React-Redux-notes.txt

What is Redux?
***************
Redux is a predictable state container for JavaScript apps.
> Redux is a library for JavaScript Applications.
> You can use Redux together with React, or with any other view library(Angular, Vue).
> Redux is a state container.
 Example- registration form

 Core Concepts of Redux
 ***********************
 Store ::➡ Holds state of your application.
 Action ::➡ Describe the changes in the state of application.
 Reducer ::➡ Actually carries out the state transition dependending on the action.

    Example ➡ Book Shop

Shop ➡➡➡➡➡➡ ShopKeeper ➡➡➡➡ Customer
(store)          (Reducer)          (action)

Rules of Redux
*****************
> The state of your application is stored in an object tree within a single store.
{
    NumberOfBooks : 10
}

> Only wayto change the state is to emit an action an object describing what happened.
{Type : "buyBook"}

> To specify how the state tree is transformed by actions, we write pure Reducer. 

How to install Redux in react app 
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to install redux in react use "npx install redux react-redux" command

Action in Redux
****************
> Actions are JavaScript object that contains information.
> Actions are the only source of information for the store. It only tells us what has happened.
> Actions have a type property and it should be defined in string consistraint.
> It is compulsory to include the type property in the object.

Syntax:
    const Actions = {
        Type : 'TypeOfAction'
    }


Reducers in React
******************
> Reducers decides how the state of application changes depending upon the action sent to the store.
> Reducers are the function that accepts state and action as parameter and returns the next state of the application.

    (previousState, action) => newState.


Redux Store
*************
> Entire Applicaton contains Single Store.
> It is responsible for holding application state.
> getState() method gives access to state it holds.
> dispatch(action) method allow state to be updated
> it has subscribe(listener) method as well by which we can register listeners.

    This methd accepts funtion (listener) as a parameter which execute anytime when the state in Redux store changes.


React Redux + Hooks
********************
React Redux offers set of hooks to - subscribe to redux store and dispatch actions.

useSelector Hook-
> useSelector is a hook react-redux library provides to get hold of any state that is maintained in the redux store.

Syntax - const xyz = useSelector(selector: function, equalityFn: function)

Selector function accepts the redux state as its argument and return a value.