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An EXAMPLE of how reducers are USED in Redux is GIVEN below:

Reducers in Redux's architecture are PURE functions that are used to TAKE the previous state and an action and RETURN the NEXT state. Its syntax is given below:

First of all, we can store all the constants in a single file in our project NAMED constants.js or SOMETHING else as follows:

After storing the constants in one place, we can use them in two ways in our project:

• During actions creation (in actions.js file of our project):

• In Reducers (in reducer.js file of our project):

Constants in REDUX help us in easily finding all the usages of a PARTICULAR functionality across our entire project when we are using an Integrated Development Environment (IDE). Using constants, we can avoid SILLY bugs CAUSED because of typing ERRORS or typos as it shows a "ReferenceError" whenever a typo is made.

Redux is primarily being used ALONG with React. However, we can also USE it along with ANGULAR, Vue, Meteor, ETC. USING the bindings it has to offer to us.

An EXAMPLE of the usage of ACTIONS in Redux's architecture is GIVEN below:

In the Redux architecture, actions are NOTHING but the plain JavaScript objects which contain a type field. They can be thought of as an event that is used to DESCRIBE SOMETHING which has HAPPENED in the application. Actions contain only a tiny bit of information that is required to mention what has happened.

The key differences between MAPSTATETOPROPS() and mapDispatchToProps() are given below:

No, it is not NECESSARY to keep all the component states in the REDUX store. We have to keep your application STATE as small as possible and therefore, we should do it only if it MAKES a difference for us to keep something there or MAYBE if it makes the use of Dev Tools easier.

Some of the major features of Redux DevTools are as follows:

• Redux DevTools is nothing but a time travel ENVIRONMENT that makes it POSSIBLE for US to live edit in Redux with a variety of functionalities like action replay, hot reloading, and customizable UI.
• Redux DevTools makes it possible for us to inspect all the states and action payload. We can go back into the time simply by cancelling the actions.
• Each STAGE action is re-evaluated in case we change the code of the reducer.
• We can also continue our debug sessions across page reloads with the HELP of persistState() store enhancer.

REDUX Toolkit is Redux's official, opinionated, batteries included TOOLSET for efficient Redux development. It ALSO consists of the most widely used Redux add-ons, for instance, Redux Thunk for asynchronous logic,  Reselect for WRITING selector functions and many more for making development easy for developers and saving them TIME.

No, it is not true that Redux can only be used with REACT. Redux is being used as a data store for lots of UI layers. There are BINDINGS AVAILABLE in Redux for React, Angular, Angular 2, Vue, etc. 

Some of the ADVANTAGES of USING Redux are as follows:

• Redux provides extremely easy state transfer between the components.
• The states are ALWAYS predictable in Redux and its maintenance is relatively easy.
• Debugging and testing code in Redux is simple through logging behaviour and status.
• Redux provides great performance. It might occur to us that KEEPING the application's state global would result in bad performance. However, usually, that is not the case as React Redux IMPLEMENTS a lot of performance optimizations internally so that our own connected component only re-renders when it actually needs to.
• Redux also offers state persistence by storing the application's state to local storage and restoring it after a refresh.

The core principles of Redux are as follows:

• SINGLE source of truth: The global state of our application is always put away in an object tree inside one store.
• The state is read-only: The only way to change the state of our application is by EMITTING an action, an object explaining what has happened.
• Changes are made with PURE functions: This PRINCIPLE means that in order to define how the state tree is being TRANSFORMED by the actions, we have to write pure reducers.

Redux in React is the official React binding for Redux which allows the COMPONENTS in React to read data from a Redux Store, and dispatch Actions to the Store for updating the data. The PURPOSE of Redux is to help applications scale well by providing means to MANAGE the state via a UNIDIRECTIONAL data FLOW model. 

The main differences in the comparison: Redux vs Flux are as follows:

FLUX is an application design PARADIGM just like the Model View Controller design pattern. Flux is nothing but a new kind of architecture that complements React and the concept of Unidirectional Data Flow. The image given below shows how the workflow between dispatcher, STORES and VIEWS components with distinct inputs and OUTPUTS are in Flux:

Redux is an open-source library made using the scripting language JavaScript. Redux's primary use LIES in managing and centralizing APPLICATION state and it is usually USED along with JavaScript libraries, for instance, React or Angular in order to build UIs (User Interfaces). It is a PREDICTABLE state container for applications built using JavaScript. It is based on the FLUX design pattern. Redux is very small in size (around 2 kilobytes) and has no dependencies.