React Interview Question PDF By ScholarHat

React Interview Question PDF By ScholarHat

1. Top 50+ React Interview Question & Answers
React Interview Questions and Answers: An Overview
React interview questions and answers is a good way to practice and become a master in
React. also, If you are getting ready for a React developer interview but are a little
nervous about all the questions you could be asked? then you've come to the correct
website! React is
becoming an essential tool for front-end developers. It can be a little challenging to prepare for
a React interview, regardless of experience level. We created this thorough guide of React
interview questions and answers.
In this React Tutorial, we will explore React interview questions and answers, React interview
questions for experienced professionals, and React advanced interview questions.
React Interview Questions and Answers for
Beginners

2. 1. Describe What is React.
Facebook created the front-end JavaScript library React in 2011. It uses a component-based
methodology that facilitates the creation of reusable user interface components. It's used for
the development of intricate and dynamic mobile and online user interfaces.
2. What characteristics does React have?
React's key characteristics are as follows:
3. What are the most important benefits of utilizing React?
Several significant benefits of React include:
Learning and using React is simple.
It supports Server-side rendering.
Since real DOM actions are costly, it will use the virtual DOM (Data Object Model) instead of
the real one.
It adheres to data flow or unidirectional data binding.
To construct the view, it makes use of reusable or composable user interface components.
Read More - React Developer Salary in India

3. React adheres to the MVC design pattern.
React increases efficiency by utilizing Virtual DOM.
It's simple to create dynamic web applications.
React is conducive to SEO.
Reusable components are allowed by React.
In favor of practical tools.
React comes with a large library.
Range of code testing.
Because optimization is done as the code is being translated to JavaScript, it is faster than
standard JavaScript.
Only JavaScript objects can be read by browsers, but JSX isn't just any old JavaScript object.
Therefore, to allow a browser to read JSX, we must first use JSX transformers like Babel to
convert the JSX file into a JavaScript object, which we can then send to the browser.
The following is a list of React's main drawbacks:
It's only a library, React. It is not a comprehensive structure.
Its extensive library requires time to fully comprehend.
The novice programmers could find it challenging to comprehend and write code.
React makes use of JSX and inline templating, which can be challenging and problematic.
It complicates the coding as well.
For JavaScript XML, use JSX. It is a React extension that makes it possible to write JavaScript
code with an HTML-like appearance. It facilitates the understanding of HTML files. The JSX file
strengthens and improves the functionality of the React application. In the same file where you
write JavaScript code, JSX enables you to write XML-like syntax. Preprocessors (i.e.,
transpilers like Babel) subsequently convert these expressions into JavaScript code.
5. Describe JSX.
7. Why is JSX used by us?
6. Why is JSX unreadable by browsers?
4. What are the main drawbacks of React?

4. React uses components that combine both markup and logic, as opposed to dividing the
two technologies into different files.
The majority of the problems can be discovered during compilation, and it is type-safe.
It facilitates the creation of templates.
Virtual DOM operates in three stages:
1. The complete user interface is re-rendered in a virtual DOM representation whenever any
data changes in the React application.
2. Next, the difference between the new DOM and the old DOM representation is evaluated.
3. After the computations are finished, only the modified items are updated in the real DOM.
Initially, a virtual DOM is simply a duplicate of the actual DOM, created with lightweight
JavaScript objects. The elements, their characteristics, and the content as Objects and their
properties are listed in a node tree. React's render function takes its component parts and
turns them into a node tree. After that, it modifies this tree in response to changes made to the
data model by the system or by the user through a variety of activities.
9. Describe how Virtual DOM operates.
8. What does Virtual DOM mean to you?

5. Read More - React Roadmap
Every react component needs to have a render() function. The HTML that should be displayed
in the component is returned by this function. Every element that needs to be rendered must
be contained inside a single parent tag, such as <div> or <form>.
10. What does React's render() method achieve?

6. 12. What Do React Props Mean?
Properties are shortened to props in react. It is a built-in React object that functions similarly to
HTML attributes and stores the value of a tag's attributes. Data transfer between components
is made possible with props. Similar to how arguments are supplied to a function, props are
also passed to the component.
11. How may multiple components be integrated into one?
The following React methods allow you to combine two or more components into one:
JSX Composition
Passing Components as Props
Conditional Rendering
Higher-Order Components (HOCs)
Render Props

7. 13. In React, what is a State?
React components consist of states at their core. Data originates from states, which should be
kept as basic as feasible. In essence, states in react are the objects that control how
components are rendered and behave. Unlike the props, they can be changed to create
dynamic and interactive elements. They can be accessible through this.state().
14. Distinguish in React between States and Props.
The following lists the main distinctions between States and Props.
2
.
3
.
SN Props
1. Props can only be read.
Props cannot be changed.
Props let you transmit arguments, or data,
from one component to another.
State
Asynchronous state modifications are
possible.
A state can change.
The components' information is held by
the state.

8. 4.
5.
6.
7.
8.
The child component has access to props. Child components are not allowed to
access the state.
Components
another through props.
Props may be present in the stateless
component.
communicate with one States can be utilized with the
component to render dynamic changes.
States are incompatible with stateless
components.
Components are reusable thanks to props. The State is not permitted to reuse
components.
The component itself is in charge of the
internal State.
External props are managed by the program
that creates the component.
Using this.setState() function, we can modify a component's State. The State is not always
instantly replaced by this technique.
15. In React, how can the State of a component be updated?

9. Example:
React Interview Questions and Answers for
Intermediate
16. Define the differences between React's stateless and stateful
components.
SN Stateless Components Stateful Components
1. There is no state held or managed by the
stateless components.
The state can be held or managed by the
stateful components.
import React, { Component } from 'react';
class Counter extends Component {
constructor(props) {
super(props);
this.state = {
count: 0,
};
}
incrementCount = () => {
this.setState({ count: this.state.count + 1 });
};
render() {
return (
<div>
<h1>Counter</h1>
<p>Count: {this.state.count}</p>
<button onClick={this.incrementCount}>Increment</button>
</div>
);
}
}
export default Counter;

10. 2.
3.
4.
5.
6.
Knowledge of past, present, and potential
future state changes is absent from it.
It may include information about past,
state
present,
changes.
Another name for it is a class component.
and potential future
Another name for it is a functional
component.
It is clear and easy to comprehend.
Compared to the stateless component, it is
more complex.
It is compatible with any React lifecycle
method.
Reusing the stateful components is
possible.
It is incompatible with all React lifecycle
methods.
Reusing the stateless components is not
possible.
Arrow functions are essentially a condensed form of function expression writing syntax. The
functions are also referred to as "fat arrows" (=>). Due to ES6's default lack of auto-binding,
these functions enable the components' contexts in react to be bound correctly. Most of the
time, arrow functions come in handy when interacting with higher-level functions.
17. What is the purpose of an arrow function in React?

11. 18. What does React define as an event?
Events in React are the responses that are set off by particular actions, such as key presses,
mouse clicks, and mouse hovers. Managing these events is comparable to managing DOM
element events. However, there are some syntactical variations, such as the following:
19. How may an event be created in React?
You may create a React event by carrying out the following example:
20. What do React's synthetic events mean?
The objects that serve as a cross-browser wrapper for the native event of the browser are
known as synthetic events.
They create a single API that combines several browsers' behaviors.
This is done to ensure that the properties displayed by the events are consistent across
various browsers.
1. Events are named in camel case rather than only lowercase.
2. Functions are passed in place of strings when passing events.
import React, { Component } from 'react';
class MyComponent extends Component {
// Event handler function
handleClick = () => {
alert('Button clicked!');
}
render() {
return (
<div>
<h1>React Event Example</h1>
<button onClick={this.handleClick}>Click me</button>
</div>
);
}
}
export default MyComponent;

12. 22. Describe Lists in React.
24. How are React forms created?
23. What use do keys provide in React?
21. How do controlled and uncontrolled components in React vary
from one another?
SN
1.
2.
Controlled
It doesn't hold onto its internal state.
In this case, the parent component
controls the data.
As a prop, it accepts its current value.
Uncontrolled
It keeps its internal state.
In this case, the DOM itself controls the
data.
To get their current values, it uses a ref.
3.
4
.
5
.
Control over validation is possible.
It has more control over the data and
form elements.
Control over validation is not permitted.
Its power over the data and form elements
is restricted.
Data can be shown in an ordered way using lists. Lists in React can be formed similarly to
how they are in JavaScript.
With the help of the map() method, we may go through the list's elements.
HTML forms and React forms are comparable.
However, with React, the state is updated exclusively through setState() and is stored in the
component's state property.
As a result, a JavaScript function manages the elements' submissions and prevents them
from immediately updating their state.
The information that a user enters into a form is fully accessible to this function.
The UI is driven by data that corresponds to distinct Virtual DOM Elements, which are
identified by keys.
By reusing every element already present in the DOM, they assist React in rendering as
efficiently as possible.
These keys have to be distinct strings or numbers, or else React simply rearranges the
elements rather than re-rendering them.
The performance of the application increases as a result.

13. 26. Define the lifecycle methods of React components.
The important React lifecycle methods are:
25. What stages does the lifecycle of a React component go
through?
The life cycle of a React component has the following phases:
getInitialState()
componentWillMount()
componentDidMount()
componentWillReceiveProps()
shouldComponentUpdate()
componentWillUpdate()
componentDidUpdate()
componentWillUnmount()
1. Initial Phase
2. Mounting Phase
3. Updating Phase
4. Unmounting Phase

14. 29. How does React's HOC work?
27. What do React's Pure Components mean?
The simplest and fastest components that can be written are called pure components. Any
component with merely a render() can be swapped out. These elements improve the
application's functionality and code simplicity.
28. What are React's Higher Order Components (HOC)?
React's higher-order components are a sophisticated React method for reusing component
logic.
This function accepts a component as input and outputs a new one. Stated otherwise, this
function takes another function as an input.
The official website states that it is a pattern that results from React's compositional
structure rather than a feature or part of the React API.

15. Elements and components in react differ mostly in the following ways:
HOC can be used for a wide range of tasks, some of which are listed below:
Code Reusability
Props manipulation
State manipulation
Render highjacking
We can write comments in React just like we would in JavaScript. Two possible methods are:
1. Comments in a single line
2. Multiple-line comments
SN
1.
Element
An element is a simple JavaScript object
that specifies the desired characteristics
of the DOM node and component state.
Component
The fundamental building block of a React
application is a component. This class or
function takes an input and outputs a React
element in return.
It has access to the React lifecycle functions
and is capable of holding states and props.
2. It simply contains data about the kind of
component, its attributes, and any child
components that are contained within. It
is unchangeable.
3. It is changeable.
4. On elements, we are unable to use anyWe are able to use techniques on parts.
methods.
31. What is the React commenting process?
32. Why does React need component names to begin with a
capital letter?
30. What distinguishes a React component from an element?
React Interview Questions for Experienced

16. Because fragments do not generate additional DOM nodes, they operate more quickly and
use less memory. Maintaining the intended layout might be challenging with certain CSS
styling, such as CSS Grid and Flexbox, which introduce <div> tags in the middle and have
unique parent-child relationships. There is less clutter in the DOM Inspector.
Props validation is a tool that aids developers in preventing faults and issues in the future.
It improves the readability of your code.
PropTypes is a unique property used by React components that helps you find errors by
verifying the data types of values supplied through props.
You do not have to define components with propTypes in order to use them.
We may use App.propTypes in the React component to apply validation on props.
The JavaScript console will display warnings if any properties are supplied with an invalid
type.
You must set the App.defaultProps after defining the validation rules.
React components that return multiple elements employ fragments. It lets you group a list of
several offspring without expanding the DOM with another node.
Facebook announced the Create React App tool to help developers create React applications.
You can use it to construct React apps that are one page in length. You can avoid time-
consuming setup and configuration tasks like Webpack or Babel by using the preset create-
react app.
The component names in React must begin with a capital letter. The component name will
throw an error as an unrecognized tag if we start it in lowercase. The reason behind this is
that JSX treats tag names in lowercase HTML tags.
36. Describe create-react-app.
33. In React, what are fragments?
35. How can I use React validation on props?
34. Why do fragments work better in React than container divs?

17. 40. How do forms work in React?
38. What exactly are React hooks?
React state and lifecycle aspects can be "hooked into" from a functional component using
hooks, which are functions. Class components are not compatible with React Hooks. They
permitted us to compose parts without a class. Common hooks include useState, useEffect,
and useContext.
37. In React, how do you make a component?
In React, there are two ways to construct a component:
41. How do you interpret the term "props" in React?
39. Which guidelines should you adhere to when using React's
hooks?
When using Hooks in your code, you have to abide by two rules:
Function Components: The easiest method for creating a component in React is this one.
These are the only JavaScript functions that return React elements and take an object
called props as their first parameter.
Class Components: You can define a component using the ES6 class and the class
components function makes it easier.
1. React Hooks can only be invoked at the highest level. Calling them from within loops,
conditions, or nested functions is prohibited.
2. Calling the Hooks is only permitted from React Function Components.
Forms are used by React to facilitate user interaction with web applications.
Users can interact with the program and enter the necessary data whenever needed by
using forms.
Certain elements are present in forms, including radio buttons, checkboxes, buttons, and
text fields.
Numerous functions, including user identification, searching, filtering, indexing, and more,
are accomplished by using forms.

18. Developed on top of React, React Router is a robust routing library that facilitates the
addition of new screens and processes to the application.
By doing this, the URL and the data that is shown on the webpage are kept up to date.
It is used to create single-page web apps and has a consistent structure and behavior.
Callback references are a better solution than the findDOMNode() API.
Because findDOMNode() precludes some future enhancements in React, and callback refs
provide better control when the refs are set and unset.
The abbreviation for References in React is Refs.
This attribute serves to keep a reference to a specific React element or component that the
render configuration function of the component will return.
It is employed to provide pointers to specific elements or components that render() has
returned.
They are useful when we need to add methods to the components or when we need to
measure the DOM.
One feature that is utilized to send a reference from one component to one of its child
components is called ref forwarding.
The React.forwardRef() function can be used to carry it out.
It works very well with higher-order components and is utilized specifically in libraries of
reusable components.
Props are inputs to components in React. They have naming conventions similar to HTML tag
attributes and can be single values or objects holding a set of values supplied to components
upon creation. They are information that a parent component transmits to a child component.
The following component functionality is the primary function of props in React:
Give your component access to custom data.
The status of the trigger changes.
Use via this.props.reactProp within component's render() method.
42. How do refs work in React?
45. What is React Router and how does React require it?
43. What are React's Forward Refs and when are they used?
44. In React, which is the better choice—callback references or
findDOMNode()?

19. It's easy to use React Router's API.
Watch the Video - Learn Routing In React
React routing and conventional routing differ in the following ways:
SN
1.
Conventional Routing
Every view in conventional routing has a
new file in it.
A server receives the HTTP request in
order to deliver the associated HTML
page. In this, the user switches between
various
pages according to each view.
React Routing
There is just one HTML page involved in
React Routing.
2. The only altered attribute is
<BrowserRouter> in the History.
3. The user perceives this as surfing between
pages, but it's merely an illusion.
The unidirectional data flow is enforced by the architectural pattern known as flux. Utilizing a
central store with authority over all data, it facilitates communication between various
The following list includes React Router's key benefits:
It is not required to manually set the browser history in this case.
Link is used to navigate the application's internal links. It is comparable to the anchor
element.
For rendering, the Switch function is used.
There is only one Child element required by the router.
All of the components are listed in <Route> in this.
The three packages that make up the packages are Web, Native, and Core. It supports the
React application's small size.
48. Describe the concept of flux.
46. Describe React Router's benefits.
47. What distinguishes Conventional Routing from React Routing?

20. React application performance can be optimized by the following factors:
Using React's PureComponent or React.memo to avoid unnecessary re-renders.
Implementing lazy loading with React.lazy and Suspense for code splitting.
Using the useCallback and useMemo hooks to memoize functions and values.
Avoiding inline functions and objects as props.
components and manages generated data. Any updates to the data across the application
must happen exclusively here. Flux lowers run-time errors and gives the program stability.
The useEffect is a hook that runs after the render cycle is complete. useEffect can be used to
manage side effects in functional components. While componentDidMount is a lifecycle
method that runs after the initial render in class components. The useEffect can be configured
to run on every render, only on the initial render, or when specific dependencies change.
One of the most popular front-end development libraries available today is Redux. It is utilized
for the overall state management of JavaScript applications and provides a predictable state
container. Redux-developed applications are simple to test and exhibit consistent behavior
across many settings.
One and only source of truth: An object/state tree inside a single store contains the state
of the entire application. It is simpler to debug or inspect the program and to keep track of
changes over time using a single state tree. Read-only status: An action must be triggered
in order to alter the state. A simple JS object that describes the change is called an action.
The action is the minimal representation of a
change to the data, the same as the state is the minimal representation of data.
Modifications are made using pure functions: Pure functions are required to define the
actions' transformation of the state tree. Functions classified as pure have a return value
that is exclusively determined by the values of their inputs.
49. Explain Redux.
51. What is the difference between useEffect and
componentDidMount?
50. What three key principles does Redux adhere to?
52. How can you optimize performance in a React application?

21. Minimizing the use of the global state and keeping components as stateless as possible.
React Portals provide a way to render children into a DOM node that exists outside the
hierarchy of the parent component.
The useReducer hook is used for managing complex state logic in React.
It accepts a reducer function and an initial state and returns the current state and a
dispatch function.
It is similar to Redux but is built into React.
The reducer function specifies how the state should change in response to actions
dispatched by the component.
React Suspense is a feature that allows components to wait for something like data
fetching before rendering.
It provides a way to declare a loading state while the component waits for asynchronous
operations to complete.
It works well with React.lazy for lazy loading components.
Forms in React can be handled using controlled or uncontrolled components.
In controlled components, form data is handled by the component's state, typically using
the useState hook.
In uncontrolled components, data is handled by the DOM itself, usually with refs to access
form values.
It provides a way to share values between components without passing props manually at
every level.
It is used to manage the global state in a React application.
The createContext function creates a context, and Provider and Consumer components are
used to pass and consume the context value, respectively.
54. What is React Suspense?
53. Explain the Context API in React.
56. How do you handle forms in React?
55. How does the useReducer hook work?
57. What are React Portals and how do you use them?

22. They are used for rendering elements like modals, tooltips, or dropdowns that need to
visually break out of the parent container.
You can create a portal using ReactDOM.createPortal(child, containerNode).
useRef is a hook that returns a mutable ref object whose .current property is initialized to
the passed argument.
It persists between renders and can be used to store a reference to a DOM element or any
mutable value. createRef is a method used in class components to create a ref.
It returns a new ref object that can be attached to a DOM element via the ref attribute.
useRef is typically used in functional components, while createRef is used in class
components.
This article provides a detailed overview of React interview questions for all skill levels, from
beginner to advanced. It starts with core ideas like JSX, Virtual DOM, and components before
advancing to more complex subjects like lifecycle methods, hooks, and routing. Each segment
has a series of questions and answers that will provide you with the knowledge and confidence
you need to ace your React interview.We'll also delve into a React Certification Course.
Errors in React components can be handled using error boundaries.
An error boundary is a component that catches JavaScript errors in its child component
tree, logs those errors, and displays a fallback UI.
It is created using a class component with the componentDidCatch lifecycle method and a
getDerivedStateFromError static method.
React.memo is a higher-order component that prevents a functional component from re-
rendering if its props haven't changed.
It is used for performance optimization by memoizing the component and is useful when
you have a component that renders the same output given the same props.
58. How do you handle errors in React components?
59. What is React.memo and when would you use it?
60. Explain the difference between useRef and createRef.
Summary
FAQs

23. Q1. How Can I Prepare for React Interview Questions?
Q2. Where Can I Find Resources for Learning More about React?
To prepare for React interview questions:
You can find resources for learning more about React from the following places:
 . Mock Interviews: Practice with mock interviews to get comfortable with the interview
format and receive feedback on your performance.
7. Review Common Questions: Go through lists of common React interview questions and
answers to understand what to expect and how to articulate your responses.
4. Read Documentation: Regularly read the official React documentation and stay updated
with new features and best practices.
1. Official React Documentation: The official React docs are comprehensive and regularly
updated. React Documentation
5. Study Common Patterns: Familiarize yourself with common design patterns in React, such
as Redux for state management, React Router for navigation, and React Context for passing
data deeply.
 . Practice Coding Problems: Solve coding problems on platforms like LeetCode or
HackerRank to sharpen your algorithmic thinking and problem-solving skills.
1. Understand Fundamentals: Have a strong grasp of JavaScript, ES6+ features, and React
basics like components, JSX, props, state, and lifecycle methods.
3. Practical Experience: Build and deploy several React projects to gain hands-on experience.
This helps in understanding real-world scenarios and problem-solving.
2. Advanced Topics: Learn about hooks (useState, useEffect, useContext, etc.), context API,
higher-order components, and performance optimization techniques like React.memo and
useCallback.

24. Some advanced topics that might be helpful to learn in React include:
2. Context API: Learn how to use Context for state management and to avoid prop drilling.
 . TypeScript: Learn how to integrate TypeScript with React for better type safety and
developer experience.
4. State Management: Explore advanced state management solutions like Redux, MobX, and
Zustand.
7. Testing: Master testing React components using tools like Jest, Enzyme, and React Testing
Library.
1. React Hooks: Deep dive into custom hooks, useReducer, useContext, and optimizing with
useMemo and useCallback.
4. Blogs and Articles: Platforms like Medium, Dev.to, and freeCodeCamp regularly publish
articles on React topics.
2. Online Courses: Websites like Scholarhat, Udemy, Coursera, and Pluralsight offer in-depth
React courses.
3. Server-Side Rendering (SSR): Understand how to implement SSR with frameworks like
Next.js for improved performance and SEO.
3. YouTube Channels: Channels like Traversy Media, Academind, and The Net Ninja have
excellent React tutorials.
5. Books: "The Road to React" by Robin Wieruch and "Learning React" by Alex Banks and Eve
Porcello are highly recommended
5. Performance Optimization: Techniques such as code splitting, lazy loading, memoization,
and avoiding unnecessary re-renders.
Q3. What are Some Advanced Topics That Might Be Helpful to
Learn?

25. 9. GraphQL: Understand how to fetch data with GraphQL and libraries like Apollo Client.
10. Advanced Component Patterns: Higher-order components (HOCs), render props, and
compound components for creating reusable, flexible components.
 . React Suspense and Concurrent Mode: Explore how to handle asynchronous operations
and improve app responsiveness.