Top 35 Redux Interview Questions And Answers

Question 1

What is Redux DevTools?

Accepted Answer

**Redux DevTools** is a live-editing time travel environment for redux with hot reloading, action replay, and customizable UI. If you don’t want to bother with installing Redux DevTools and integrating it into your project, consider using Redux DevTools Extension for Chrome and Firefox.

Question 2

What is _Flux_?

Accepted Answer

**Flux** is an application design paradigm used as a replacement for the more traditional mvc pattern. It is not a framework or a library but a new kind of architecture that complements React and the concept of Unidirectional Data Flow. Facebook used this pattern internally when working with React The workflow between dispatcher, stores and views components with distinct inputs and outputs as follows:

![](https://github.com/sudheerj/reactjs-interview-questions/raw/master/images/flux.png)

Question 3

Do you need to keepIs all component states in Redux store?

Accepted Answer

You need to keep your application state as small as possible. You don't have to push everything in there. Only do it makes a lot of sense to keep something there Or if it makes your life easier when using Dev Tools. But we shouldn't overload its importance too much.

Question 4

What is _Redux_?

Accepted Answer

**Redux** is a predictable state container for JavaScript apps based on the Flux design pattern. Redux can be used together with ReactJS, or with any other view library. It is tiny (about 2kB) and has no dependencies.

Question 5

What are reducers in redux?

Accepted Answer

The **reducer** is a _pure function_ that takes the previous state and an action, and returns the next state.

```js
(previousState, action) => newState
```

It's called a reducer because it's the type of function you would pass to `Array.prototype.reduce(reducer, ?initialValue)`. It's very important that the reducer stays _pure_. Things you should never do inside a reducer:

* Mutate its arguments;
* Perform side effects like API calls and routing transitions;
* Call non-pure functions, e.g. `Date.now()` or `Math.random()`.

Question 6

How to set initial state in Redux?

Accepted Answer

You need to pass initial state as second argument to `createStore`
```js
const rootReducer = combineReducers({
  todos: todos,
  visibilityFilter: visibilityFilter
});

const initialState = {
  todos: [{id:123, name:'sudheer', completed: false}]
};

const store = createStore(
  rootReducer,
  initialState
);
```

Question 7

What is redux-saga?

Accepted Answer

**redux-saga** is a library that aims to make side effects (i.e. asynchronous things like data fetching and impure things like accessing the browser cache) in React/Redux applications easier and better.
It is available in NPM as

```sh
npm install --save redux-saga
```

Question 8

What is Redux Thunk?

Accepted Answer

**Redux Thunk** middleware allows you to write action creators that return a function instead of an action. The thunk can be used to delay the dispatch of an action, or to dispatch only if a certain condition is met. The inner function receives the store methods dispatch and `getState()` as parameters.

Question 9

What is the difference between React context and React redux?

Accepted Answer

You can use **Context** in your application directly and is going to be great for passing down data to deeply nested components which what it was designed for. Whereas **Redux** is much more powerful and provides a large number of features that the Context Api doesn't provide.

Also, React Redux uses context internally but it doesn’t expose this fact in the public API. So you should feel much safer using context via React Redux than directly because if it changes, the burden of updating the code will be on React Redux instead developer responsibility.

Question 10

What is the difference between _Component_ and _Container_ in Redux?

Accepted Answer

* **Component** is part of the React API. A Component is a class or function that describes part of a React UI.
* **Container** is an informal term for a React component that is connected to a redux store. Containers receive Redux state updates and dispatch actions, and they usually don't render DOM elements; they delegate rendering to presentational child components.

Top 35 Redux Interview Questions

Do you need to keepIs all component states in Redux store?

What is Redux?

What is Redux DevTools?

What is Flux?

What is redux-saga?

What are the core principles of Redux?

What are Redux selectors and Why to use them?

How to structure Redux top level directories?

What are the features of Redux DevTools?

How to add multiple middlewares to Redux?

What is Redux Thunk?

What is the difference between React context and React redux?

How to set initial state in Redux?

What is the difference between Component and Container in Redux?

What are reducers in redux?

What is Redux form?

What is a `store` in Redux?

What are typical middleware choices for handling asynchronous calls in Redux?

What are the differences between redux-saga and redux-thunk?

Are there any similarities between Redux and RxJS?

What is the purpose of the constants in Redux?

How to use connect from react redux?

What are the downsides of Redux over Flux?

How to access redux store outside a react component?

What are the main features of Redux Form?

How to make Ajax request in Redux?

What are the differences between call and put in redux-saga?

Why are Redux state functions called as reducers?

Whats the purpose of at (@) symbol in the redux connect decorator?

What is a Reducer?

How to reset state in redux?

What is the proper way to access Redux store?

What is the mental model of redux-saga?

How Relay is different from Redux?

What is Redux Thunk used for?

Top 35 Redux Interview Questions

Do you need to keepIs all component states in Redux store?

What is Redux?

What is Redux DevTools?

What is Flux?

What is redux-saga?

What are the core principles of Redux?

What are Redux selectors and Why to use them?

How to structure Redux top level directories?

What are the features of Redux DevTools?

How to add multiple middlewares to Redux?

What is Redux Thunk?

What is the difference between React context and React redux?

How to set initial state in Redux?

What is the difference between Component and Container in Redux?

What are reducers in redux?

What is Redux form?

What is a store in Redux?

What are typical middleware choices for handling asynchronous calls in Redux?

What are the differences between redux-saga and redux-thunk?

Are there any similarities between Redux and RxJS?

What is the purpose of the constants in Redux?

How to use connect from react redux?

What are the downsides of Redux over Flux?

How to access redux store outside a react component?

What are the main features of Redux Form?

How to make Ajax request in Redux?

What are the differences between call and put in redux-saga?

Why are Redux state functions called as reducers?

Whats the purpose of at (@) symbol in the redux connect decorator?

What is a Reducer?

How to reset state in redux?

What is the proper way to access Redux store?

What is the mental model of redux-saga?

How Relay is different from Redux?

What is Redux Thunk used for?

What is a `store` in Redux?