CoITB EXAM 2.

Question 1

CoITB EXAM 2. What is the main purpose of React Testing Library?

• To style React components
• To automate routing
• To test React components from the user’s perspective
• To debug JavaScript syntax

Question 2

How do you prevent the default behavior in an event handler?

• event.preventReact()
• stopDefault()
• event.preventDefault()
• event.preventDefault

Question 3

What does the history object in React Router facilitate?

• Accessing browser history
• Managing component state
• Handling form submissions
• Programmatic navigation

Question 4

What are React components?

• Functions that return React elements
• HTML elements
• Javascript objects
• CSS styles

Question 5

What is a synthetic event in React?

• An event from a browser plugin
• A custom animation handler
• A cross-browser wrapper around the native event
• A manual dispatch tool

Question 6

What does the onClick event handler do in React?

• Updates the DOM directly
• Attaches a CSS class
• Executes a function when a user clicks an element
• Submits a form by default

Question 7

How do you access props inside a functional component?

• Using this.props
• Using props
• Using this.state
• Using state

Question 8

What is the key difference between functional and class components in React?

• Functional components use the this keyword
• Class components use hooks
• Functional components don’t have lifecycle methods
• Class components don’t support props

Question 9

Which is the correct syntax to initialize state using useState()?

• const state = useState(0);
• const [count, setCount] = useState(0);
• setState(count = 0);
• state(count).useState(0);

Question 10

Which of the following is an example of a unit test?

• Testing how multiple components interact with each other
• Testing the full application flow
• Testing if a button component renders with the correct text
• Testing server responses

Question 11

Which object is automatically passed to event handler functions in React?

• nativeEvent
• documentEvent
• windowEvent
• SyntheticEvent

Question 12

How do you pass data from a parent component to a child component?

• Using state
• Using hooks
• Using props
• Using event

Question 13

How do you create a functional component in React?

• Using the class keyword
• Using the extends keyword
• Using the function keyword
• Using the render keyword

Question 14

What does onMouseEnter do in React?

• Triggers when the mouse is clicked
• Triggers when the mouse leaves the element
• Triggers when the mouse hovers over the element
• Triggers when the element is dragged

Question 15

What is the primary purpose of the useEffect hook?

• To manage component state
• To run code after the component renders
• To create global context
• To handle form validation

Question 64 / 87

Which file extension is commonly used for React components?

• .jsx
• .cssx
• .javx

Question 65 / 87

Which of the following is a key best practice when working with React lists?

• Using random values as keys
• Ensuring keys remain inconsistent across renders
• Using array indices as keys for dynamic lists
• Making keys unique among siblings

Question 66 / 87

What is the purpose of the useRef hook in React?

• To subscribe to changes in the component’s props
• To access the DOM node of a component
• To manage component state
• To perform asynchronous operations

Question 67 / 87

What is the correct way to define a route in React Router v6?

• <Route path="/about" to={About} />
• <Route name="/about" element={<About />} />
• <Route path="/about" element={<About />} />
• <Router path="/about" render={<About />} />

Question 68 / 87

What is the purpose of props in React?

• To manage component state
• To handle user events
• To pass data from parent to child components
• To style components

Question 69 / 87

Which feature is unique to styled-components?

• Inline styles
• Scoped component-level styles
• Precompiled CSS files
• Global styles only

Question 70 / 87

What is the purpose of the useMemo hook in React?

• To memoize callback functions
• To manage component state
• To perform data fetching
• To optimize expensive calculations

Question 71 / 87

What is the correct way to define a functional component in React?

• function MyComponent[]
• function MyComponent() { return <div>Hello</div>; }
• component MyComponent() {}
• React.defineComponent('MyComponent')

Question 72 / 87

How do you specify default values for props in a React component?

• By using the defaultProps property
• By using the defaultValues property
• By passing values directly to props
• By using the PropTypes library

Question 73 / 87

Which mechanism allows passing data between routes without exposing it in the URL?

• URL parameters
• Query parameters
• State management libraries
• Local storage

Question 74 / 87

How do you return HTML in a React component?

• Using quotes “HTML here”
• With a return statement containing JSX
• By writing directly inside renderHTML()
• Through a CSS file

Question 75 / 87

What is the purpose of useEffect(() => { … }, [])?

• It runs after every render
• It only runs on mount
• It runs when the component is unmounted
• It prevents rendering

Question 76 / 87

What is the purpose of the export default statement in a React component file?

• To add a CSS file
• To define a stateful component
• To allow the component to be imported elsewhere
• To reset the component

Question 77 / 87

What is the purpose of the useContext hook in React? CoITB EXAM 2.

• To create a new component
• To pass data from child to parent
• To manage global state only
• To avoid prop drilling

State Management

Question 54

What is the difference between controlled and uncontrolled components in React? CoITB EXAM 2.

• Controlled components have their state managed by React, while uncontrolled components manage their state internally
• Controlled components cannot have event handlers, while uncontrolled components can
• Controlled components are faster than uncontrolled components
• Controlled components require fewer resources than uncontrolled components

Question 56

How do you update state in React?

• By directly modifying the state object
• By calling the setState() method
• By using props
• By using the render() method

Lifecycle Methods and Hooks

Question 55

What is the purpose of the shouldComponentUpdate() method in React?

• To update the component’s state
• To handle events
• To control whether a component should re-render
• To perform side effects

Event Handling

Question 57

What technique is used for ensuring the validity of user input in forms?

• Controlled components
• Dynamic rendering
• Form submission handling
• Form validation

Components

Question 58

What does JSX stand for?

• Java Syntax eXtension
• JavaScript and XML
• JavaStyleXHTML
• JavaScript Extension Layer

Styling

Question 59

What is the main idea behind Tailwind CSS?

• Writing inline JavaScript styles
• Applying component-scoped styles
• Using utility classes to build designs without writing custom CSS
• Loading styles dynamically from a CDN

Question 61

Which of the following is a valid Tailwind class for adding padding?

• padding-10
• pad-4
• p-4 CoITB EXAM 2.
• padding-left: 4px

Question 63

Which file extension is used for SASS files? CoITB EXAM 2.

• .sass or .scss
• .style
• .csss
• .jsx

Question 64

Styled-components is an example of which styling pattern?

• CSS Modules
• CSS-in-JS
• SASS
• Tailwind CSS

Rendering Performance

Question 62

How do you optimize performance in React?

• By using memoization techniques
• By minimizing re-renders with PureComponent or React.memo
• By implementing virtualization for large lists
• All of the above

Question 80

What feature of React allows developers to reuse code components?

• Props
• State
• Lifecycle methods
• Virtual DOM