Develop Reference

Using variables instead of state

Is it still possible to render variables in react? Trying to use a more lightweight method of storing data on a component, but variables don't seem to render anymore in react. Is useRef the new method for variables or is it still possible in basic let variables.
Here is an example of variables not rendering in react:
https://codesandbox.io/s/serene-galileo-ml3f0?fontsize=14

You have a misconception about how React handles state. The reason why normal variables don't seem to work in React is actually an optimization. React only rerenders the elements on your page when absolutely necessary. The way you tell React "hey, my state changed, can you update the page to reflect that" is by using state variables. In your example, React only rerenders the elements that reference the b variable when you update it using setB. However, it does not rerender the elements that represent a when you update it using a++, because it has no way to detect that a was updated.
useState is actually more efficient than local variables, because it rerenders only what is necessary.

see virchau13's answer.
Although saving to a state is more intensive than a simple variable assignment, you have to take into account that what you see on the screen will only change via renders. So if you wanted to see the display increment on the screen, it will only do so via renders, which is most easily achieved through state changes.

Standard component interaction mechanisms vs Vuex - how to combine them?

The question is probably more theoretical.
I have little experience with Vue and am trying to figure out where my knowledge gaps are and fill them.
There are standard mechanisms for interaction between components:
from top to bottom - input parameters (props) are passed from parent components to child components
from bottom to top - events are thrown from child to parent
And on the other hand, there is VUEX with its own data storage, which is, roughly speaking, a global variable object with a set of methods for working with it.
Data from this storage is available at any time to any component. And it turns out that the use of Vuex seems to make the standard interaction mechanisms of components completely unnecessary.
Well, perhaps, the generation of events is still needed so that one component can quickly make it clear to the other about the completed action, events, etc.
The question is, does Vuex generally override the standard component interactions?
If it is not, how should it be combined in the right way?

I'll try to answer your question.
Vuex will be very usefull to store data that you'll need in a part of the application or globally, like user data.
If you can simply use $emit or props use it, it will be better and simple to understand the code, because it will be overkill to use the store just for "a prop".
So, you will use Vuex in your component to call an action and fetch / store some data you will need in a another view out of your children/parents context.
I don't know if my explanations are well haha, I tried :)

Can I pass Audio/Video object from expo-av into redux state?

I want to have a global Audio/Video object in my react-native application. I have a player and I want to manipulate music player in every side of my application. But I correctly dont know how I can create a global Audio/Video object and use functions like play/pause/setNewSong globally from different components. And my question is can I create redux store and pass audio object into store? Or maybe I must do it in another way. Thank you for answers

Don't put non-serializable values like class instances into the Redux store.
You should probably keep this near the root of your React component tree and make it accessible to the rest of the app using React's Context API.

React Component State management using redux

So Basically, I came across many articles where they are referring to manage state via flux or redux.
I wanted to know that how about UI component having its own state? Is it good practice to let redux manage the Api call and success toast messages etc. but UI components should have their own local state?
Kindly someone elaborate what is the best practice in industry?

Though the question calls for opinion, I am going to leave my answer. There is no standard best practice regarding this. It boils down to convenience and ground rules of your team, if there are more than one people writing the code.
I use Redux quite a lot. However, I won't refrain from using local state in components.
Form handling like input onChange handlers require local state. It is not performant to use global state for onChange handlers.
Reusable component uses local state. Again, it boils down to whether the reusability is a technical reusability or business reusability. If you are developing a custom scrollbar component, use local state. However, if you are using a comment form which is used everywhere in your application, use global state.
I prefer to have most of the stuff in global state. I use redux thunk as well. In redux thunk, it is possible to access global state within the thunk function. This is quite useful as it avoids the reliance for props / context being passed all around.
I do keep some simple things in local state -- for example, show / hide some stuff. I don't mind waiting for promises to resolve before hiding some stuff using local state.
Overall, the decision to use global state vs local state is primarily based on convenience. There are no standard rules other than what you and your team are comfortable with.
React is a way to declaratively deal with UI. There are some rules of the framework like state, props, context. It is left upto the developer to make the UI declarative and performant based on these primitives. How, a developer does it does not matter as long as the code is maintainable and understood by others.

After asking many professionals and industry developers, I came to know that managing state through redux depends on your application scope.
but more importantly, If I am working on enterprise Application then the application state must be managed through redux.
Now the question is what should be kept in our redux store. well, you can store almost anything in redux store but better to manage the local state of a component as well. for instance, opening a component Boolean should be managed in local state or any string or header name etc.

Good question! The answer is usually "it depends", but there are clear cases when you'd probably prefer to use one over the other.
Use Redux for storing state relevant to the application. E.g. the current page/panel that should be shown. As you mentioned, showing a notification/message - is something that'd make sense to store in redux state, as the alternative would be passing state all over the place, e.g. an error prop bubbling up to your root component which renders the toast message. Using thunk is also a good idea when you're fetching/manipulating data relevant to the whole app, e.g. a list of things that appear in several places.
Use component state for storing state only relevant to the component. That is, if you're filling in a form, it makes sense to store the value of text inputs, checkboxes etc. in your component state (perhaps in conjunction with container and presentational components) as the values at this point aren't relevant to the rest of the application.

Where is redux store saved?

I was looking into how secure a redux application can be, I am storing certain values in redux store i.e. user token etc.. and tried to see if someone else could gain access to them via an xss attack for example, I checked sessionStorage, localStorage, cookies and it is not there, as well as it is not inside my app.js file (my bundle file), hence my question.

Was just about to answer How does React and Redux store data? Is it localstorage or cookies? when it got closed as a duplicate. So I wanted to paste my answer here.
Answer
First off, it's worth noting that UI libraries don't actually manage state (other than component-level state). ReactJS and VueJS expect you to pass data to them like you would pass parameters to a function. They aren't concerned with where this data came from or how you're storing it.
Redux, on the other hand, is not a UI library -- it's a state management library. Redux does store state. The VueJS corollary to Redux would be "Vuex".
With that out of the way, the next thing you need to know is that there's a difference between state management and state persistence. Libraries like Redux and Vuex usually keep track of your variables and provide tools for changing state (reducers, specifically) - but they don't manage the persistence of that state. Persistence refers to saving the state somewhere to reload it the next time someone comes to your app - and seems to be what you're curious about (since you mentioned cookies and Local Storage)
Persistence is usually coded by hand (send the state to an API endpoint which saves it to a database, then when you reload the page you ping a different API endpoint to retrieve the state) or you utilize a plugin / module for your state manager to handle persistence for you. For example, there's a popular Redux Local Storage plugin called (trivially enough) redux-localstorage

From this part of documentation (http://redux.js.org/docs/FAQ.html#performance-state-memory) I deduce it's stored in memory, so it is not persistent.

The state in Redux is stored in memory. This means that, if you refresh the page the state gets wiped out. The state in redux is just a variable that persists in memory because it is referenced by all redux functions.
A misconception is:
In redux, we know that the state is stored as an object.
This is not correct. State in redux can be any valid JavaScript value, not just an object. It just usually makes the most sense for it to be an object (or a special object like an array) because that allows for a more flexible data structure (but you could make the state just be a number for example, according to your need).

Redux use internal memory for all data. For example, when you subscribe to Store, Redux just push listener to private array and do not use Cookies or LocalStorage.