ReactJS Interview Questions and Answers(New)

Question: What is React?

Answer:

React is an open-source JavaScript library developed by Facebook for building user interfaces, particularly single-page applications (SPAs) where you need a fast, interactive user experience. It enables developers to build large web applications that can update and render efficiently in response to data changes.

Key features of React include:

1. Component-Based Architecture: React applications are built using components, which are reusable and self-contained units of code. Components manage their own state and are combined to create complex user interfaces.

2. Virtual DOM: React uses a virtual DOM to improve performance. When the state of an object changes, React updates the virtual DOM first, compares it with the previous version (using a process called “reconciliation”), and then updates only the changed parts of the actual DOM, minimizing reflows and improving rendering speed.

3. Declarative Syntax: React allows developers to describe what the UI should look like for a given state. React then handles the rendering and updating of the DOM efficiently based on the state changes.

4. JSX (JavaScript XML): JSX is a syntax extension for JavaScript that allows HTML to be written within JavaScript code. This makes it easy to define the structure of the UI directly within JavaScript, making React code more readable and easier to maintain.

5. State and Props:

   • State: Each React component can have its own state, which holds data that may change over time (e.g., user input, API responses).
   • Props: Short for “properties,” props are used to pass data from one component to another, making components dynamic and reusable.

6. One-Way Data Binding: Data flows in React from parent to child components through props, making it easier to track how data changes across the application.

React is widely used for building modern web applications due to its flexibility, performance, and the large ecosystem of tools and libraries around it. It has become a go-to library for developers looking to create interactive UIs with a focus on maintainability and scalability.

Question: What are the key features of React?

Answer:

React has several key features that make it popular for building modern web applications. These features contribute to its efficiency, flexibility, and ease of use in developing interactive UIs. Here are the key features of React:

1. Component-Based Architecture:

   • React applications are built using components, which are small, reusable pieces of code. Each component can be thought of as a building block of the UI.
   • Components can be functional (using hooks) or class-based (older style), and they encapsulate their own state, logic, and rendering.

2. Virtual DOM:

   • React uses a virtual DOM to optimize rendering performance. The virtual DOM is a lightweight copy of the actual DOM.
   • When a component’s state changes, React updates the virtual DOM first, then compares it to the previous version (using a process called reconciliation).
   • It then updates only the parts of the actual DOM that have changed, rather than re-rendering the entire UI, making React faster and more efficient.

3. JSX (JavaScript XML):

   • JSX allows developers to write HTML-like syntax directly within JavaScript code. It makes the code more readable and easier to understand by combining UI structure with logic.
   • JSX is not required, but it is widely used as it simplifies the development process. Under the hood, JSX is converted to JavaScript using tools like Babel.

4. Declarative Syntax:

   • React uses a declarative approach, meaning developers describe what the UI should look like for a given state.
   • React takes care of updating and rendering the UI when the state of the application changes, which simplifies the development process and reduces bugs.

5. One-Way Data Binding:

   • React follows a unidirectional data flow, meaning data is passed from parent to child components via props (properties).
   • This one-way data flow makes it easier to track data changes, debug issues, and understand how components interact with each other.

6. State and Props:

   • State: Each component can have its own internal state, which determines how the component renders and behaves. State can change over time, and React automatically re-renders the component when the state changes.
   • Props: Props are used to pass data from a parent component to a child component. Props are immutable within the child component.

7. React Hooks:

   • Hooks are functions that allow developers to use state and lifecycle features in functional components.
   • Common hooks include:
     • useState: Allows state management in functional components.
     • useEffect: Handles side effects like fetching data or updating the DOM.
     • useContext: Provides access to a component’s context, helping with global state management.

8. Event Handling:

   • React provides an easy and consistent way to handle user interactions (like clicks, keyboard events, etc.) across all browsers.
   • It normalizes events, ensuring they work consistently across platforms.

9. Conditional Rendering:

   • React allows you to render different UI elements based on the state of the application.
   • You can use if-else statements, ternary operators, or logical && operators inside JSX to conditionally render content.

10. React Router:

    • React Router is an external library used to enable client-side routing in React applications.
    • It allows for creating single-page applications (SPAs) with navigation features such as dynamic URL changes without a full page reload.

11. Context API:

    • The Context API allows you to manage global state across the application, avoiding prop drilling (passing props down through multiple layers of components).
    • It’s commonly used for sharing data like user authentication status or theme settings.

12. React Developer Tools:

    • React comes with browser extensions (available for Chrome and Firefox) that provide debugging and inspection tools for React components and state.
    • React DevTools allow you to inspect the component tree, monitor the component state, and optimize performance.

These features make React a powerful and flexible library for building modern, efficient, and interactive web applications. The combination of component-based architecture, the virtual DOM, and declarative UI construction helps streamline the development process and improve application performance.

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