Explore topic-wise InterviewSolutions in .

In ORDER to add multiple middlewares to Redux, the usage of APPLYMIDDLEWARE can do the work. In applyMiddleware, we can pass every piece of middleware as a new argument. Therefore, our job is to just pass each piece of middleware that we want. In the example given below, we have added Redux Thunk and logger middlewares as an argument:

The purpose of this article was to explain to our readers what Redux actually is, what is it used for and what are the most important questions asked in the interviews. It is one of the most important JavaScript libraries which is being used alongside REACT for building a number of applications seamlessly and therefore, we would suggest that any budding talent of today should be familiar with the concepts of Redux to get an edge over others. 

Given below are some of the REFERENCES and recommended resources to learn more about Redux:

• Redux Documentation and API usages
• Redux Github
• For using Redux with Node Package Manager - NPM
• React
• Angular

The things which we should never do inside a reducer are as follows:

• MODIFY the argument of the reducer
• We should assure that we do not perform any SIDE operations such as routing TRANSITIONS, API calls, etc.
• We should not CALL non-pure functions, for instance Date.now(), Math.random(), etc.

Redux Saga is a middleware LIBRARY that can be useful for allowing a Redux store to interact with the resources outside of itself in an asynchronous manner, for example, making HTTP REQUESTS to external services, accessing browser storage, executing Input/Output operations and many more. These operations are also called side effects.

The KEY differences in the comparison: Context Api VS Redux are as follows:

For accessing a redux STORE outside a REACT COMPONENT, we can export the store from the module where it has been CREATED with createStore as done in the following EXAMPLE:

EVERY Redux application has multiple top-level directories as GIVEN below:

• Components: Components are used for “dumb” React components unfamiliar with Redux.
• Containers: Containers are used for “smart” React components that are connected to Redux.
• Actions: Actions are used for all the ACTION creators, where the file name should be corresponding to the part of the app.
• Reducers: Reducers are used for all the reducers where the file name is corresponding to the state key.
• Store: Stores are used for store INITIALIZATION. This directory works best in small and mid-level SIZE apps.

Redux Forms PRESENT in React and Redux help in enabling a form in React to use Redux for STORING all of its states. They can be used with raw inputs in HTML5. Redux forms WORK extremely well with User Interface (UI) frameworks, for instance, Material UI, React Widgets, React Bootstrap and many more.

The major FEATURES of Redux forms are as follows:

• Field values persistence through the Redux store.
• Validation (synchronous/asynchronous) and submission.
• Formatting, parsing and normalization of field values.

In order to use connect from React REDUX, we will have to follow a couple of steps to use our store in our container:

• Firstly, we use the mapStateToProps(): This would map the state VARIABLES from our store to the props which we specify.
• Secondly, we connect the above props to our container: The OBJECT returned by the mapStateToProps component is connected to the container.

A sample code for connect from react-redux is GIVEN below:

The key differences between RELAY and Redux are given below:

The workflow features in Redux are as follows:

• RESET: The state of the STORE is allowed to be reset.
• Revert: Revert or Rollback to the last committed state is allowed.
• Sweep: Every disabled action which we have fired unintentionally will be removed.
• Commit: The current state is MADE the INITIAL state.

USING Redux Thunk middleware, we can write action creators returning a function instead of an action. This thunk can postpone the dispatch of an action, or do conditional dispatchment. The arguments passed to the inner function are the store methods dispatch and getState(). In the event of an action creator returning a function, the function gets executed by the Redux Thunk middleware and it does not have to be pure. In other words, the function is allowed to have side EFFECTS, including executing asynchronous API CALLS. It can even dispatch actions. Redux thunk is used to delay the dispatch of an action, or to dispatch in the event of a CERTAIN condition being met. At the time of dispatch of a function instead of an action object, if Redux Thunk middleware is enabled, the middleware will call that function with the dispatch method itself as the first argument.

In ORDER to set the initial state in Redux, we have to pass the initial state as the SECOND argument to createStore as shown below:

An example depicting the usage of a REDUX store is given below:

All the REDUX Store METHODS are as FOLLOWS:

• getState()
• subscribe(LISTENER)
• dispatch(ACTION)
• replaceReducer(nextReducer)

“Store” in Redux is used to carry TOGETHER all the states, REDUCERS, and actions which CREATE the app. Some of the responsibilities of the store are as FOLLOWS:

• The state of the current application from inside is held by the Redux Store.
• We can access the current state using store.getState().
• We can UPDATE the state using store.dispatch(action).
• We can also register listener callbacks using the store.subscriber(listener).

REDUX Saga functions as a separate thread in our programme which is solely responsible for side effects. Redux Saga is a redux middleware. In other words, it means that it can be started, paused, and aborted from the main application using STANDARD Redux actions, has access to the ENTIRE Redux application state, and can ALSO dispatch Redux actions.

The typical data flow in Redux starts with a call back from the User Interface COMPONENT which dispatches an ACTION with a payload. After that, the reducers INTERCEPT and receive the DISPATCHED actions, generating a new application state. After that, the actions are propagated down through a hierarchy of COMPONENTS from the Redux store.