I'm trying to restrict access to a admin area based on a int flag called isAdmin that is set to either 0 or 1 in my users table.
In the admin component I've made a function to fetch an API route that returns a unique user based on email, which will allow me to pass this parameter from the session to the API route - but it never returns true value
This is the code for the lookup function and how I restrict access in the component
export const getServerSideProps: GetServerSideProps = async () => {
const dashboards = await prisma.dashboard.findMany({
orderBy: {
id: "asc",
}
})
return {
props: JSON.parse(JSON.stringify({ dashboards })),
}
}
async function checkAdminUser(email: string) {
try {
const result = await fetch(`/api/user/${email}`, {
method: "GET",
})
const user = await result.json()
if (user.isAdmin == 1) {
return true
} else {
return false
}
} catch (error) {
console.error(error)
}
}
const Dashboard: React.FC<Props> = (props) => {
const { data: session, status } = useSession()
if (!session || !checkAdminUser(session.user?.email)) {
return (
<Layout>
<AccessDenied />
</Layout>
)
}
return (
<Layout>
..Layout code
</Layout>
)
}
I've also tried the checkAdminUser function as a Promise without success. The API route has been checked for valid output
"{"id":1,"image":null,"name":null,"email":"censoredfor#crawlers.com","emailVerified":null,"isAdmin":1,"createdAt":"2022-09-21T07:52:20.263Z","updatedAt":"2022-09-21T10:22:39.024Z"}"
Any tips to get me rolling would be greatly appreciated!
This answer assumes that console.log(user) gives you: {"id":1,"image":null,"name":null,"email":"censoredfor#crawlers.com","emailVerified":null,"isAdmin":1,"createdAt":"2022-09-21T07:52:20.263Z","updatedAt":"2022-09-21T10:22:39.024Z"}
Then you should better handle how you check if the user is an Admin. checkAdminUser returns a promise that is not resolved when you're checking for the value. A better solution would be to use react state to manage access to a specific component:
const Dashboard: React.FC<Props> = (props) => {
const { data: session, status } = useSession()
const [isAdmin, setAdmin] = useState(false);
const checkAdminUser = useCallback(async () => {
try {
const result = await fetch(`/api/user/${session?.user?.email}`, {
method: "GET",
})
const user = await result.json()
if (user.isAdmin == 1) {
setAdmin(true)
} else {
setAdmin(false)
}
} catch (error) {
console.error(error)
}
},[session?.user?.email])
useEffect(() => {
checkAdminUser()
},[checkAdminUser])
if (!session || !isAdmin) {
return (
<Layout>
<AccessDenied />
</Layout>
)
}
return (
<Layout>
..Layout code
</Layout>
)
}
Don't forget to: import {useCallback, useEffect, useState} from 'react'
I am trying to learn hooks and the useState method has made me confused. I am assigning an initial value to a state in the form of an array. The set method in useState is not working for me, both with and without the spread syntax.
I have made an API on another PC that I am calling and fetching the data which I want to set into the state.
Here is my code:
<div id="root"></div>
<script type="text/babel" defer>
// import React, { useState, useEffect } from "react";
// import ReactDOM from "react-dom";
const { useState, useEffect } = React; // web-browser variant
const StateSelector = () => {
const initialValue = [
{
category: "",
photo: "",
description: "",
id: 0,
name: "",
rating: 0
}
];
const [movies, setMovies] = useState(initialValue);
useEffect(() => {
(async function() {
try {
// const response = await fetch("http://192.168.1.164:5000/movies/display");
// const json = await response.json();
// const result = json.data.result;
const result = [
{
category: "cat1",
description: "desc1",
id: "1546514491119",
name: "randomname2",
photo: null,
rating: "3"
},
{
category: "cat2",
description: "desc1",
id: "1546837819818",
name: "randomname1",
rating: "5"
}
];
console.log("result =", result);
setMovies(result);
console.log("movies =", movies);
} catch (e) {
console.error(e);
}
})();
}, []);
return <p>hello</p>;
};
const rootElement = document.getElementById("root");
ReactDOM.render(<StateSelector />, rootElement);
</script>
<script src="https://unpkg.com/#babel/standalone#7/babel.min.js"></script>
<script src="https://unpkg.com/react#17/umd/react.production.min.js"></script>
<script src="https://unpkg.com/react-dom#17/umd/react-dom.production.min.js"></script>
Neither setMovies(result) nor setMovies(...result) works.
I expect the result variable to be pushed into the movies array.
Much like .setState() in class components created by extending React.Component or React.PureComponent, the state update using the updater provided by useState hook is also asynchronous, and will not be reflected immediately.
Also, the main issue here is not just the asynchronous nature but the fact that state values are used by functions based on their current closures, and state updates will reflect in the next re-render by which the existing closures are not affected, but new ones are created. Now in the current state, the values within hooks are obtained by existing closures, and when a re-render happens, the closures are updated based on whether the function is recreated again or not.
Even if you add a setTimeout the function, though the timeout will run after some time by which the re-render would have happened, the setTimeout will still use the value from its previous closure and not the updated one.
setMovies(result);
console.log(movies) // movies here will not be updated
If you want to perform an action on state update, you need to use the useEffect hook, much like using componentDidUpdate in class components since the setter returned by useState doesn't have a callback pattern
useEffect(() => {
// action on update of movies
}, [movies]);
As far as the syntax to update state is concerned, setMovies(result) will replace the previous movies value in the state with those available from the async request.
However, if you want to merge the response with the previously existing values, you must use the callback syntax of state updation along with the correct use of spread syntax like
setMovies(prevMovies => ([...prevMovies, ...result]));
Additional details to the previous answer:
While React's setState is asynchronous (both classes and hooks), and it's tempting to use that fact to explain the observed behavior, it is not the reason why it happens.
TLDR: The reason is a closure scope around an immutable const value.
Solutions:
read the value in render function (not inside nested functions):
useEffect(() => { setMovies(result) }, [])
console.log(movies)
add the variable into dependencies (and use the react-hooks/exhaustive-deps eslint rule):
useEffect(() => { setMovies(result) }, [])
useEffect(() => { console.log(movies) }, [movies])
use a temporary variable:
useEffect(() => {
const newMovies = result
console.log(newMovies)
setMovies(newMovies)
}, [])
use a mutable reference (if we don't need a state and only want to remember the value - updating a ref doesn't trigger re-render):
const moviesRef = useRef(initialValue)
useEffect(() => {
moviesRef.current = result
console.log(moviesRef.current)
}, [])
Explanation why it happens:
If async was the only reason, it would be possible to await setState().
However, both props and state are assumed to be unchanging during 1 render.
Treat this.state as if it were immutable.
With hooks, this assumption is enhanced by using constant values with the const keyword:
const [state, setState] = useState('initial')
The value might be different between 2 renders, but remains a constant inside the render itself and inside any closures (functions that live longer even after render is finished, e.g. useEffect, event handlers, inside any Promise or setTimeout).
Consider following fake, but synchronous, React-like implementation:
// sync implementation:
let internalState
let renderAgain
const setState = (updateFn) => {
internalState = updateFn(internalState)
renderAgain()
}
const useState = (defaultState) => {
if (!internalState) {
internalState = defaultState
}
return [internalState, setState]
}
const render = (component, node) => {
const {html, handleClick} = component()
node.innerHTML = html
renderAgain = () => render(component, node)
return handleClick
}
// test:
const MyComponent = () => {
const [x, setX] = useState(1)
console.log('in render:', x) // ✅
const handleClick = () => {
setX(current => current + 1)
console.log('in handler/effect/Promise/setTimeout:', x) // ❌ NOT updated
}
return {
html: `<button>${x}</button>`,
handleClick
}
}
const triggerClick = render(MyComponent, document.getElementById('root'))
triggerClick()
triggerClick()
triggerClick()
<div id="root"></div>
I know that there are already very good answers. But I want to give another idea how to solve the same issue, and access the latest 'movie' state, using my module react-useStateRef.
As you understand by using React state you can render the page every time the state change. But by using React ref, you can always get the latest values.
So the module react-useStateRef let you use state's and ref's together. It's backward compatible with React.useState, so you can just replace the import statement
const { useEffect } = React
import { useState } from 'react-usestateref'
const [movies, setMovies] = useState(initialValue);
useEffect(() => {
(async function() {
try {
const result = [
{
id: "1546514491119",
},
];
console.log("result =", result);
setMovies(result);
console.log("movies =", movies.current); // will give you the latest results
} catch (e) {
console.error(e);
}
})();
}, []);
More information:
react-usestsateref
I just finished a rewrite with useReducer, following #kentcdobs article (ref below) which really gave me a solid result that suffers not one bit from these closure problems.
See: https://kentcdodds.com/blog/how-to-use-react-context-effectively
I condensed his readable boilerplate to my preferred level of DRYness -- reading his sandbox implementation will show you how it actually works.
import React from 'react'
// ref: https://kentcdodds.com/blog/how-to-use-react-context-effectively
const ApplicationDispatch = React.createContext()
const ApplicationContext = React.createContext()
function stateReducer(state, action) {
if (state.hasOwnProperty(action.type)) {
return { ...state, [action.type]: state[action.type] = action.newValue };
}
throw new Error(`Unhandled action type: ${action.type}`);
}
const initialState = {
keyCode: '',
testCode: '',
testMode: false,
phoneNumber: '',
resultCode: null,
mobileInfo: '',
configName: '',
appConfig: {},
};
function DispatchProvider({ children }) {
const [state, dispatch] = React.useReducer(stateReducer, initialState);
return (
<ApplicationDispatch.Provider value={dispatch}>
<ApplicationContext.Provider value={state}>
{children}
</ApplicationContext.Provider>
</ApplicationDispatch.Provider>
)
}
function useDispatchable(stateName) {
const context = React.useContext(ApplicationContext);
const dispatch = React.useContext(ApplicationDispatch);
return [context[stateName], newValue => dispatch({ type: stateName, newValue })];
}
function useKeyCode() { return useDispatchable('keyCode'); }
function useTestCode() { return useDispatchable('testCode'); }
function useTestMode() { return useDispatchable('testMode'); }
function usePhoneNumber() { return useDispatchable('phoneNumber'); }
function useResultCode() { return useDispatchable('resultCode'); }
function useMobileInfo() { return useDispatchable('mobileInfo'); }
function useConfigName() { return useDispatchable('configName'); }
function useAppConfig() { return useDispatchable('appConfig'); }
export {
DispatchProvider,
useKeyCode,
useTestCode,
useTestMode,
usePhoneNumber,
useResultCode,
useMobileInfo,
useConfigName,
useAppConfig,
}
With a usage similar to this:
import { useHistory } from "react-router-dom";
// https://react-bootstrap.github.io/components/alerts
import { Container, Row } from 'react-bootstrap';
import { useAppConfig, useKeyCode, usePhoneNumber } from '../../ApplicationDispatchProvider';
import { ControlSet } from '../../components/control-set';
import { keypadClass } from '../../utils/style-utils';
import { MaskedEntry } from '../../components/masked-entry';
import { Messaging } from '../../components/messaging';
import { SimpleKeypad, HandleKeyPress, ALT_ID } from '../../components/simple-keypad';
export const AltIdPage = () => {
const history = useHistory();
const [keyCode, setKeyCode] = useKeyCode();
const [phoneNumber, setPhoneNumber] = usePhoneNumber();
const [appConfig, setAppConfig] = useAppConfig();
const keyPressed = btn => {
const maxLen = appConfig.phoneNumberEntry.entryLen;
const newValue = HandleKeyPress(btn, phoneNumber).slice(0, maxLen);
setPhoneNumber(newValue);
}
const doSubmit = () => {
history.push('s');
}
const disableBtns = phoneNumber.length < appConfig.phoneNumberEntry.entryLen;
return (
<Container fluid className="text-center">
<Row>
<Messaging {...{ msgColors: appConfig.pageColors, msgLines: appConfig.entryMsgs.altIdMsgs }} />
</Row>
<Row>
<MaskedEntry {...{ ...appConfig.phoneNumberEntry, entryColors: appConfig.pageColors, entryLine: phoneNumber }} />
</Row>
<Row>
<SimpleKeypad {...{ keyboardName: ALT_ID, themeName: appConfig.keyTheme, keyPressed, styleClass: keypadClass }} />
</Row>
<Row>
<ControlSet {...{ btnColors: appConfig.buttonColors, disabled: disableBtns, btns: [{ text: 'Submit', click: doSubmit }] }} />
</Row>
</Container>
);
};
AltIdPage.propTypes = {};
Now everything persists smoothly everywhere across all my pages
React's useEffect has its own state/lifecycle. It's related to mutation of state, and it will not update the state until the effect is destroyed.
Just pass a single argument in parameters state or leave it a black array and it will work perfectly.
React.useEffect(() => {
console.log("effect");
(async () => {
try {
let result = await fetch("/query/countries");
const res = await result.json();
let result1 = await fetch("/query/projects");
const res1 = await result1.json();
let result11 = await fetch("/query/regions");
const res11 = await result11.json();
setData({
countries: res,
projects: res1,
regions: res11
});
} catch {}
})(data)
}, [setData])
# or use this
useEffect(() => {
(async () => {
try {
await Promise.all([
fetch("/query/countries").then((response) => response.json()),
fetch("/query/projects").then((response) => response.json()),
fetch("/query/regions").then((response) => response.json())
]).then(([country, project, region]) => {
// console.log(country, project, region);
setData({
countries: country,
projects: project,
regions: region
});
})
} catch {
console.log("data fetch error")
}
})()
}, [setData]);
Alternatively, you can try React.useRef() for instant change in the React hook.
const movies = React.useRef(null);
useEffect(() => {
movies.current='values';
console.log(movies.current)
}, [])
The closure is not the only reason.
Based on the source code of useState (simplified below). Seems to me the value is never assigned right away.
What happens is that an update action is queued when you invoke setValue. And after the schedule kicks in and only when you get to the next render, these update action then is applied to that state.
Which means even we don't have closure issue, react version of useState is not going to give you the new value right away. The new value doesn't even exist until next render.
function useState(initialState) {
let hook;
...
let baseState = hook.memoizedState;
if (hook.queue.pending) {
let firstUpdate = hook.queue.pending.next;
do {
const action = firstUpdate.action;
baseState = action(baseState); // setValue HERE
firstUpdate = firstUpdate.next;
} while (firstUpdate !== hook.queue.pending);
hook.queue.pending = null;
}
hook.memoizedState = baseState;
return [baseState, dispatchAction.bind(null, hook.queue)];
}
function dispatchAction(queue, action) {
const update = {
action,
next: null
};
if (queue.pending === null) {
update.next = update;
} else {
update.next = queue.pending.next;
queue.pending.next = update;
}
queue.pending = update;
isMount = false;
workInProgressHook = fiber.memoizedState;
schedule();
}
There's also an article explaining the above in the similar way, https://dev.to/adamklein/we-don-t-know-how-react-state-hook-works-1lp8
I too was stuck with the same problem. As other answers above have clarified the error here, which is that useState is asynchronous and you are trying to use the value just after setState. It is not updating on the console.log() part because of the asynchronous nature of setState, it lets your further code to execute, while the value updating happens on the background. Thus you are getting the previous value. When the setState is completed on the background it will update the value and you will have access to that value on the next render.
If anyone is interested to understand this in detail. Here is a really good Conference talk on the topic.
https://www.youtube.com/watch?v=8aGhZQkoFbQ
I found this to be good. Instead of defining state (approach 1) as, example,
const initialValue = 1;
const [state,setState] = useState(initialValue)
Try this approach (approach 2),
const [state = initialValue,setState] = useState()
This resolved the rerender issue without using useEffect since we are not concerned with its internal closure approach with this case.
P.S.: If you are concerned with using old state for any use case then useState with useEffect needs to be used since it will need to have that state, so approach 1 shall be used in this situation.
If we have to update state only, then a better way can be if we use the push method to do so.
Here is my code. I want to store URLs from Firebase in state.
const [imageUrl, setImageUrl] = useState([]);
const [reload, setReload] = useState(0);
useEffect(() => {
if (reload === 4) {
downloadUrl1();
}
}, [reload]);
const downloadUrl = async () => {
setImages([]);
try {
for (let i = 0; i < images.length; i++) {
let url = await storage().ref(urls[i].path).getDownloadURL();
imageUrl.push(url);
setImageUrl([...imageUrl]);
console.log(url, 'check', urls.length, 'length', imageUrl.length);
}
}
catch (e) {
console.log(e);
}
};
const handleSubmit = async () => {
setReload(4);
await downloadUrl();
console.log(imageUrl);
console.log('post submitted');
};
This code works to put URLs in state as an array. This might also work for you.
With custom hooks from my library, you can wait for the state values to update:
useAsyncWatcher(...values):watcherFn(peekPrevValue: boolean)=>Promise - is a promise wrapper around useEffect that can wait for updates and return a new value and possibly a previous one if the optional peekPrevValue argument is set to true.
(Live Demo)
import React, { useState, useEffect, useCallback } from "react";
import { useAsyncWatcher } from "use-async-effect2";
function TestComponent(props) {
const [counter, setCounter] = useState(0);
const [text, setText] = useState("");
const textWatcher = useAsyncWatcher(text);
useEffect(() => {
setText(`Counter: ${counter}`);
}, [counter]);
const inc = useCallback(() => {
(async () => {
await new Promise((resolve) => setTimeout(resolve, 1000));
setCounter((counter) => counter + 1);
const updatedText = await textWatcher();
console.log(updatedText);
})();
}, []);
return (
<div className="component">
<div className="caption">useAsyncEffect demo</div>
<div>{counter}</div>
<button onClick={inc}>Inc counter</button>
</div>
);
}
export default TestComponent;
useAsyncDeepState is a deep state implementation (similar to this.setState (patchObject)) whose setter can return a promise synchronized with the internal effect. If the setter is called with no arguments, it does not change the state values, but simply subscribes to state updates. In this case, you can get the state value from anywhere inside your component, since function closures are no longer a hindrance.
(Live Demo)
import React, { useCallback, useEffect } from "react";
import { useAsyncDeepState } from "use-async-effect2";
function TestComponent(props) {
const [state, setState] = useAsyncDeepState({
counter: 0,
computedCounter: 0
});
useEffect(() => {
setState(({ counter }) => ({
computedCounter: counter * 2
}));
}, [state.counter]);
const inc = useCallback(() => {
(async () => {
await new Promise((resolve) => setTimeout(resolve, 1000));
await setState(({ counter }) => ({ counter: counter + 1 }));
console.log("computedCounter=", state.computedCounter);
})();
});
return (
<div className="component">
<div className="caption">useAsyncDeepState demo</div>
<div>state.counter : {state.counter}</div>
<div>state.computedCounter : {state.computedCounter}</div>
<button onClick={() => inc()}>Inc counter</button>
</div>
);
}
var [state,setState]=useState(defaultValue)
useEffect(()=>{
var updatedState
setState(currentState=>{ // Do not change the state by get the updated state
updateState=currentState
return currentState
})
alert(updateState) // the current state.
})
Without any addtional NPM package
//...
const BackendPageListing = () => {
const [ myData, setMyData] = useState( {
id: 1,
content: "abc"
})
const myFunction = ( x ) => {
setPagenateInfo({
...myData,
content: x
})
console.log(myData) // not reflecting change immediately
let myDataNew = {...myData, content: x };
console.log(myDataNew) // Reflecting change immediately
}
return (
<>
<button onClick={()=>{ myFunction("New Content")} }>Update MyData</button>
</>
)
Not saying to do this, but it isn't hard to do what the OP asked without useEffect.
Use a promise to resolve the new state in the body of the setter function:
const getState = <T>(
setState: React.Dispatch<React.SetStateAction<T>>
): Promise<T> => {
return new Promise((resolve) => {
setState((currentState: T) => {
resolve(currentState);
return currentState;
});
});
};
And this is how you use it (example shows the comparison between count and outOfSyncCount/syncCount in the UI rendering):
const App: React.FC = () => {
const [count, setCount] = useState(0);
const [outOfSyncCount, setOutOfSyncCount] = useState(0);
const [syncCount, setSyncCount] = useState(0);
const handleOnClick = async () => {
setCount(count + 1);
// Doesn't work
setOutOfSyncCount(count);
// Works
const newCount = await getState(setCount);
setSyncCount(newCount);
};
return (
<>
<h2>Count = {count}</h2>
<h2>Synced count = {syncCount}</h2>
<h2>Out of sync count = {outOfSyncCount}</h2>
<button onClick={handleOnClick}>Increment</button>
</>
);
};
Use the Background Timer library. It solved my problem.
const timeoutId = BackgroundTimer.setTimeout(() => {
// This will be executed once after 1 seconds
// even when the application is the background
console.log('tac');
}, 1000);
// replace
return <p>hello</p>;
// with
return <p>{JSON.stringify(movies)}</p>;
Now you should see, that your code actually does work. What does not work is the console.log(movies). This is because movies points to the old state. If you move your console.log(movies) outside of useEffect, right above the return, you will see the updated movies object.
I am using nextJS SSR in my project. Now when I try to use the following code to get page parameters then it shows undefined.
function About() {
const router = useRouter();
const { plan_id } = router.query;
console.log(plan_id)
}
export default About;
It works when the page is routed from some other page (without page reload with "next/link") but it does not work when I refresh the page. Can someone please help?
I found the answer self. Actually when you refresh the page then the router does not get initialized instantly. So you can add that under UseEffect hook as following and you will be able to get the parameters
function About() {
const [param1, setParam1]=useState("");
const router = useRouter();
useEffect(() => {
if (router && router.query) {
console.log(router.query);
setParam1(router.query.param1);
}
}, [router]);
}
When this router parameter will change then it will call the "UseEffect" which can be used to retrieve the values.
function About({plan_id}) {
console.log(plan_id)
}
// this function only runs on the server by Next.js
export const getServerSideProps = async ({params}) => {
const plan_id = params.plan_id;
return {
props: { plan_id }
}
}
export default About;
You can find more intel in the docs.
I fix this problem with this method.
First add getServerSideProps to your page
//MyPage.js
export async function getServerSideProps({req, query}) {
return {
props: {
initQuery: query
}
}
}
Then created useQuery function like this
//useQuery.js
export let firstQuery = {}
export default function useQuery({slugKey = 'slug', initial = {}} = {}) {
const {query = (initial || firstQuery)} = useRouter()
useEffect(() => {
if (_.isEmpty(initial) || !_.isObject(initial))
return
firstQuery = initial
}, [initial])
return useMemo(() => {
if (!_.isEmpty(query)) {
return query
}
try {
const qs = window.location.search.split('+').join(' ');
const href = window.location.href
const slug = href.substring(href.lastIndexOf('/') + 1).replace(/\?.*/gi, '')
let params = {},
tokens,
re = /[?&]?([^=]+)=([^&]*)/g;
if (slug)
params[slugKey] = slug
while (tokens = re.exec(qs)) {
params[decodeURIComponent(tokens[1])] = decodeURIComponent(tokens[2]);
}
return params
} catch {
}
}, [query])
}
And always use useQuery for receive query params
//MyPage.js
export default function MyPage({initQuery}) {
const query = useQuery({initial: initQuery})
return(
<div>
{query.myParam}
</div>
)
}
And in components like this
//MyComponent.js
export default function MyComponent() {
const query = useQuery()
return(
<div>
{query.myParam}
</div>
)
}
For those still having issues with this. Here is a solution that worked for me
function About() {
const [param1, setParam1]=useState("");
const router = useRouter();
const { param1 } = router.query()
useEffect(() => {
if (!param1) {
return;
}
// use param1
}, [param1]);
}
You can find the solution here
I have an issue where I have a simple React.Context that's populated after all the components mount. The problem is that because it happens after mount, nextjs does not see this data on initial render, and so there's noticeable flicker.
Here's the simple component that sets the Context:
export const SetTableOfContents = (props: { item: TableOfContentsItem }) => {
const toc = useContext(TableOfContentsContext);
useEffect(() => {
// Updates the React.Context after the component mount
// (since useEffects run after mount)
toc.setItem(props.item);
}, [props.item, toc]);
return null;
};
Here's the React.Context. It uses React state to store the TOC items.
export const TableOfContentsProvider = (props: {
children?: React.ReactNode;
}) => {
const [items, setItems] = useState<TableOfContents["items"]>([]);
const value = useMemo(() => {
return {
items,
setItem(item: TableOfContentsItem) {
setItems((items) => items.concat(item));
},
};
}, [items]);
return (
<TableOfContentsContext.Provider value={value}>
{props.children}
</TableOfContentsContext.Provider>
);
};
Currently, it is not possible to set the React.Context before mount because React gives a warning---Cannot update state while render.
The only workaround I can think of is to use something other than React.state for the React.Context state---that way the component can update it any time it wants. But then the problem with that approach is that Context Consumers would no longer know that the items changed (because updates live outside the React lifecycle)!
So how to get the initial React.Context into the initial SSR render?
const items = [];
export const TableOfContentsProvider = (props: {
children?: React.ReactNode;
}) => {
const value = useMemo(() => {
return {
items,
setItem(item: TableOfContentsItem) {
items[item.index] = item;
},
};
// this dep never changes.
// when you call this function, values never change
}, [items]);
return (
<TableOfContentsContext.Provider value={value}>
{props.children}
</TableOfContentsContext.Provider>
);
};
Here's what I ended up doing:
render the app in getStaticProps using renderToString
use useRef for state in the Context instead of useState
the reason for doing this is because renderToString renders only the initial state. So if you update the Context using useState, it won't capture subsequent renders
update the Context on component initialization for the reason mentioned above
pass the Context an "escape hatch"---a function we can call to get the state calculated on the initial render
Yes, the whole thing seems like a giant hack! :-) I'm not sure if React.Context plays well with SSR :(
export const TableOfContentsProvider = (props: {
initialItems?: TableOfContentsItem[];
setItemsForSSR?: (items: TableOfContentsItem[]) => void;
children?: React.ReactNode;
}) => {
// use useRef for the reasons mentioned above
const items = useRef(props.initialItems || []);
// Client still needs to see updates, so that's what this is for
const [count, setCount] = useState(0);
const { setItemsForSSR } = props;
const setterValue = useMemo(
() => ({
setItem(item: TableOfContentsItem) {
if (!items.current.find((x) => x.id === item.id)) {
items.current.push(item);
items.current.sort((a, b) => a.index - b.index);
setCount((count) => count + 1);
setItemsForSSR?.(items.current);
}
},
}),
[setItemsForSSR]
);
const stateValue = useMemo(() => ({ items: items.current, count }), [count]);
return (
<TableOfContentsSetterContext.Provider value={setterValue}>
<TableOfContentsStateContext.Provider value={stateValue}>
{props.children}
</TableOfContentsStateContext.Provider>
</TableOfContentsSetterContext.Provider>
);
};
interface TableOfContentsSetterWorkerProps {
item: TableOfContentsItem;
setItem: (item: TableOfContentsItem) => void;
}
export class TableOfContentsSetterWorker extends React.Component<
TableOfContentsSetterWorkerProps,
{}
> {
constructor(props: TableOfContentsSetterWorkerProps) {
super(props);
// Need to do this on init otherwise renderToString won't record it
props.setItem(props.item);
}
render() {
return null;
}
}
/**
* Usage: use this as a child component when the parent needs to set the TOC.
*
* Exists so that a component can set the TOC without triggering
* an unnecessary render on itself.
*/
export function TableOfContentsSetter(props: { item: TableOfContentsItem }) {
const { setItem } = useContext(TableOfContentsSetterContext);
return <TableOfContentsSetterWorker item={props.item} setItem={setItem} />;
export const getStaticProps = async () => {
let initialTableOfContents: TableOfContentsItem[] = [];
const getItems = (items: TableOfContentsItem[]) => {
initialTableOfContents = [...items];
};
const app = () => (
<TableOfContentsProvider setItemsForSSR={getItems}>
<AppArticles />
</TableOfContentsProvider>
);
renderToString(app());
return {
props: {
initialTableOfContents,
},
};
};