I'm brand new to Redux and I'm trying to figure out the relationship between <Provider> and connect().
As I understand it, connect connects your component to the store. However, nowhere in the function arguments do you tell connect where exactly that store is!
If I'm not mistaken, the store is automagically provided to connect() by the <Provider>. This to me seems very counter-intuitive, because the entire point of Redux is to be transparent.
So my question is, how does <Provider> pass the store off to connect() without using some sort of global variable? Does it traverse the entire tree, searching for connected components and then inject itself? Is that not inefficient? And if so, how would I use two different stores within the same component tree?
Secondly, supposing I don't want to use <Provider>, how can I use connect() without it? i.e., how can I explicitly pass a store to each connected component?
<Provider> and connect are part of the react-redux module. They work together, you shouldn't really use one without the other. You can use redux on its own without react-redux, but you'll probably end up re-creating some or all of the features that react-redux provides.
react-redux works by using the React context. Context is like a hidden layer for passing variables that are shared by multiple components without explicitly passing them. To use context, you need to set the context somewhere, but also, any component that wants to use something from the context needs to get the variable. In react-redux <Provider> essentially saves the store to the context and connect provides a way to get the store from the context.
If you haven't already, I recommend these videos for getting started with Redux and react-redux from the creator of Redux.
The redux docs are pretty great and have some information regarding Provider and connect()
The option we recommend is to use a special React Redux component
called <Provider> to magically make the store available to all
container components in the application without passing it explicitly.
You only need to use it once when you render the root component
Essentially it leverages the use of context which is from React. As per the docs this allows you to pass data through the component tree without having to pass the props down manually at every level.
There's no reason why you can't explicitly pass the store. The idea here is that it just makes things easier.
Related
I am creating a React components library that exports a TypeScript function that another app can use. In that function, I need to retrieve some information from the app's store. How can I do this?
I cannot import the store and do store.getState() since I wouldn't know where the app's store is. Is there a way I can use connect() to do it?
If it's possible to design your function as a custom React hook, then you can use useSelector() inside it.
If it's not feasible, than shaping arguments to expect store been passed in - is a way. Especially if you are going to target older versions of react-redux, without useSelector
const[datas,setdatas]=useState("")
i have been using useState for storing variable and while finishing the last task my higher official told me to use Redux to store change and perform action . i read it in blog youtube videos but I can't quite get to know the necessary about redux. can someone suggest me a easy example or solution for me?
Thanking you in advance.
If you have a bunch of nested components in you app, you have to send props every time to the new nested component.
Then you feel like you want your states to be managed globally.
Otherwise you probably have to type same props again and again.
This is why Redux and other state managing modules are needed.
They put your state in a global storage and you can get that state in other component with props drilling. You only need to access global storage to get necessary state.
If your app has few components, redux or other state managing modules won't be necessary.
Redux provides a easy way to pass data through the component tree without having to pass props down manually at every level, and you should only use it for global states.
I think you can keep using useState for local states.
I would like to answer in 3 points
1. Understanding Redux
I found this (three principles) to be the most helpful way to begin understanding Redux.
https://redux.js.org/understanding/thinking-in-redux/three-principles
2. Why you have been asked to use redux?
Considering your senior has asked you to use Redux, I am assuming you are only coding a part of a larger app (already using redux) and the state in question needs to be a "global state" for use by multiple other components. If that's not the case please look at other solutions like react's context provider or simply using local state and passing it down with props where needed.
3. What else do you need to know?
If point 2 holds, I would urge you to check with your senior/team for the existing implementation of redux store, reducers, middleWare and devTools.
Note : I found redux to be a complex tool and could understand and appreciate it only after using it for a while.
I have a component which has some local state (form validation error messages). This component does not get its state from a parent, nor does it passes these values to any of its children.
My application uses Redux for global state management. Should I push this state to be managed via Redux, or keep using local state for this particular component.
The simple answer is NO. -Simply because you already have all the necessary data in the only relevant component where you're actually using it.
Redux (react-redux) is used for app level state management.
So, here comes the longer answer -If you at some point decide that you need the data in various components and also that they need/ should be accessible at any point, Redux is definitely a great option.
It all really depends on the amount of data and the need for effectively passing the data throughout the entire app.
On the other hand, if you only have to pass data between Parent - Children components, Redux could be an overkill, because you can still achieve it using just React by passing (exchange) values between various components via props.
So, if you only need that data inside only that component (Component level state), Redux it's a no-go because it's pretty large and it wouldn't be of any use for your case.
Sounds like the data is only needed for this component, so you don't need to push it to the Redux state.
Yes, if you take the way of an immutable state and connected components and you would avoid unecessary re-render.
In this case, you can connect your field to it's state, and rerender the error message only when an error occur.
I would not save this to Redux state.
Unless you require this data elsewhere.
I am new to react and redux. I have a scenario where there are nested components like this.
A > B > C > D
There is a property used in A component and it will be used in D component. So, I have two approaches:
Get state from redux store in component A and then pass it along as props to all it's child components even though it will be used only in D component.
I should connect to redux store in component D and fetch that property from there.
What is the correct approach?
As Dan Abramov, author of redux says in this issue
Both approaches of passing props down to children or connecting them
to the store are appropriate, however having nested connect()
components is actually going to give you more performance. The
downside is they're slightly more coupled to the application and
slightly harder to test, but that may not be a big issue.
He has also articulated a nice rule of thumb to follow on reddit
I do it this way:
Start by using one container and several presentational components
As presentational component tree grows, “middle” components start to pass too many props down
At this point, I wrap some leaf components into containers so that “middle” components don’t need to accept and pass down props that are
completely unrelated to them
Repeat
He has even tweeted regarding this:
Try to keep your presentation components separate. Create container
components by connecting them when it’s convenient.Whenever you feel like you’re duplicating code in parent components to provide data for same kinds of children, time to extract a container.
So in simple words:
You can use connect() at any level. Doing so makes the component smart, since it knows where its props come from. A dumb component just has props, and they could come from anywhere. A smart component is coupled to redux; a dumb component is not.
UPDATE: react-redux v7 and above
The same concept applies to useSelectors too. You can receive data in a container component and pass on to your presentational components, if multiple of its children make use of the same data
If however the data used by the children is different, you can choose to use useSelector individually within the child component. This will make sure that only those components re-render which actually need to
I would suggest if you are already using redux in your app then set the property in the redux store and fetch it in the component D.
But if the work flow is really simple and all the data is fetched from a single source per view, you can avoid redux as it is for complex state management.
What's the difference between A) using the connect method of connecting state and dispatch function to a component and B) simply having functions in a component that do the dispatching as well as accessing the store as a global directly?
(Not ES2015)
Quoting from the Redux FAQ on importing the store directly:
While you can reference your store instance by importing it directly, this is not a recommended pattern in Redux. If you create a store instance and export it from a module, it will become a singleton. This means it will be harder to isolate a Redux app as a component of a larger app, if this is ever necessary, or to enable server rendering, because on the server you want to create separate store instances for every request.
I also recently wrote a Reddit comment on why you should use React-Redux and connect instead of talking to the store directly. Quoting that:
First, while you can manually write the code to subscribe to the Redux store in your React components, there's absolutely no reason to write that code yourself. The wrapper components generated by React-Redux's connect function already have that store subscription logic taken care of for you.
Second, connect does a lot of work to ensure that your actual components only re-render when they actually need to. That includes lots of memoization work, and comparisons against the props from the parent component and the values returned by your mapStateToProps function for that component. By not using connect, you're giving up all those performance improvements, and your components will be unnecessarily re-rendering all the time.
Third, by only connecting your top-level component, you are also causing the rest of your app to re-render unnecessarily. The best performance pattern is to connect lots of components in your app, with each connected component only extracting the pieces of data it actually needs via mapStateToProps. That way, if any other data changes, that component won't re-render.
Fourth, you're manually importing the store into your components, and directly coupling them together, thus making it harder to test the components. I personally try to keep my components "unaware" of Redux. They never reference props.dispatch, but rather call pre-bound action creators like this.props.someFunction(). The component doesn't "know" that it's a Redux action creator - that function could be a callback from a parent component, a bound-up Redux action creator, or a mock function in a test, thus making the component more reusable and testable.
And finally, the vast majority of apps built using React and Redux use the React-Redux library. It's the official way to bind the two together, and doing anything else will just confuse other developers looking at your project.
For more info, see:
The Redux FAQ section on performance
The Redux FAQ entry on connecting multiple components
The Redux FAQ entry on components re-rendering too often
The Redux FAQ entry on importing the store directly
The Redux Performance section of my React/Redux links list
And finally, my blog posts Practical Redux, Part 6: Connected Lists, Forms, and Performance and Idiomatic Redux: Why use action creators?.
Source: I'm a Redux maintainer, and author of the Redux FAQ.