const name = await fetchContext.authAxios.get(
'/employeeName/' + data.employeeID
);
setName(name.data);
} catch (err) {
console.log(err);
}
};
getData();
}, [fetchContext]);
// ...
var output = Object.values(appointmentsData).map((index) =>
<Appointment
key={index["storeID"].toString()}
// other irrelevant props
employee={name}
approved={index["approved"]}
/>);
return output;
Note that the above code will do a rerender once it has the data (but no name), and another later when you have the name. If you want to wait until both fetches are complete, simply move the setData(data) down next to the setName

How to use an async database call to set a variable with useState() and useEffect()?

I'm trying to set a variable with a simple GET database call. The database call is returning the data correctly, but the variable remains undefined after every re-render. Code is below... the getMyThing() function in the useState() function is working correctly and returning the data I want.
import { getMyThing } from '../../utils/databaseCalls'
const MyComponent: React.FC = () => {
const { id } = useParams();
const [myThing, setMyThing] = useState(getMyThing(id));
useEffect(() => {
setMyThing(myThing)
}, [myThing]);
}
My thinking here was to use useState() to set the initial state of the myThing variable with the data returned from my database. I assume it's not immediately working since a database call is asynchronous, so I thought I could use useEffect() to update the myThing variable after the response of the database call completes, since that would trigger the useEffect() function because I have the myThing variable included as a dependency.
What am I missing here? Thanks!
EDIT: Thanks for the answers everyone, but I still can't get it to work by calling the getMyThing function asynchronously inside useEffect(). Is something wrong with my database call function? I guess it's not set up to a return a promise? Here's what that looks like:
export const getMyThing = (id) => {
axios.get('http://localhost:4000/thing/' + id)
.then(response => {
return(response.data);
})
.catch(function (error){
console.log(error);
})
}

You should do all your side effects(fetching data, subscriptions and such) in useEffect hooks and event handlers. Don't execute async logic in useState as you just assign the promise itself to the variable and not the result of it. In any case, it is a bad practice and it won't work. You should either:
import { getMyThing } from '../../utils/databaseCalls'
const MyComponent: React.FC = () => {
const { id } = useParams();
const [myThing, setMyThing] = useState(null);
useEffect(() => {
const fetchData = async () => {
const result = await getMyThing(id);
setMyThing(result);
};
fetchData();
}, [id, getMyThing]);
}
Or if you don't want to introduce an async function:
import { getMyThing } from '../../utils/databaseCalls'
const MyComponent: React.FC = () => {
const { id } = useParams();
const [myThing, setMyThing] = useState(null);
useEffect(() => {
getMyThing()
.then(result => setMyThing(result));
}, [id, getMyThing]);
}
Also, take note of the [id, getMyThing] part as it is important. This is a dependency array determining when your useEffect hooks are gonna execute/re-execute.

If getMyThing returns a Promise, the myThing will be set to that Promise on the first render, and then myThing will stay referring to that Promise. setMyThing(myThing) just sets the state to the Promise again - it's superfluous.
Call the asynchronous method inside the effect hook instead:
const [myThing, setMyThing] = useState();
useEffect(() => {
getMyThing(id)
.then(setMyThing);
}, []);
Here, myThing will start out undefined, and will be then set to the result of the async call as soon as it resolves.

You can't set the initial state with a value obtained asynchronously because you can't have the value in time.
myThing cannot both return the value you want and be asynchronous. Maybe it returns a promise that resolves to what you want.
Set an initial value with some default data. This might be null data (and later when you return some JSX from your component you can special case myThing === null by, for example, returning a Loading message).
const [myThing, setMyThing] = useState(null);
Trigger the asynchronous call in useEffect, much like you are doing now, but:
Make it rerun when the data it depends on changes, not when the data it sets changes.
Deal with whatever asynchronous mechanism your code uses. In this example I'll assume it returns a promise.
Thus:
useEffect(async () => {
const myNewThing = await getMyThing(id);
setMyThing(myNewThing)
}, [id]);

Function inside component not receiving latest version of Redux-state to quit polling

I have an issue where I am trying to use the Redux state to halt the execution of some polling by using the state in an if conditional. I have gone through posts of SO and blogs but none deal with my issue, unfortunately. I have checked that I am using mapStateToProps correctly, I update state immutably, and I am using Redux-Thunk for async actions. Some posts I have looked at are:
Component not receiving new props
React componentDidUpdate not receiving latest props
Redux store updates successfully, but component's mapStateToProps receiving old state
I was kindly helped with the polling methodology in this post:Incorporating async actions, promise.then() and recursive setTimeout whilst avoiding "deferred antipattern" but I wanted to use the redux-state as a single source of truth, but perhaps this is not possible in my use-case.
I have trimmed down the code for readability of the actual issue to only include relevant aspects as I have a large amount of code. I am happy to post it all but wanted to keep the question as lean as possible.
Loader.js
import { connect } from 'react-redux';
import { delay } from '../../shared/utility'
import * as actions from '../../store/actions/index';
const Loader = (props) => {
const pollDatabase = (jobId, pollFunction) => {
return delay(5000)
.then(pollFunction(jobId))
.catch(err => console.log("Failed in pollDatabase function. Error: ", err))
};
const pollUntilComplete = (jobId, pollFunction) => {
return pollDatabase(jobId, pollFunction)
.then(res => {
console.log(props.loadJobCompletionStatus) // <- always null
if (!props.loadJobCompletionStatus) { <-- This is always null which is the initial state in reducer
return pollUntilComplete(jobId, pollFunction);
}
})
.catch(err=>console.log("Failed in pollUntilComplete. Error: ", err));
};
const uploadHandler = () => {
...
const transferPromise = apiCall1() // Names changed to reduce code
.then(res=> {
return axios.post(api2url, res.data.id);
})
.then(postResponse=> {
return axios.put(api3url, file)
.then(()=>{
return instance.post(api3url, postResponse.data)
})
})
transferDataPromise.then((res) => {
return pollUntilComplete(res.data.job_id,
props.checkLoadTaskStatus)
})
.then(res => console.log("Task complete: ", res))
.catch(err => console.log("An error occurred: ", err))
}
return ( ...); //
const mapStateToProps = state => {
return {
datasets: state.datasets,
loadJobCompletionStatus: state.loadJobCompletionStatus,
loadJobErrorStatus: state.loadJobErrorStatus,
loadJobIsPolling: state.loadJobPollingFirestore
}
}
const mapDispatchToProps = dispatch => {
return {
checkLoadTaskStatus: (jobId) =>
dispatch(actions.loadTaskStatusInit(jobId))
};
};
export default connect(mapStateToProps, mapDispatchToProps)(DataLoader);
delay.js
export const delay = (millis) => {
return new Promise((resolve) => setTimeout(resolve, millis));
}
actions.js
...
export const loadTaskStatusInit = (jobId) => {
return dispatch => {
dispatch(loadTaskStatusStart()); //
const docRef = firestore.collection('coll').doc(jobId)
return docRef.get()
.then(jobData=>{
const completionStatus = jobData.data().complete;
const errorStatus = jobData.data().error;
dispatch(loadTaskStatusSuccess(completionStatus, errorStatus))
},
error => {
dispatch(loadTaskStatusFail(error));
})
};
}
It seems that when I console log the value of props.loadJobCompletionStatus is always null, which is the initial state of in my reducer. Using Redux-dev tools I see that the state does indeed update and all actions take place as I expected.
I initially had placed the props.loadJobCompletionStatus as an argument to pollDatabase and thought I had perhaps created a closure, and so I removed the arguments in the function definition so that the function would fetch the results from the "upper" levels of scope, hoping it would fetch the latest Redux state. I am unsure as to why I am left with a stale version of the state. This causes my if statement to always execute and thus I have infinite polling of the database.
Can anybody point out what might be causing this?
Thanks

I'm pretty sure this is because you are defining a closure in a function component, and thus the closure is capturing a reference to the existing props at the time the closure was defined. See Dan Abramov's extensive post "The Complete Guide to useEffect" to better understand how closures and function components relate to each other.
As alternatives, you could move the polling logic out of the component and execute it in a thunk (where it has access to getState()), or use the useRef() hook to have a mutable value that could be accessed over time (and potentially use a useEffect() to store the latest props value in that ref after each re-render). There are probably existing hooks available that would do something similar to that useRef() approach as well.

React and jest mock module

I am creating an application in which I use redux and node-fetch for remote data fetching.
I want to test the fact that I am well calling the fetch function with a good parameter.
This way, I am using jest.mock and jasmine.createSpy methods :
it('should have called the fetch method with URL constant', () => {
const spy = jasmine.createSpy('nodeFetch');
spy.and.callFake(() => new Promise(resolve => resolve('null')));
const mock = jest.mock('node-fetch', spy);
const slug = 'slug';
actionHandler[FETCH_REMOTE](slug);
expect(spy).toHaveBeenCalledWith(Constants.URL + slug);
});
Here's the function that I m trying to test :
[FETCH_REMOTE]: slug => {
return async dispatch => {
dispatch(loading());
console.log(fetch()); // Displays the default fetch promise result
await fetch(Constants.URL + slug);
addLocal();
};
}
AS you can see, I am trying to log the console.log(fetch()) behavior, and I am having the default promise to resolve given by node-fetch, and not the that I've mock with Jest and spied with jasmine.
Do you have an idea what it doesn't work ?
EDIT : My test displayed me an error like my spy has never been called

Your action-handler is actually a action handler factory. In actionHandler[FETCH_REMOTE], you are creating a new function. The returned function taskes dispatch as a parameter and invokes the code you are showing.
This means that your test code will never call any function on the spy, as the created function is never invoked.
I think you will need to create a mock dispatch function and do something like this:
let dispatchMock = jest.fn(); // create a mock function
actionHandler[FETCH_REMOTE](slug)(dispatchMock);
EDIT:
To me, your actionHandler looks more like an actionCreator, as it is usually called in redux terms, though I personally prefer to call them actionFactories because that is what they are: Factories that create actions.
As you are using thunks(?) your actionCreater (which is misleadingly named actionHandler) does not directly create an action but another function which is invoked as soon as the action is dispatched. For comparison, a regular actionCreator looks like this:
updateFilter: (filter) => ({type: actionNames.UPDATE_FILTER, payload: {filter: filter}}),
A actionHandler on the other hand reacts to actions being dispatched and evaluates their payload.
Here is what I would do in your case:
Create a new object called actionFactories like this:
const actionFactories = {
fetchRemote(slug): (slug) => {
return async dispatch => {
dispatch(loading());
console.log(fetch()); // Displays the default fetch promise result
let response = await fetch(Constants.URL + slug);
var responseAction;
if (/* determine success of response */) {
responseAction = actionFactories.fetchSuccessful(response);
} else {
responseAction = actionFactories.fetchFailed();
}
dispatch(responseAction);
};
}
fetchFailed(): () => ({type: FETCH_FAILED, }),
fetchSuccessful(response): () => ({type: FETCH_FAILED, payload: response })
};
Create an actionHandler for FETCH_FAILED and FETCH_SUCCESSFUL to update the store based on the response.
BTW: Your console.log statement does not make much sense too me, since fetch just returns a promise.