Im using the google maps API for the first time and managed to finally get the map to render to the screen, I'm now working on adding markers of locations that I receive from elsewhere in my application. When I loop through the locations to get their respective lat and lng coordinates, I want to add them to my state variable. Currently the way I have my code, I am getting a response and it is being stored in my state variable, but it is only storing the most recent one rather than all of them.
Whats the best way to add all of these seperate responses from the API to my state variable?
Here is my code currently
export const MapRender =(props) => {
const {logs} = useContext(LogContext)
const [latLong, setLatLong] = useState([])
useEffect(()=>{
logs.map(l =>{
return fetch(`https://api.opencagedata.com/geocode/v1/json?q=${l.location}&key=MYKEY&limit=1`)
.then(res => res.json())
.then(parsedRes => setLatLong([parsedRes.results[0].geometry]))
})
},[logs])
console.log(latLong) --- returns a separate log for each response object, I want it to return one array with all responses
Updated
I didn't catch this when I first answered, having that cycle that sets the state on each iteration causes a lot of renders to be queued which leads to be the last incoming respobe the one to prevail.
The solution is to store all responses in one array and when all of them are finished you can set the state.
You may want to use this to know when all of the promises are done and then set the state.
Related
I am busy working on a "Headless" E-Commmerce Application in ReactJS and I Have stumbled upon an issue regarding performance.
My application uses a serverless approach with commercejs meaning I fetch my products and every other data via API calls instead of a traditional approach that involves me setting up a database and having other backend tools.
I already have this:
const App = () => {
const [products, setProducts ] = useState([]);
const getProducts = async () => {
const { data } = await commerce.products.list();
setProducts(data)
}
useEffect(() => {
getProducts()
},[])
}
Which is all used to get products and assign them to the products variable which I map through to display them inside divs and this works perfectly.
Here's what I need help with:
Is it be a good idea for me to use localStorage to store products instead of making a new commerce.products.list() every time the same user visits a page that need to display products?
Also, if so, how would one go about creating a function that knows when to update the products localStorage if there has been any changes (say a new product has been added or there's been price change for a certain product) if the products are now being fetched from localStorage?
Surely the answer to number 2, if is a yes, will be something like: make api requests that will be called on intervals but my main question/concern is how to know exactly when localStorage should be updated in an event like this without calling the API every now and then?
Also the use of sessionStorage did cross my mind, and it seemed like a better idea as the products data will be updated every time a user visits the application but I have considered the possibility of a user resuming a current window which was left open in the background for weeks and not see anything new.
I know this isn't a typical code/error/solution question but still any form of guidance/assistance will be highly appreciated.
I have a firebase database, that has a collection called "post" and in post there 6 variables (displayName, userName, verified, text, image, avatar). The idea is, there will be multiple posts in the database.
React Code:
const [posts, setPosts] = useState([]);
//Whenever the firebase database changes, it runs this method
useEffect(() => {
db.collection("posts").onSnapshot((snapshot) =>
//Loops through all the posts and adds the data into an array
setPosts(snapshot.docs.map((doc) => doc.data()))
);
}, []);
In react, I have two state variables, posts and setPosts. I'm assuming they are initially just set to empty arrays.
Now I have the useEffect function, that I am told runs whenever the database changes/updated. First question, how does the function know that the database updated? In other words, how does the useEffect function work?
Secondly, I'm pretty sure in the end, the post variable becomes a list of all the post objects in the database. I'm not sure how that happened. I have attached the code that updates this state above, but I'm not too sure how it works. Can you please break it down and explain how it works? I'm also not sure what the setPosts state is used for.
Please let me know!
In the above
In line 1 - You have used State hooks to set up posts as an empty Array. More reading can be done here to understand what state hooks mean - https://reactjs.org/docs/hooks-state.html
Next you set up a useEffect hook function (https://reactjs.org/docs/hooks-effect.html) to make a backend (firebase) api call after rendering.
Inside the hook function you are looking up data from the posts collection in firebase and bringing back a snapshot of all the documents in that collection. db.collection("posts").onSnapshot(callBack). The callback function is called every time something changes on the underlying database using well known observer pattern (read more in following links https://rxjs-dev.firebaseapp.com/guide/overview, https://firebase.google.com/docs/reference/node/firebase.firestore.CollectionReference#onsnapshot)
Then in the onSnapshot callback function you get an array containing documents which is further mapped to an output array using the javascript Map function snapshot.docs.map((doc) => doc.data()). https://www.w3schools.com/jsref/jsref_map.asp
Finally this output array is set in the posts variable using the
setPosts() method.
Hope this breakdown helps and I suggest reading the links in detail so its clear how everything comes together.
I've just started using Recoil on a new project and I'm not sure if there is a better way to accomplish this.
My app is an interface to basically edit a JSON file containing an array of objects. It reads the file in, groups the objects based on a specific property into tabs, and then a user can navigate the tabs, see the few hundred values per tab, make changes and then save the changes.
I'm using recoil because it allows me to access the state of each input from anywhere in my app, which makes saving much easier - in theory...
In order to generate State for each object in the JSON file, I've created an component that returns null and I map over the initial array, create the component, which creates Recoil state using an AtomFamily, and then also saves the ID to another piece of Recoil state so I can keep a list of everything.
Question 1 Is these a better way to do this? The null component doesn't feel right, but storing the whole array in a single piece of state causes a re-render of everything on every keypress.
To Save the data, I have a button which calls a function. That function just needs to get the ID's, loop through them, get the state of each one, and push them into an Array. I've done this with a Selector too, but the issue is that I can't call getRecoilValue from a function because of the Rules of Hooks - but if I make the value available to the parent component, it again slows everything right down.
Question 2 I'm pretty sure I'm missing the right way to think about storing state and using hooks, but I haven't found any samples for this particular use case - needing to generate the state up front, and then accessing it all again on Save. Any guidance?
Question 1
Get accustomed to null-rendering components, you almost can't avoid them with Recoil and, more in general, this hooks-first React world 😉
About the useRecoilValue inside a function: you're right, you should leverage useRecoilCallback for that kind of task. With useRecoilCallback you have a central point where you can get and set whatever you want at once. Take a look at this working CodeSandbox where I tried to replicate (the most minimal way) your use-case. The SaveData component (a dedicated component is not necessary, you could just expose the Recoil callback without creating an ad-hoc component) is the following
const SaveData = () => {
const saveData = useRecoilCallback(({ snapshot }) => async () => {
const ids = await snapshot.getPromise(carIds);
for (const carId of ids) {
const car = await snapshot.getPromise(cars(carId));
const carIndex = db.findIndex(({ id }) => id === carId);
db[carIndex] = car;
}
console.log("Data saved, new `db` is");
console.log(JSON.stringify(db, null, 2));
});
return <button onClick={saveData}>Save data</button>;
};
as you can see:
it retrieves all the ids through const ids = await snapshot.getPromise(carIds);
it uses the ids to retrieve all the cars from the atom family const car = await snapshot.getPromise(cars(carId));
All of that in a central point, without hooks and without subscribing the component to atoms updates.
Question 2
There are a few approaches for your use case:
creating empty atoms when the app starts, updating them, and saving them in the end. It's what my CodeSandbox does
doing the same but initializing the atoms through RecoilRoot' initialState prop
being updated by Recoil about every atom change. This is possible with useRecoilTransactionObserver but please, note that it's currently marked as unstable. A new way to do the same will be available soon (I guess) but at the moment it's the only solution
The latter is the "smarter" approach but it really depends on your use case, it's up to you to think if you really want to update the JSON at every atom' update 😉
I hope it helps, let me know if I missed something 😊
I have a problem and I'm pretty sure I'm not the only one who ever had it... Although I tried to find a solution, I didin't really find something that fits my purpose.
I won't post much code, since its not really a code problem, but more a logic problem.
Imagine I have the following hook:
useEffect(() => {
fetchFromApi(props.match.params.id);
}, [props.match.params.id]);
Imagine the result of fetchFromApi is displayed in a simple table in the UI.
Now lets say the user clicks on an entity in the navigation, so the ID prop in the browser URL changes and the effect triggers, leading to an API call. Lets say the call with this specific ID takes 5 seconds.
During this 5 seconds, the user again clicks on an element in the navigation, so the hook triggers again. This time, the API call only takes 0,1 seconds. The result is immediatly displayed.
But the first call is still running. Once its finished, it overwrites the current result, what leads to wrong data being displayed in the wrong navigation section.
Is there a easy way to solve this? I know I can't cancel promises by default, but I also know that there are ways to achieve it...
Also, it could be possible that fetchFromApi is not a single API call, but instead multiple calls to multiple endpoints, so the whole thing could become really tricky...
Thanks for any help.
The solution to this is extremely simple, you just have to determine whether the response that you got was from the latest API call or not and only then except it. You can do it by storing a triggerTime in ref. If the API call has been triggered another time, the ref will store a different value, however the closure variable will hold the same previously set value and it mean that another API call has been triggered after this and so we don't need to accept the current result.
const timer = useRef(null);
useEffect(() => {
fetchFromApi(props.match.params.id, timer);
}, [props.match.params.id]);
function fetchFromApi(id, timer) {
timer.current = Date.now();
const triggerTime = timer.current;
fetch('path').then(() => {
if(timer.current == triggerTime) {
// process result here
// accept response and update state
}
})
}
Other ways to handle such scenarios to the cancel the previously pending API requests. IF you use Axios it provides you with cancelToken that you can use, and similarly you can cancel XMLHttpRequests too.
I know Redux solves this but I came up with an idea.
Imagine I have an app that gets some JSON on start. Based on this JSON I'm setting up the environment, so let's assume the app starts and it downloads an array of list items.
Of course as I'm not using Redux (the app itself is quite simple and Redux feels like a huge overkill here) if I want to use these list items outside of my component I have to pass them down as props and then pass them as props again as deep as I want to use them.
Why can't I do something like this:
fetch(listItems)
.then(response => response.json())
.then(json => {
window.consts = json.list;
This way I can access my list anywhere in my app and even outside of React. Is it considered an anti-pattern? Of course the list items WON'T be changed EVER, so there is no interaction or change of state.
What I usually do when I have some static (but requested via API) data is a little service that acts kind like a global but is under a regular import:
// get-timezones.js
import { get } from '../services/request'
let fetching = false
let timez = null
export default () => {
// if we already got timezones, return it
if (timez) {
return new Promise((resolve) => resolve(timez))
}
// if we already fired a request, return its promise
if (fetching) {
return fetching
}
// first run, return request promise
// and populate timezones for caching
fetching = get('timezones').then((data) => {
timez = data
return timez
})
return fetching
}
And then in the view react component:
// some-view.js
getTimezones().then((timezones) => {
this.setState({ timezones })
})
This works in a way it will always return a promise but the first time it is called it will do the request to the API and get the data. Subsequent requests will use a cached variable (kinda like a global).
Your approach may have a few issues:
If react renders before this window.consts is populated you won't
be able to access it, react won't know it should re-render.
You seem to be doing this request even when the data won't be used.
The only downside of my approach is setting state asynchronously, it may lead to errors if the component is not mounted anymore.
From the React point of view:
You can pass the list from top level via Context and you can see docs here.
Sample of using it is simple and exists in many libraries, such as Material UI components using it to inject theme across all components.
From engineering concept of everything is a trade of:
If you feel that it's gonna take so much time, and you are not going to change it ever, so keep it simple, set it to window and document it. (For your self to not forget it and letting other people know why you did this.)
If you're absolutely certain they won't ever change, I think it's quite ok to store them in a global, especially if you need to access the data outside of React. You may want to use a different name, maybe something like "appNameConfig"..
Otherwise, React has a feature called Context, which can also be used for "deep provision" - Reference