Since React 18 introduced batch rendering in all places, we've been facing issues in our application. In our application, re-render needs to happen right away rather than batching. So we used flushSync() for every setState() call. Now we face an error/warning in the console "flushSync was called from inside a lifecycle method. React cannot flush them when React is already rendering. Consider moving this call to a scheduler task of the microtask". Is there any way we can use multiple setStates inside a handler and not have them batched?
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My questions is conceptual and that is we all know that using useEffect Hook, every time when useEffect calls after every render React cleans up use Effects from the previous render before running the effects next time and declares useEffect again with his new render. How useEffect maintains the previous state?.
Just google it. In short, react knows which components are mounting, mounted, etc. It keeps track of them all. Because it keeps track of them all, it can assign arbitrary data to each one. This is essentially what hooks are.
All hooks do is essentially provide a mechanism to allow instance variables (some form of internal state, but not "state" like you think in react) for functional components.
Iam new to React and i came across with this doc. It says that:
Either way, it is unsafe to use componentWillUpdate for this purpose
in async mode, because the external callback might get called multiple
times for a single update
How is it possible for the componentWillUpdate to be called multiple times? It doesnt explain it.
Thank you
Any change that is supposed to trigger a render will first go through a componentWillUpdate lifecycle. The change change can be a parent re-render causing the child to re-render, a change in components props, or a change in state.
However from v16.3.0 this lifecycle method is deprecated and it is encouraged that any sideeffect be handled in componentDidUpdate which will be triggered after render method.
On async mode, your component update/render may be postponed so react can deliver some hi-priority stuff. This means willUpdate will be called each time react starts working on your component, but it might not finish the full update, hence calling willUpdate every time it starts working on this component but only calls didUpdate once, after this process is finished.
I'm having an issue with data rendering properly within a Vue component. We have a scenario where we update the route, but it loads the same component. When this happens, it appears that the lifecycle hooks don't run. I assume that this is intentional and that Vue is trying to be performant.
I'm looking for a way to force the component to re-render giving me access to the lifecycle hooks again.
I am still learning React and I apologize if this is a stupid question. I am currently planning about the architecture of my simple App.
I am using Next.js for this project
I have a component that calls the third party API for data every 5 seconds. The data is shared among all pages in the app.
If the component that is fetching the data is not on the main/home page. Are there anyways for homepage to get the data it needs from another page?
For example [Below are all pages]
index.js // Plain simple page that displays current weather and top music
http://localhost:3000/
weatherforecast.js //Using componentDidMount every 5 seconds to fetch Weather Data
http://localhost:3000/weatherforecast
musicplaylist.js //Using componentDidMount every 5 seconds to fetch Weather
http://localhost:3000/musicplaylist
The data shown in homepage has to be refreshed every 5 seconds if there are changes to the following data in weatherforecast.js and musicplaylist.js
I had this in mind but I have a feeling that it's not the right way to do it.
In the Homepage.js, include WeatherForecast and MusicPlaylist components to fetch the data. If this is the case, it seems like I am repeating the same principle in every page.
I found out about Redux which store states as a global object. But how does the state know when to update. But before we getting to state, I am still not sure if components on another page can fetch the data without the user accessing the page.
Thanks for reading this question.
For a pure React solution, you need to utilize other lifecycle methods available for React. componentDidMount is a good spot for making API requests, so you're in the right place to start. However, componentDidMount occurs only once, right after the componentWillMount and after the DOM is ready with a complete render of the component. Setting your API call to run at a set interval will not trigger a rerender of the component, no any of it's sub components. Instead, use componentWillRecieveProps to add your interval request logic. After each interval completes, run setState with the new data from the request to update the default state defined in your constructor. As a bonus step to improve performace, follow up with function that returns a bool in componentShouldUpdate. This way you can strictly define how and when and what is causing any and all component re-rendering.
Redux is an excellent solution to take care of what you want to do. Personally always use it in my React projects to manage state. Using Redux, you could make your API calls still occur in componentDidMount, however the call can hook into your Redux store and update your initial state. The frees you up from have to worry about the local state of your component and how to go about conditionally rendering everything else in your app. Plus Redux abstracts other functions you need, like re-running your fetchToAPI in certain intervals, into their own source (known as Action Creators). Action Creators hook directly in the Redux store so that when one is used, the resulting state diff is passed to Redux's Reducers, which in turn update the application global state. Then all that needs to be done is to have all of your components that need re-rendering on global state change to listen for state changes that occur in the Redux store and conditionally re-render based on the diff of the store from prevState => newProps. This can be setup fairly easy using the boolean check in componentShouldUpdate.
Hope this helps! Cheers.
Redux passes the data throughout the connected components via prop, given that a component is mounted whenever it receives new props a new render cycle is initiated so it will reflect your changes, moreover if you dont want to use Redux you can try using the new context api which is easy to implement and will also be suitable for your solution here is a tutorial on how to use it
To pass data between pages in next.js you will have to use Redux. The idea of Redux is to have a single source of truth. In redux you update the state by calling actions. To update redux state you have to create something called action creators which dispatches action to update the state.
Answer to your question as to if components on another page can fetch data without the user accessing the page is that they do not need to access the data. The components are mounted only when they are accessed, so it will fetch the data when they are mounted.
Regarding the state change notification, refer to below image, and hopefully it is worth one thousand of words:
Original article here.
I am reading up on react lifecycle and am getting a little confused. Some recommend using componentWillMount to make ajax calls:
https://hashnode.com/post/why-is-it-a-bad-idea-to-call-setstate-immediately-after-componentdidmount-in-react-cim5vz8kn01flek53aqa22mby
Calling setState in componentDidMount will trigger another render()
call and it can lead to layout thrashing.
and in other places it says not to put ajax calls in the componentWillMount:
https://medium.com/#baphemot/understanding-reactjs-component-life-cycle-823a640b3e8d
...this function might end up being called multiple times before the
initial render is called so might result in triggering multiple
side-effects. Due to this fact it is not recommended to use this
function for any side-effect causing operations.
Which is correct?
The React docs recommend on using componentDidMount for making network Requests
componentDidMount() is invoked immediately after a component is
mounted. Initialization that requires DOM nodes should go here. If you
need to load data from a remote endpoint, this is a good place to
instantiate the network request.
Calling setState() in this method will trigger an extra rendering, but
it is guaranteed to flush during the same tick. This guarantees that
even though the render() will be called twice in this case, the user
won’t see the intermediate state.
As per the case for componentWillMount:
EDIT:
This lifecycle is deprecated since v16.3.0 of react and is no longer encouraged for usage.However its renamed to UNSAFE_componentWillUpdate and is expected to work till at least v17 of react
Before v16.3.0
An asynchronous call to fetch data will not return before the render happens. This means the component will render with empty data at least once.
There is no way to “pause” rendering to wait for data to arrive. You cannot return a promise from componentWillMount or wrangle in a setTimeout somehow. The right way to handle this is to setup the component’s initial state so that it’s valid for rendering.
To Sum it up
In practice, componentDidMount is the best place to put calls to fetch data, for two reasons:
Using DidMount makes it clear that data won’t be loaded until after
the initial render. This reminds you to set up initial state
properly, so you don’t end up with undefined state that causes
errors.
If you ever need to render your app on the server, componentWillMount will actually be
called twice – once on the server, and again on the client – which is
probably not what you want. Putting the data loading code in
componentDidMount will ensure that data is only fetched from the
client.
componentDidMount is the recommended lifecycle method to make Ajax calls as described in their docs
ComponentDidMount is the place.
But if you have time try to look at Redux and make the requests in actions, as your application grow it will help a lot to manage the app state.
;)