React State update asynchronous issue - reactjs

I have this component which creates row data for a table. It sets state. It also creates a button for one of the row states, which contains a reference to a function. I want the state to be available to that button. But it is one request behind. The state available in the showJourneyDetails function is always the previous state to the current state. I know react state is asynchronous so how do I make the current state available inside the showJourneyDetails function?
const [suspected, setSuspectedData] = useState([]);
const [suspectedReads, setSuspectedReads] = useState(false);
const findVehiclesOfInterestBetweenDateRange = () => {
fetch(`http://127.0.0.1:8000/vehicles`)
.then((response) => response.json())
.then((vehicles) => {
const suspectedDataReads = vehicles.map((row) => {
return {
journey_id: row.journey_id,
reads: row.reads,
};
});
setSuspectedReads(suspectedDataReads);
const suspected = vehicles.map((row) => {
return {
vrm: row.vrm,
start_time: row.start_time,
end_time: row.end_time,
journey_size: row.journey_size,
journey_time: row.journey_time,
score: row.score,
details: (<Button
variant="contained"
onClick={showJourneyDetails}
id={row.journey_id}
>
Details
</Button>),
};
});
setSuspectedData(suspected);
})
.catch((error) => {
console.log(error);
});
};
const showJourneyDetails = (event) => {
console.log(event.target.id);
console.log("showJourneyDetails suspectedDataReads:", suspectedDataReads);
}

Related

Cannot setstate in nested axios post request in react

I am trying to access the res.data.id from a nested axios.post call and assign it to 'activeId' variable. I am calling the handleSaveAll() function on a button Click event. When the button is clicked, When I console the 'res.data.Id', its returning the value properly, but when I console the 'activeId', it's returning null, which means the 'res.data.id' cannot be assigned. Does anyone have a solution? Thanks in advance
const [activeId, setActiveId] = useState(null);
useEffect(() => {}, [activeId]);
const save1 = () => {
axios.get(api1, getDefaultHeaders())
.then(() => {
const data = {item1: item1,};
axios.post(api2, data, getDefaultHeaders()).then((res) => {
setActiveId(res.data.id);
console.log(res.data.id); // result: e.g. 10
});
});
};
const save2 = () => {
console.log(activeId); // result: null
};
const handleSaveAll = () => {
save1();
save2();
console.log(activeId); // result: again its still null
};
return (
<button type='submit' onClick={handleSaveAll}>Save</button>
);
Setting the state in React acts like an async function.
Meaning that the when you set the state and put a console.log right after it, like in your example, the console.log function runs before the state has actually finished updating.
Which is why we have useEffect, a built-in React hook that activates a callback when one of it's dependencies have changed.
Example:
useEffect(() => {
console.log(activeId);
}, [activeId);
The callback will run every time the state value changes and only after it has finished changing and a render has occurred.
Edit:
Based on the discussion in the comments.
const handleSaveSections = () => {
// ... Your logic with the `setState` at the end.
}
useEffect(() => {
if (activeId === null) {
return;
}
save2(); // ( or any other function / logic you need )
}, [activeId]);
return (
<button onClick={handleSaveSections}>Click me!</button>
)
As the setState is a async task, you will not see the changes directly.
If you want to see the changes after the axios call, you can use the following code :
axios.post(api2, data, getDefaultHeaders())
.then((res) => {
setActiveId(res.data.id)
console.log(res.data.id) // result: e.g. 10
setTimeout(()=>console.log(activeId),0);
})
useEffect(() => {
}, [activeId]);
const [activeId, setActiveId] = useState(null);
const save1 = () => {
const handleSaveSections = async () => {
activeMetric &&
axios.get(api1, getDefaultHeaders()).then(res => {
if (res.data.length > 0) {
Swal.fire({
text: 'Record already exists',
icon: 'error',
});
return false;
}
else {
const data = {
item1: item1,
item2: item2
}
axios.post(api2, data, getDefaultHeaders())
.then((res) => {
setActiveId(res.data.id)
console.log(res.data.id) // result: e.g. 10
})
}
});
}
handleSaveSections()
}
const save2 = () => {
console.log(activeId); //correct result would be shown here
}
const handleSaveAll = () => {
save1();
save2();
}
return (
<button type="submit" onClick={handleSaveAll}>Save</button>
)

Race condition when combining async action and accessing local state

Suppose I have a list of items I would like to render and select (like a Todo app).
I'd like to keep the selection logic inside custom react hook and have items live somewhere else in local state.
Now, I would like to update the selection list, kept in the custom hook, whenever I fetch some more items. For this task I am passing data as parameter to selection hook and I am using useEffect to update the selection:
import { useEffect, useState } from "react";
const itemsArrayToObject = (items) =>
Object.fromEntries(items.map((i) => [i.id, { ...i, selected: false }]));
export function useSelection({ data }) {
const [selection, setSelection] = useState(itemsArrayToObject(data));
useEffect(() => {
setSelection((selection) => {
return {
...itemsArrayToObject(data),
...selection
};
});
}, [data]);
const isSelected = (itemId) => selection?.[itemId]?.selected ?? false;
const toggle = (itemId) => {
setSelection((s) => {
const item = s[itemId];
return {
...s,
[itemId]: {
...item,
selected: !item.selected
}
};
});
};
return {
isSelected,
toggle
};
}
This almost works but the problem is if I want to synchronize two things: fetching data and toggling items. Eg.
const onLoadAndToggle = async () => {
await load();
toggle(0);
};
load is a async function that fetches the data. It also triggers state update so that data is updated and the selection can be updated inside useSelection hook.
Example how it all can work:
const [data, setData] = useState([]);
const addItems = (items) => {
setData((state) => [...state, ...items]);
};
const { load } = useFetch({ addItems });
const { isSelected, toggle } = useSelection({ data });
const onLoadAndToggle = async () => {
await load();
toggle(0);
};
Now, the problem is that when calling toggle(0) my custom hook has a stale selection, even when using setState(state => ... singature.
It is because the whole fetching and updating data in state takes too long.
I can see some ugly ways to solve that problem but I wonder what would be the elegant or idiomatic react way to solve that.
I have made a code sandbox, if it helps: https://codesandbox.io/s/selection-fetch-forked-nyl0kt?file=/src/App.js:376-512
Try clicking "Load and toggle first" first to see how the app crashed because the selection is not yet updated.
What you need is to initialize toogled items from the code itself. We can do this by providing the id's of the items that we want to toggle to the hook itself.
Updated hook -
const itemsArrayToObject = (items, itemsToggled) => {
if (Array.isArray(itemsToggled)) {
return Object.fromEntries(
items.map((i) => [i.id, { ...i, selected: itemsToggled.includes(i.id) }])
);
}
return Object.fromEntries(
items.map((i) => [i.id, { ...i, selected: false }])
);
};
export function useSelection({ data }, itemsToggled) {
const [selection, setSelection] = useState(
itemsArrayToObject(data, itemsToggled)
);
useEffect(() => {
setSelection((selection) => {
return {
...itemsArrayToObject(data, itemsToggled),
...selection
};
});
}, [data, itemsToggled]);
Now call to hook becomes -
const { isSelected, toggle } = useSelection({ data }, [0, 1]);
Updated codesandbox
This also decouples loading data & toggling of an item initially.

useEffect function inside context unaware of state changes inside itself

I am building a messaging feature using socket.io and react context;
I created a context to hold the conversations that are initially loaded from the server as the user passes authentication.
export const ConversationsContext = createContext();
export const ConversationsContextProvider = ({ children }) => {
const { user } = useUser();
const [conversations, setConversations] = useState([]);
const { socket } = useContext(MessagesSocketContext);
useEffect(() => {
console.log(conversations);
}, [conversations]);
useEffect(() => {
if (!socket) return;
socket.on("userConversations", (uc) => {
let ucc = uc.map((c) => ({
...c,
participant: c.participants.filter((p) => p._id != user._id)[0],
}));
setConversations([...ucc]);
});
socket.on("receive-message", (message) => {
console.log([...conversations]);
console.log(message);
setConversations((convs) => {
let convIndex = convs.findIndex(
(c) => c._id === message.conversation._id
);
let conv = convs[convIndex];
convs.splice(convIndex, 1);
conv.messages.unshift(message);
return [conv, ...convs];
});
});
}, [socket]);
return (
<ConversationsContext.Provider
value={{
conversations,
setConversations,
}}
>
{children}
</ConversationsContext.Provider>
);
};
The conversations state is updated with the values that come from the server, and I have confirmed that on the first render, the values are indeed there.
Whenever i am geting a message, when the socket.on("receive-message", ...) function is called, the conversations state always return as []. When checking devTools if that is the case I see the values present, meaning the the socket.on is not updated with the conversations state.
I would appreciate any advice on this as I`m dealing with this for the past 3 days.
Thanks.
You can take "receive-message" function outside of the useEffect hook and use thr reference as so:
const onReceiveMessageRef = useRef();
onReceiveMessageRef.current = (message) => {
console.log([...conversations]);
console.log(message);
setConversations((convs) => {
let convIndex = convs.findIndex(
(c) => c._id === message.conversation._id
);
let conv = convs[convIndex];
convs.splice(convIndex, 1);
conv.messages.unshift(message);
return [conv, ...convs];
});
};
useEffect(() => {
if (!socket) return;
socket.on("userConversations", (uc) => {
let ucc = uc.map((c) => ({
...c,
participant: c.participants.filter((p) => p._id != user._id)[0],
}));
setConversations([...ucc]);
});
socket.on("receive-message", (...r) => onReceiveMessageRef.current(...r));
}, [socket]);
let me know if this solves your problem

React function updates state on second onClick?

I'm working on a hotel feature where the user can filter through and display the corresponding rooms available, however when I set the onClick to update the filters and display the filtered rooms, the rooms display correctly after the second click and there after.
const toggleSelection = (e) => {
setFilters((prevFilters) => ({
...prevFilters,
[e.name]: e.id,
}));
filterRooms();
};
const filterRooms = () => {
....
....
setRooms((prevRooms) => ({
...prevRooms,
filtered: filtered_rooms,
}));
};
useState() (and class component's this.setState()) are asynchronous, so your second state updater won't have an up to date value for filtered_rooms when it runs.
Rather than:
const [some_state, setSomeState] = useState(...);
const [some_other_state, setSomeOtherState] = useState(...);
const someHandler = e => {
setSomeState(...);
setSomeOtherState(() => {
// Uses `some_state` to calculate `some_other_state`'s value
});
};
You need to setSomeOtherState within a useEffect hook, and ensure to mark some_state as a dependency.
const [some_state, setSomeState] = useState(...);
const [some_other_state, setSomeOtherState] = useState(...);
useEffect(() => {
setSomeOtherState(() => {
// Uses `some_state` to calculate `some_other_state`'s value
});
}, [some_state]);
const someHandler = e => {
setSomeState(...);
};
It is hard to give an suggestion for your code since it is fairly edited, but it'd probably look like this:
const filterRooms = () => {
// ...
setRooms((prevRooms) => ({
...prevRooms,
filtered: filtered_rooms,
}));
};
useEffect(() => {
filterRooms();
}, [filtered_rooms]);
const toggleSelection = (e) => {
setFilters((prevFilters) => ({
...prevFilters,
[e.name]: e.id,
}));
};
See this codepen for a simple (albeit a bit contrived) example.

React hooks : how to watch changes in a JS class object?

I'm quite new to React and I don't always understand when I have to use hooks and when I don't need them.
What I understand is that you can get/set a state by using
const [myState, setMyState] = React.useState(myStateValue);
So. My component runs some functions based on the url prop :
const playlist = new PlaylistObj();
React.useEffect(() => {
playlist.loadUrl(props.url).then(function(){
console.log("LOADED!");
})
}, [props.url]);
Inside my PlaylistObj class, I have an async function loadUrl(url) that
sets the apiLoading property of the playlist to true
gets content
sets the apiLoading property of the playlist to false
Now, I want to use that value in my React component, so I can set its classes (i'm using classnames) :
<div
className={classNames({
'api-loading': playlist.apiLoading
})}
>
But it doesn't work; the class is not updated, even if i DO get the "LOADED!" message in the console.
It seems that the playlist object is not "watched" by React. Maybe I should use react state here, but how ?
I tested
const [playlist, setPlaylist] = React.useState(new PlaylistObj());
React.useEffect(() => {
//refresh playlist if its URL is updated
playlist.loadUrl(props.playlistUrl).then(function(){
console.log("LOADED!");
})
}, [props.playlistUrl]);
And this, but it seems more and more unlogical to me, and, well, does not work.
const [playlist, setPlaylist] = React.useState(new PlaylistObj());
React.useEffect(() => {
playlist.loadUrl(props.playlistUrl).then(function(){
console.log("LOADED!");
setPlaylist(playlist); //added this
})
}, [props.playlistUrl]);
I just want my component be up-to-date with the playlist object. How should I handle this ?
I feel like I'm missing something.
Thanks a lot!
I think you are close, but basically this issue is you are not actually updating a state reference to trigger another rerender with the correct loading value.
const [playlist, setPlaylist] = React.useState(new PlaylistObj());
React.useEffect(() => {
playlist.loadUrl(props.playlistUrl).then(function(){
setPlaylist(playlist); // <-- this playlist reference doesn't change
})
}, [props.playlistUrl]);
I think you should introduce a second isLoading state to your component. When the effect is triggered whtn the URL updates, start by setting loading true, and when the Promise resolves update it back to false.
const [playlist] = React.useState(new PlaylistObj());
const [isloading, setIsLoading] = React.useState(false);
React.useEffect(() => {
setIsLoading(true);
playlist.loadUrl(props.playlistUrl).then(function(){
console.log("LOADED!");
setIsLoading(false);
});
}, [props.playlistUrl]);
Use the isLoading state in the render
<div
className={classNames({
'api-loading': isLoading,
})}
>
I also suggest using the finally block of a Promise chain to end the loading in the case that the Promise is rejected your UI doesn't get stuck in the loading "state".
React.useEffect(() => {
setIsLoading(true);
playlist.loadUrl(props.playlistUrl)
.then(function() {
console.log("LOADED!");
})
.finally(() => setIsLoading(false));
}, [props.playlistUrl]);
Here you go:
import React from "react";
class PlaylistAPI {
constructor(data = []) {
this.data = data;
this.listeners = [];
}
addListener(fn) {
this.listeners.push(fn);
}
removeEventListener(fn) {
this.listeners = this.listeners.filter(prevFn => prevFn !== fn)
}
setPlayList(data) {
this.data = data;
this.notif();
}
loadUrl(url) {
console.log("called loadUrl", url, this.data)
}
notif() {
this.listeners.forEach(fn => fn());
}
}
export default function App() {
const API = React.useMemo(() => new PlaylistAPI(), []);
React.useEffect(() => {
API.addListener(loadPlaylist);
/**
* Update your playlist and when user job has done, listerners will be called
*/
setTimeout(() => {
API.setPlayList([1,2,3])
}, 3000)
return () => {
API.removeEventListener(loadPlaylist);
}
}, [API])
function loadPlaylist() {
API.loadUrl("my url");
}
return (
<div className="App">
<h1>Watching an object by React Hooks</h1>
</div>
);
}
Demo in Codesandbox

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