Frequently asked React js Interview Questions

Software Development | Design, Digital, Technology | Oct 27,2021 | By Nikita Dhiman

The React course will teach you how to create your own apps that you can use on your phone, PC, or anyplace else. Check out this article for frequently requested react js interview questions.

1.What exactly is Redux?

ANS:Redux is a free and open-source JavaScript library for managing application state. The user interface in React is built with Redux. The Redux application is simple to test and can operate in a variety of contexts while displaying consistent behaviour. Dan Abramov and Andrew Clark were the first to launch it in 2015.

2.What are Redux's three guiding principles?

ANS:The three principles that redux adheres to are as follows: Single source of truth: The whole application's state is saved in an object/state tree within a single Store. The single State tree simplifies the tracking of changes throughout time. It also makes debugging and inspecting the programme easier. The State is read-only: the only method to modify the State is to emit an action, which is an object that describes what happened. This concept ensures that neither views nor network callbacks can write to the State directly. Pure functions are used to make changes: reducers are used to indicate how actions affect the state tree (pure functions). Pure functions accept as parameters the previous State and Action and return a new State.

3.Make a list of Redux's components.

ANS:The Redux components are listed below. STORE: A Store is a location where your application's full State is listed. In Redux, it functions as a brain, overseeing all moving elements. ACTION: An item that describes what occurred. The REDUCER determines how the State will alter.

4.Explain the function of Reducer.

ANS:Reducers read the payloads from the actions and change the Store appropriately through the State. It is a pure function that returns a new state from the starting point. If no work is required, it restores the old State as is.

5.What is the meaning of Store in Redux?

ANS:A Store is an object that stores the application's state and offers methods for accessing it, dispatching Actions, and registering listeners via subscribe (listener). Because the whole State tree of an application is kept in a single Store, Redux is straightforward and predictable. We may provide middleware to the Store to manage data processing and retain a log of different operations that modify the Store's State. Reducers are used by all Actions to return a new state.

6.What are the benefits of Redux?

ANS:The following are the primary benefits of React Redux: The official UI bindings for react applications are React Redux. It is maintained up to date with any API updates to guarantee that your React components behave properly. It promotes good "React" architecture. It performs various speed improvements inside, allowing components to re-render just when necessary. It simplifies code maintenance. Redux's code is written in the form of functions that are minimal, pure, and segregated, making the code testable and independent.

7.Explain the notion of flux.

ANS:Flux is an application architecture used internally by Facebook to construct client-side web applications with React. It isn't a framework or a library. It is a type of architecture that works in tandem with React as a view and adheres to the Unidirectional Data Flow paradigm. It is useful when there is dynamic data in the project and we need to keep the data updated in an efficient manner.

8.What were the main issues with the MVC framework?

ANS:The following are the primary issues with the MVC framework: The cost of DOM modification was too high. It slows down and inefficiently the application. There was a significant amount of memory waste. It makes debugging the application difficult.

9.In what situations do error boundaries fail to detect errors?

ANS:The following are some examples of error boundaries that do not capture errors: Error boundaries do not detect errors that occur within event handlers. During the server-side rendering procedure. When errors are thrown within the error boundary code itself. Callbacks for setTimeout and requestAnimationFrame allow for asynchronous programming.

10.What exactly is an error boundary or set of error boundaries?

ANS:An error boundary is a notion introduced in React version 16. Error boundaries allow you to identify mistakes that occur during the render step. An error boundary is any component that employs one of the following lifecycle mechanisms. Let's look at some of the areas where an error boundary might notice a problem: Phase of rendering Within a lifecycle approach Within the function Object() { [native code] }

11.What exactly are forms in React?

ANS:Forms are used in React to allow users to interact with web apps. The following is a list of the most typical ways forms are used in React: Forms make it easier for users to engage with the application. Users can interface with the programme and enter the necessary information by utilising forms. Forms feature items like as text fields, buttons, checkboxes, radio buttons, and so on that may make the application more interactive and visually appealing. Forms are the most effective approach to collect user input. Forms are used for a variety of activities, including user authentication, searching, filtering, indexing, and so on.

12.What are the guidelines for using hooks in React?

ANS:To utilise hooks in React, we must adhere to the following two rules: Hooks should only be called at the top level of your React methods, not within loops, conditions, or nested functions. This is used to guarantee that hooks are called in the same sequence each time a component renders, as well as to keep hooks in the same state across numerous useState and useEffect calls. Hooks should only be called from React functions. Hooks should not be called from ordinary JavaScript functions.

13.What exactly are hooks in React?

ANS:Hooks are a new feature introduced in React 16.8 that allows us to leverage state and other React capabilities without having to write a class.

14.What exactly are Styled Components?

ANS:Styled-Components is a React library. It is the heir to CSS Modules. It styles React component systems in your application, which is created in a combination of JavaScript and CSS, using boost CSS. It is limited to a single component and cannot spread to other elements on the page.

15.Explain how to style CSS Modules in React.

ANS:CSS Module is a CSS file that is scoped locally by default for all class and animation names. It is only available for the component that imports it, and it cannot be applied to any other Components without your consent. CSS Module files with the.module.css suffix can be created.

16.How many different ways can the React Component be styled?

ANS:React Component can be styled in four ways, which are listed below: Styling in Line Stylesheet in CSS Module for CSS Components with a Style

17.How do you apply styles in React?

ANS:In React apps, we may utilise the style property to apply dynamically calculated styles at render time. Instead of a CSS string, it takes a JavaScript object with camelCased attributes. The style property is compatible with accessing DOM node attributes in JavaScript.

18.Why is the switch keyword present in React Router v4?

ANS:The'switch' keyword is used to select only one of the numerous specified Routes to render. When the path is matched, the Switch> component is utilised to render components only when the path is matched. Otherwise, it returns to the component that was not found.

19.Why do you get the "Router may only have one child element" warning?

ANS:It's because you don't have to enclose your Routes in a Switch or div block that only renders a route.

20.List the benefits of React Router.

ANS:The following are the key benefits of React Router: It is not essential to manually configure the browser history in this case. Link is used to traverse the application's internal links. It is comparable to the anchor tag. It renders using the Switch function. The Router just requires a Single Child element. Every component is specified in Route> in this. The packages are divided into three categories: Web, Native, and Core. It supports the React application's small size.

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