React integration testing, how to wait for page to be ready - reactjs

We have a web application written with React JS in the frontend and a PHP backend.
We are setting up Selenium integrated testing for the React frontend. In the past when we've done this for PHP applications, it is easy to wait for the page to be loaded before processing the assertions.
However in the React application, the web-browser doesn't actually change pages, instead the React renderer just renders the page differently.
Is there an easy way to tell if Reach is still busy fetching data from the server, and so the tests assertions need to wait?

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React and Next.js for server-side rendering

I'm new to React and have started working on a project which uses Next.js for server-side rendering. The application will also use Next.js for routing. I'm having trouble understanding at what point does the browser pull the application code from the server.
When the browser starts the application, is the entire application (in vanilla JS) pulled from the server at one time? Or are pieces of the application pulled from the server as needed as the user routes between different pages?

React App with PWA - Changes are not showing after deployment until hard refresh of the pages

We are using React Js and implemented PWA(Progressive Web App) using service workers. After each deployment to the server, the pages are not updated and we need to do hard refresh everytime. This is not the right way since we cannot inform the real time users to do hard refresh after each deployment. So please please solution on how to avoid hard refresh on react app with PWA

how to implement background tasks in react native using headless js so a fetch api runs indefinetely in all 3 states

how to run fetch api indefinitely in react native apps?
I am new to react native development but I found that I can keep a task running in android infinitely through headless Js. Is it the only way or there is another method? I just want to fetch api.
If headless JS does this task can someone explain how to do so since i am unable to understand their docs. It should satisfy{foreground/background/killed}.when there is data in api i need it to give a notification using react native notification

React Hydration - How can we hydrate a dynamic page that not fully available at build time?

I am building a website using Express and React. I go with Server-side rendering
Now I am looking for a solution to hydrate my final HTML.
The issue is at the build time, the page is still not available. A page only started with a main component and Express middlewares can add/remove sub-components to that main component. It means we only know what is the final structure of the page at the end of the request
Is there any way I can hydrate that page and make React available in the client browser?
Thank you so much

What happens with the state in a React isomorphic App

I am building an isomorphic app with React that must support users without JS.
I am new in this technology and I have a basic doubt:
The server can store the components states to emulate what React does in the client-side?
I imagine this flow when the user dont have JS:
The user click a button and send a request to the server.
The server recovers the state of the app and makes changes in it.
The components listen this changes and are rendered again.
Is it correct?
Assuming that you're using react-router :
The server aims to initialize your state, to provide it the default minimum values necessary to make your application work while getting an url.
For example, if you have an application in which you want to display a user list, let say on /users URL, when you'll send your first request, the server will store the users in the react state.
After that first load, you'll be working on the client side using react-router, and making XHR request.
However, if you refresh your page, the process will start again : first load initializing the state and then client side navigation.
EDIT : Explanations =>
When you want to use react on the server, this means that you use a Nodejs server. The fact is that react-dom provides a method called renderToString that transform a react jsx component into standard HTML.
This aims to load the first call faster
Why ?
When you load a "big" JS application on the client, you have some delay time, the time your browser needs to download your JS bundle.
Server side rendering aims to avoid that behaviour, or at least, to gives the feeling that the app starts faster.
In no case you can only use react, even if you use your server side renders. Why ? . Because your events on buttons, or asynchronous load on client, or keypress are in JS language.

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