React Interview Question & Answers PDF By ScholarHat

1. Introduction to React
React is a powerful JavaScript library for building user interfaces, known
for its declarative and component-based approach. It was developed by
Facebook and provides a seamless way to create interactive UIs. With its
virtual DOM and efficient rendering, React has gained popularity among
developers for creating fast and scalable web applications.
One of the key features of React is its reusability and modularity, allowing
developers to build and maintain large-scale applications with ease.
Additionally, React provides robust state management and a rich
ecosystem of tools and libraries, making it a top choice for frontend
development.
byScholarHat

2. WhatisReact?
JavaScriptLibrary
React is a popular JavaScript library for
building user interfaces. It allows developers
to create reusable UI components that
efficiently update and render when the
underlying data changes.
VirtualDOM
One of the key features of React is its virtual
DOM, which enhances performance by
minimizing the need to directly manipulate the
actual DOM. This results in faster rendering
and a better user experience.
Component-Based
React is component-based, meaning UIs are
composed of small, self-contained
components. This makes it easier to manage
complex UIs and encourages reusability,
scalability, and maintainability.
UnidirectionalDataFlow
React follows a unidirectional data flow, which
ensures that any change in the state of the
application triggers a one-way update to the
UI. This makes it easier to understand and
predict how data changes over time.

3. WhyuseReact?
ReusableComponents: React allows developers to create reusable UI
components, which can significantly improve development efficiency
and maintainability. By breaking down the user interface into smaller,
independent components, developers can easily manage and update
various parts of the application.
VirtualDOM: React utilizes a virtual DOM, which enhances the
performance of web applications. The virtual DOM efficiently updates
only the necessary parts of the actual DOM, reducing rendering time
and providing a seamless user experience.
CommunitySupport: React has a large and active community that
continuously contributes to the improvement and expansion of the
ecosystem. This community support ensures that developers have
access to a wide range of resources, libraries, and tools to enhance
their React projects.

4. ReactComponents
React components are the building blocks of any React application. They
are reusable UI elements that can be composed together to create
complex user interfaces. Each component can have its own state,
properties, and lifecycle methods. Components can be either class-based
or functional, allowing developers to choose the appropriate type based on
the specific requirements of the application.
Understanding React components is essential for developing scalable and
maintainable applications. By breaking down the UI into smaller,
independent components, developers can efficiently manage the
application's state and data flow, leading to a more organized and easily
maintainable codebase.

5. WhatareReactcomponents?
BuildingBlocks: React components are the basic building blocks of a React application. They are
reusable, independent, and encapsulated pieces of code that allow you to split the UI into smaller,
manageable parts.
FunctionalComponents: These are simple, lightweight components that are defined as plain
JavaScript functions. They take in props as input and return React elements to render the UI.
ClassComponents: These are more complex components defined using ES6 class syntax. They
have their own state, lifecycle methods, and are used for more advanced use cases.
ReusabilityandComposability: React components promote reusability and composability, allowing
you to create complex UIs by combining smaller components together.

6. Classcomponentsvs. functional
components
ClassComponents
Class components are traditional React
components. They are defined using ES6 classes
and are the original way of writing components in
React. Class components have lifecycle methods,
like componentDidMount and
componentDidUpdate, that allow for more control
over the component's behavior. They are suitable
for complex state management, asynchronous
operations, and using local component state with
this.state. However, class components can be
verbose and require more boilerplate code.
FunctionalComponents
Functional components, also known as stateless
components, are simpler to write compared to
class components. They are defined as plain
JavaScript functions and have no 'this' keyword.
With the introduction of React Hooks, functional
components can now handle state and side
effects, making them a powerful alternative to
class components. Functional components are
more lightweight, easy to read, and test. They
encourage reusability through component
composition and take advantage of JavaScript
ES6 features like arrow functions and
destructuring.

7. StateandProps
In React, state and props are essential concepts for managing and passing
data within components. State is used to store and manage component-
specific data, allowing for dynamic changes to be reflected in the user
interface. It enables components to be interactive and responsive to user
input. Props, short for properties, are used to pass data from a parent
component to a child component. They are read-only and help in
maintaining the integrity of the data flow within the application.
Understanding the nuances of state and props is crucial for building
efficient and maintainable React applications. State is typically managed
within a component, while props are passed down from parent to child
components, forming a hierarchical flow of data. Developers need to
comprehend how to effectively manage state and utilize props to create
reusable and modular components.

8. WhatisstateinReact?
In React, state is a built-in object that allows components to keep track of changes and manage their
dynamic data. It represents the condition of a component at a specific point in time, enabling the
component to create a user interface and respond to user actions. The state can be modified using the
'setState' method, triggering re-rendering of the component and its child components.
State is essential for creating interactive and dynamic user interfaces in React. It holds the data that may
change over time and influences the behavior and output of the components. Understanding how to
effectively manage and update state is fundamental to building robust and responsive React
applications.
Furthermore, state management libraries such as Redux and Context API provide advanced tools for
handling complex state logic and sharing state across multiple components in a scalable manner.
State management in React is a crucial concept for developers to grasp, as it forms the foundation for
creating dynamic and interactive web applications across various domains and industries.

9. WhatarepropsinReact?
Props, short for properties, are a fundamental concept in React that allows data to be passed from a
parent component to a child component. They are used to customize and configure child components,
making them more dynamic and reusable. When a component receives props, it can use that data to
render dynamic content and behavior. Props are read-only, meaning that a child component cannot
modify the props it receives from its parent.
In addition to passing data, props can also be used to pass down event handlers and callback functions
from parent to child components, enabling communication and interaction between different parts of the
application. This makes React components highly composable and flexible, as they can be easily
composed together to build complex UIs.
Understanding how to effectively use and manage props is crucial in React development. It involves
careful consideration of component architecture, data flow, and the separation of concerns. By
leveraging props, developers can create modular, maintainable, and scalable applications.

10. React Interview Questions
1 Explainthepurposeof
componentDidMount() and
componentDidUpdate() lifecycle
methodsinReact.
These lifecycle methods are used to
perform actions after the component has
been mounted and when the component
has been updated due to changes in state
or props. It's important to understand the
differences and use cases for each method.
2 Whatarethedifferencesbetween
controlledanduncontrolled
componentsinReact?
Controlled components are those whose
value is controlled by React state, while
uncontrolled components maintain their
own state internally. Understanding the
pros and cons of each approach is crucial
for building efficient and effective React
applications.
3 HowdoesReactRouterworkand
whatareitsmainfeatures?
React Router is a powerful routing library for
React that enables navigation and routing in
a single-page application. Understanding its
core features, such as nested routing, route
parameters, and programmatic navigation,
is essential for developing complex, multi-
view applications in React.
4 Explaintheconceptof"lifting
stateup" inReactandprovidean
example.
Lifting state up refers to the process of
moving the state from child components to
their parent component in order to share
stateful data and behavior between multiple
components. It's a fundamental concept in
React and plays a key role in creating
scalable and maintainable applications.