Question 1

How do you conditionally render components in React?

Accepted Answer

Conditional rendering in React can be done with:
- **if statements**: Outside JSX.
- **Ternary operators**: Inside JSX for concise logic.
- **&& operator**: For simple truthy/falsy checks.
- Ensures dynamic UI based on state or props.

Question 2

What are the benefits of using React over vanilla JavaScript?

Accepted Answer

Benefits of React:
- **Component-based**: Reusable, modular UI pieces.
- **Virtual DOM**: Efficient updates for better performance.
- **Ecosystem**: Rich tools and libraries (e.g., Redux, React Router).
- Simplifies state management and UI updates.

Question 3

What is the role of the React Developer Tools?

Accepted Answer

React Developer Tools:
- A browser extension for debugging React apps.
- Allows inspection of component hierarchies, props, and state.
- Includes a Profiler to analyze performance and re-renders.

Question 4

What is the difference between state and props in React?

Accepted Answer

In React:
- **State** is a local, mutable data structure managed within a component. It can change over time via `setState` or `useState`.
- **Props** are immutable data passed from a parent component to a child component.
- State is internal and controlled by the component itself, while props are external and controlled by the parent.

Question 5

What is the difference between class and functional components?

Accepted Answer

In React:
- **Class components**: Use ES6 classes, have lifecycle methods, and local state via `this.state`.
- **Functional components**: Simpler, use Hooks for state and effects, preferred in modern React.
- Functional components are more concise and avoid `this` binding issues.

Question 6

What are the advantages of using React Fragments over divs?

Accepted Answer

React Fragments:
- Avoid adding unnecessary DOM nodes, keeping the structure cleaner.
- Improve performance slightly by reducing DOM operations.
- Maintain JSX syntax without a single parent restriction.

Question 7

What is JSX and how does it work in React?

Accepted Answer

JSX is a syntax extension for JavaScript that looks like HTML:
- It allows writing UI markup within JavaScript code.
- React converts JSX into `React.createElement` calls at runtime.
- Enhances readability and maintainability of component structures.

Question 8

How do you style components in React?

Accepted Answer

Styling in React can be done with:
- **Inline styles**: Using objects in the `style` prop.
- **CSS files**: Imported and applied via class names.
- **CSS-in-JS**: Libraries like `styled-components` or `emotion`.
- Choose based on project size and team preference.

Question 9

What is a React Hook and how do you use useState?

Accepted Answer

Hooks are functions that let you use state and lifecycle features in functional components. `useState`:
- Declares a state variable and a function to update it.
- Returns an array with the current state and the setter.
- Example: Managing a counter in a functional component.

Question 10

What is the difference between controlled and uncontrolled inputs?

Accepted Answer

In React:
- **Controlled inputs**: Value is managed by React state, updated via `onChange`.
- **Uncontrolled inputs**: Value is managed by the DOM, accessed via refs.
- Controlled offers more control, while uncontrolled is simpler for basic forms.

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