Most asked questions for react js interview

The React course will teach you how to make your own apps that you can use on your phone, computer, or anywhere else. This article contains often asked react js interview questions, so take a look.

1.What exactly is React?

ANS:Facebook created the React front-end JavaScript library in 2011. It uses a component-based technique to create reusable user interface components. It's used to create complex and interactive online and mobile user interfaces. Despite the fact that it was only open-sourced in 2015, it has one of the largest communities behind it.

2.What distinguishes React from other frameworks?

ANS:The following are some of React's key features: Instead of using the real DOM, it employs the virtual DOM. Server-side rendering is used. It adheres to unidirectional data flow, also known as data binding.

3.In React, why do we need a Router?

ANS:A Router is used to specify many routes, and when a user writes a specific URL, the user is redirected to that route if the URL matches the path of any ‘route' set inside the router. So, we need to add a Router module to our program that allows us to create many routes, each of which leads to a different view.

4.What is the purpose of the switch keyword in React Router v4?

ANS: Although, within the Router, a is used to encapsulate many routes. The switch keyword is used when you just want a single route to be rendered out of the many declared routes. When used, the< switch> tag matches the inputted URL with the defined routes in order. When the first match is detected, the specified route is rendered. As a result, the remaining routes are bypassed.

5.What is React Router and how does it work?

ANS: React Router is a robust routing library built on top of React that makes it easier to add new screens and flows to your project. This maintains the URL up to date with the information on the web page. It's used to create single-page web apps since it has a consistent structure and behavior. React Router offers a straightforward API.

6.What does the term "Store" mean in Redux?

ANS:A store is a JavaScript object that may store the state of an application and provides a few helpful methods for accessing the state, dispatching actions, and registering listeners. An application's whole state/object tree is kept in a single store. As a result, Redux is incredibly straightforward and predictable. We can send middleware to the store to conduct data processing and maintain track of various operations that modify the status of the stores. Reducers are used in all of the activities to return to a new state.

7.Describe the function of Reducer.

ANS:Reducers are pure functions that describe how the state of the application changes in response to an ACTION. Reducers operate by taking the previous state and action and returning to a new state. Based on the type of activity, it calculates what type of update is required and then returns new values. If no work has to be done, it returns to the prior state.

8.What exactly do you mean by "one source of truth"?

ANS: The 'Store' function in Redux is used to store the application's whole state in one place. As a result, all of the component's state is saved in the Store, and they receive changes directly from the Store. The single state tree simplifies debugging and inspecting the application as well as keeping track of changes over time.

9.What exactly is Redux?

ANS:In today's industry, Redux is one of the most popular front-end development libraries. It is a state container for JavaScript applications that are used to handle the whole state of the application. Redux applications are simple to test and may run in a variety of contexts with consistent behavior.

10.Explanation of Flux?

ANS: Flux is an architectural design that enforces data flow in only one way. It uses a central Store, which has authority over all data, to govern derived data and permit communication across numerous components. Any data updates throughout the program must happen just here. Flux improves the application's stability and reduces run-time failures.

11.What are the implications of keys in React?

ANS:Keys are used to distinguishing between different Virtual DOM Elements and the data that drives the UI. They assist React in optimising rendering by recycling all existing DOM elements. These keys must be a unique integer or string, and React will only reorder the items rather than re-rendering them if you use them. As a result, the application's performance improves.

12.Higher Order Components (HOC) are a type of higher order component.

ANS:Higher Order Component is a more sophisticated method of reusing component code. It's essentially a pattern developed from React's compositional nature. HOCs are bespoke components that enclose another component. They can accept any dynamically provided child component, but they will not change or mimic the behaviour of their input components. HOC can be described as 'pure' components.

13.What do you mean when you say "pure components"?

ANS:Pure components are the simplest and most quickly written components. They can be used to replace any component that has merely a render (). These components improve the code's simplicity as well as the application's performance.

14.In React, how are forms created?

ANS:Forms in React are comparable to those in HTML. However, with React, the state is stored in the component's state property and can only be modified using setState (). As a result, the elements can't update their state directly, thus a JavaScript function handles their submission. This function has complete access to the information that a user enters into a form.

15.List some of the situations in which Refs should be used.

ANS:The following are examples of when references should be used: Select text or media playback when you need to manage focus. to start mandatory animations Third-party DOM libraries can be integrated.

16.In React, what are synthetic events?

ANS:Synthetic events are objects that wrap the browser's native event in a cross-browser wrapper. They consolidate the functionality of various browsers into a single API. This is done to ensure that the attributes of the events are uniform across browsers.

17.What are the stages of the lifetime of a React component?

ANS:The lifecycle of a React component is divided into three stages: The component is set to begin its life journey and find its way to the DOM during the initial rendering phase. Phase of updating: After the component is added to the DOM, it can only update and re-render when a prop or state changes. This occurs only at this era. The component is destroyed and deleted from the DOM during the unmounting phase of its life cycle.

18.What is a React state and how does it work?

ANS:React components are built around states. States serve as a data source and should be made as basic as feasible. In a nutshell, states are the objects that determine how components are rendered and behave. They, unlike the props, are malleable and produce dynamic and interactive elements. This is how you get to them. state().

19.In React, what is the objective of render()?

ANS:Render() is required for every React component. It returns a single React element that is the native DOM component's representation. If more than one HTML element needs to be rendered, they must all be included within one enclosing tag, such as form>, group>, div>, and so on. This function must be kept pure, which means it must always return the same result.

20."Everything in React is a component," explain.

ANS:The UI of a React application is made up of components. These components break down the entire user interface into discrete, reusable chunks. Then, without altering the rest of the UI, it renders each of these components independently of one another.

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