React.JS Professional Certification

1. Which of the following methods is used to update the state in a React class component?

this.setState()

this.state.update()

setStateDirectly()

updateState()

2. What is the purpose of React's useEffect hook?

To fetch data and perform side effects in function components.

To optimize component performance.

To handle state management.

To manage component styles.

3. Which of the following is true about React keys?

They help identify which items in a list have changed, are added, or are removed.

Keys can be duplicated in the same list.

Keys must be globally unique across the application.

They are only required for stateful components

4. What is JSX in React?

A CSS framework for styling React applications.

A built-in function in React for DOM manipulation.

A JavaScript function for creating components.

A syntax extension for JavaScript that allows writing HTML in React.

5. How can you pass data from a parent component to a child component in React?

Using this.setState in the child component

Using props in the child component.

Using context directly.

Using state in the parent component.

6. Which method in React class components is called after a component is rendered for the first time?

componentDidMount

componentWillMount

componentWillUpdate

shouldComponentUpdate

7. What is the purpose of the React.Fragment component?

To style React components.

To wrap multiple elements without adding an extra DOM node.

To replace the div tag in JSX.

To optimize the performance of React applications.

8. How can you optimize a React component's performance?

Use the useEffect hook for all functions.

Always use inline CSS.

Disable state updates.

Memoize components using React.memo or useMemo.

9. What does the useState hook return?

An object containing the state value and a function to update it.

A function to get the current state value.

A function to reset the state value.

An array with the state value and a function to update it.

10. What is the correct way to handle events in React?

Using inline event handlers with strings.

Directly modifying the DOM with JavaScript.

Using event handlers as functions passed to JSX elements.

Using the on prefix for attribute names, like onClickEvent.

11. What does the useContext hook do in React?

It creates a new React context.

It allows a component to consume a context's value.

It initializes global state for the application.

It fetches data from an API.

12. What is the purpose of PropTypes in React?

To define the types of props that a component expects.

To optimize component rendering.

To create custom hooks.

To set default values for props.

13. What is the primary purpose of React's Virtual DOM?

To directly update the real DOM.

To improve the performance of DOM updates by batching changes.

To store the component's state persistently.

To simplify writing CSS for React components.

14. Which of the following hooks is used to create a reference to a DOM element?

useDOM

useEffect

useRef

useState

15. What does React.StrictMode do?

Enforces stricter linting rules in the project.

Checks for potential issues in components during development.

Enables server-side rendering.

Improves the runtime performance of React applications.

16. What is the correct way to conditionally render a component in React?

Using a ternary operator inside JSX.

Using the renderComponent() method.

Using the display: none CSS property.

Using the if-else statement directly in JSX.

17. Which lifecycle method is used to clean up subscriptions or timers in a React class component?

componentWillUnmount

componentDidMount

shouldComponentUpdate

componentWillUpdate

18. How can you lift state up in React?

By using the useReducer hook.

By passing state from child to parent.

By moving state to the nearest common parent and passing it down as props.

By using context API directly.

19. What is the purpose of React.PureComponent?

It automatically renders components with side effects.

It prevents re-rendering if props and state haven’t changed.

It allows multiple components to share the same state.

It ensures the component is rendered only once.