React McQs
Q.1 What will be the output of this code snippet?
class MyComponent extends React.Component {
constructor(props) {
super(props);
this.state = { count: 1 };
} render() {
return
{this.state.count}
; } }
A. 1
B. 0
C. undefined
D. An error message
Q.2 How does React determine whether to re-render a component in response to state changes?
A. It compares the current state with the previous state using a deep comparison
B. It re-renders every time the state changes
C. It uses the shouldComponentUpdate lifecycle method
D. None of the above
Q.3 What is the primary use of the componentDidUpdate method in a class component?
A. To render the initial UI
B. To perform DOM manipulations
C. To update the component in response to prop or state changes
D. To clean up resources
Q.4 In which lifecycle method should you make API calls in a class component?
A. constructor()
B. componentDidMount()
C. render()
D. componentDidUpdate()
Q.5 What is the correct order of lifecycle phases in a React class component?
A. Mounting -> Updating -> Unmounting
B. Updating -> Mounting -> Unmounting
C. Unmounting -> Mounting -> Updating
D. None of the above
Q.6 Which lifecycle method is called right before a component is unmounted from the DOM?
A. componentDidMount()
B. componentDidUpdate()
C. componentWillUnmount()
D. shouldComponentUpdate()
Q.7 What does the setState() function do in a class component?
A. Updates the component’s state and re-renders the component
B. Resets the component to its initial state
C. Deletes the component’s state
D. None of the above
Q.8 What is the issue in this component definition?
function MyComponent(props) { return <h1>{props.title}</h1>; }
A. Missing import statement for React
B.Incorrect props usage
C. Missing return statement
D. No issue
Q.9 Identify the error in this code:
A. Incorrect syntax for prop1
B. Missing props
C. Extra closing tag
D. No error
Q.10 Which of the following is true about React components?
A. They must always be written as ES6 classes
B. They can only return one root element
C. They can return multiple root elements
D. They cannot handle events
Q.11Consider this code snippet:
<div><MyComponent /></div>
What does MyComponent represent here?
A. A parent component
B. A child component
C. A prop
D. A state variable
Q.12 What will the following component render?
A. A string ‘React’
B. A string ‘MyComponent’
C. An error message
D. Nothing
Q.13 What is the primary purpose of props in React?
A. To manage state within the component
B. To pass data and event handlers to child components
C. To enhance the visual styling of components
D. To handle form submissions
Q.14 How are state and props different in React?
A. State is internal and controlled by the component itself, while props are external and controlled by whatever renders the component
B. State and props are the same
C. Props are internal and state is external
D. State can only be used in functional components
Q.15 In React, what is the role of a key prop in a list of elements?
A. It helps React identify which items have changed
B. It defines the unique style for each item
C. It specifies the order of elements
D. It improves the performance of lists
Q.16 Which of the following is a correct way to define a component’s initial state in a class component?
A. Inside the render() method
B. Inside the constructor() method
C. Outside the class definition
D. Directly inside the class body
Q.17 A functional component in React is…
A. A class that extends React.Component
B. A function that returns a React element
C. An HTML element
D. A method inside a class component
Q.18 What are Props in React?
A. Data passed from a parent component to a child component
B. Internal state of a component
C. External libraries used in React
D. Functions inside a component
Q.19 Identify the error in the following JSX: <div>Hello World</div><div>Welcome</div>
A. Missing name attribute
B. Incorrect syntax for value
C. Nothing is wrong
D. Missing closing tag
Q.20 Identify the error in the following JSX: <div>Hello World</div><div>Welcome</div>
A. Missing enclosing tag
B. Syntax error in string
C. Extra closing tag
D. No error
Q.21 What does the following JSX code render?
{‘Hello’ + ‘World’}
A. HelloWorld
B. Hello World
C. ‘Hello’ ‘World’
D. Hello+World
Q.22 What will be displayed on the screen for the following JSX code:
<div>{2 * 5}</div>
A. 2 * 5
B. 10
C. 2 5
D. 25
Q.23 JSX elements must be wrapped in an enclosing tag.
What is this concept known as?
A. Single Child Rule
B. Parent-Child Relationship
C. React Fragment
D. Encapsulation
Q.24 JSX is processed into…
A. JavaScript Objects
B. HTML strings
C. Virtual DOM Nodes
D. Regular DOM Nodes
Q.25 What is the correct syntax for embedding a JavaScript expression in JSX?
A. {expression}
B. expression
C. ${expression}
D. #expression
Q.26 Which of the following is a correct way to comment in JSX?
A. {/* Comment here */}
B. // Comment here
C. <!−− Comment here −−>
D. # Comment here
Q.27 In JSX, how do you express JavaScript variables?
A. Inside curly braces
B. Inside square brackets
C. Inside single quotes
D. Inside parentheses
Q.28 JSX stands for…
A. JavaScript XML
B. Java Syntax Extension
C. JavaScript Syntax
D. Java Structured XML
Q.29 Which feature of React allows it to efficiently update the UI?
A. Real DOM
B. Virtual DOM
C. Shadow DOM
D. Document Fragment
Q.30 What is React primarily used for?
A. Building mobile apps
B. Server-side processing
C. Building user interfaces
D. Data analysis
Q.31 What’s wrong with using indexes as keys in React for the following code?
<ul>{todos.map((todo, index) => <li key={index}>{todo.text}</li>)}</ul>
A. It can cause rendering issues if the list changes
B. It’s not allowed in React
C. It will make the list render slower
D. There’s no issue with this approach
Q.32 Identify the error in this code for rendering a list:
<ul>{todos.map((todo) => <li>{todo.text}</li>)}</ul>
A. Missing key attribute on <li>
B. Incorrect use of map()
C. todo.text is undefined
D. No error
Q.33 What is the correct way to assign a key inside a map() function in React?
A. Use the index of the array
B. Use a unique property of each item
C. Any random number
D. Keys are not necessary in map()
Q.34 How would you render a list of numbers in React?
A. <ul>{numbers.map((number) => <li key={number}>{number}</li>)}</ul>
B. <ul>{numbers.forEach((number) => <li>{number}</li>)}</ul>
C. <ul><li>{numbers.join()}</li></ul>
D. <ul>{for (let number of numbers) {<li>{number}</li>}}</ul>
Q.35 What can happen if you don’t provide unique keys for items in a list in React?
A. The list will not render
B. React will throw an error
C. Performance issues and bugs in the UI update logic
D. The keys will be automatically generated
Q.36 In React, when is it necessary to use keys?
A. When rendering a list of items
B. When rendering a single item
C. When rendering nested components
D. All of the time
Q.37 What type of value should be used for keys in React?
A. Any unique number
B. Any string
C. Any unique identifier
D. Any type of value can be used as a key
Q.38 What is the purpose of keys in React lists?
A. To enhance performance
B. To uniquely identify list items
C. To style list items
D. To handle events on list items
Q.39 What’s wrong with this code snippet for conditional rendering?
{isLoggedIn && || }
A. It will always render
B. It combines two different conditional rendering patterns incorrectly
C. will never render
D. There is no issue; it’s a correct implementation
Q.40 Identify the issue in this conditional rendering code:
{isLoggedIn ? }
A. Missing the false condition
B. isLoggedIn is not defined
C. is not a valid component
D. No issue
Q.41 How does the following code render different components?
{isLoggedIn ? : }
A. Renders if isLoggedIn is true, otherwise
B. Always renders
C. Always renders
D. None of the above
Q.42 What will the following code render?
{isLoggedIn && }
A. if isLoggedIn is true
B. if isLoggedIn is false
C. Nothing
D. An error
Q.43 How can you prevent a component from rendering in React?
A. Return null in the render method
B. Remove the component from the DOM
C. Set the component’s display style to none
D. Uninstall the component
Q.44 What is the purpose of using the ternary operator in React?
A. To perform type checking
B. To create high-order components
C. To render one of two components based on a condition
D. To manipulate state
Q.45 Which operator is commonly used for inline conditional rendering in React?
A. && (Logical AND)
B. || (Logical OR)
C. ? : (Ternary Operator)
D. == (Equality)
Q.46 In React, what is conditional rendering?
A. Rendering components based on certain conditions
B.Rendering components only once
C. Rendering components without using JSX
D. None of the above
Q.47 What is wrong with this event handler definition?
handleClick() { console.log(this.state.value); }
A. ‘this’ is not bound to the component
B. The method doesn’t return anything
C. The method should be static
D. No issue
Q.48 Identify the error in this code:
<button onclick={this.handleClick}>Click me</button>
A. The event handler is not bound in the constructor
B. The event handler attribute should be ‘onClick’, not ‘onclick’
C. The handleClick method does not exist
D. No error
Q.49 What issue might arise from this code snippet?
<button onClick={this.handleClick()}>Click me</button>
A. The handleClick method will be called when the component renders, not when the button is clicked
B. The button will not render
C. The button will render but will not be clickable
D. None of the above
Q.50 How do you pass an argument to an event handler in React?
A. By using an arrow function in the onClick attribute
B. By using the bind method
C. Both a and b
D. None of the above
Q.51 What does the following code do?
<button onClick={this.handleClick}>Click me</button>
A. Renders a button that logs ‘Click me’ when clicked
B. Renders a clickable button that runs the handleClick method when clicked
C. Does nothing
D. Throws an error
Q.52 What is a SyntheticEvent in React?
A. A custom event system for handling native events
B. A simulation of an event for testing
C. A deprecated feature for handling events
D. None of the above
Q.53 Which of the following is true about event handling in React?
A. React events are named using camelCase
B. React event handlers can return false to prevent default behavior
C. React wraps the native event into a SyntheticEvent
D. All of the above
Q.54 Why is it generally a good idea to bind event handler methods in a class component’s constructor?
A. To improve performance
B. To allow access to the ‘this’ keyword
C. To prevent memory leaks
D. To ensure the method is only called once
Q.55 What is the correct way to bind a method to a component instance in a React class component?
A. this.method = this.method.bind(this) in the constructor
B. this.method.bind(this) in the render method
C. Using an arrow function in the method definition
D. All of the above
Q.56 In React, how do you attach an event handler to an element?
A. Using the onEvent attribute
B. Using the addEventListener method
C. Using the handleEvent method
D. None of the above
Q.57 What is wrong with this lifecycle method usage?
componentDidMount() { this.setState({value: this.props.initialValue}); }
A. Props should not be used to set state
B. componentDidMount should not call setState
C. No issue
D. The method is deprecated
Q.58 Identify the issue in this code:
class MyComponent extends React.Component {
render() {
return
{this.state.count}
; } }
A. State is not initialized in the constructor
B. The render method is missing a return statement
C. The JSX syntax is incorrect
D. No issue
Q.59 What is a potential issue with this setState usage?
this.setState({value: this.state.value + 1});
A. It directly mutates the state
B. It may lead to outdated values due to the asynchronous nature of setState
C. It’s the correct way to update state
D. None of the above
Q.60 Consider this code:
componentDidMount() { this.setState({data: ‘new data’}); }.
When is the new data available for render?
A. Immediately after componentDidMount is called
B. After the component re-renders
C. It’s available in componentDidMount
D. None of the above
Q.61 How do you navigate to a different URL using React Router?
A. Using the navigate() function
B. Using the component
C. Using the component
D. All of the above
Q.62 What does the component do in React Router?
A. It switches the application’s theme
B. It provides conditional logic for rendering components
C. It toggles between two routes
D. None of the above
Q.63 Which component in React Router is used to configure a route?
A. <Router>
B. <Route>
C. <Switch>
D. <Link>
Q.64 What is React Router used for in a React application?
A. Managing state within components
B. Routing between different components based on URL
C. Styling components
D. None of the above
Q.65 What’s wrong with using inheritance to extend a React component like this:
class EnhancedComponent extends BaseComponent { /…/ }?
A. React does not support class inheritance
B. Inheritance can lead to a more complex and less predictable component structure
C. BaseComponent methods can’t be overridden
D. There is no issue
Q.66 Identify the error in this composition approach:
where does not render this.props.children.
A. The should not be nested inside
B. The component needs to render this.props.children
C. There is no error in this approach
D. The components should be connected using inheritance
Q.67 What is a higher-order component (HOC) in React, and how does it relate to composition?
A. A component that inherits from another component
B. A function that takes a component and returns a new component
C. A class that renders multiple components
D. None of the above
Q.68 How can you use composition to pass content into a component in React?
A. By using a prop to pass a function
B. By passing content as a child between component tags
C. By extending the component class
D. By using React context
Q.69 Which React code snippet demonstrates composition?
A. <Parent><Child /></Parent>
B. class Parent extends React.Component { /*…*/ }
C. <Parent>{this.props.children}</Parent>
D. React.cloneElement(this.props.children)
Q.70 Why might you choose composition over inheritance when designing React components?
A. Inheritance is not supported in React
B. Composition allows for easier code refactoring and maintenance
C. Composition makes components more complex
D. None of the above
Q.71 What is an example of composition in React?
A. Extending one component from another
B. Using state and lifecycle methods in class components
C. Passing components as props to other components
D. Using context API
Q.72 How does React achieve code reuse with composition?
A. By inheriting methods from parent components
B. By rendering props children
C. By using higher-order components
D. By using React hooks
Q.73 What is a key advantage of composition over inheritance in React?
A. Composition allows you to use multiple inheritances
B. Composition provides a clearer component hierarchy
C. Composition is easier to debug
D. Inheritance is more performant
Q.74 In React, what is favored for reusing component logic?
A. Inheritance
B. Composition
C. Both equally
D. Neither
Q.75 What’s the issue with this lifted state approach?
class Parent extends React.Component {
constructor(props) {
super(props);
this.state = { value: ” };
} render() {
return <Child value={this.state.value} onChange={value => this.setState({value})} />; } }
A. onChange handler in Child is not implemented correctly
B. The value prop in Child is redundant
C. setState should not be used in the render method
D. No issue
Q.76 Identify the problem in this code:
class Parent extends React.Component { updateState() { /…/ } render() { return ; } }
A. updateState should be bound to this in the constructor
B. updateState is missing parameters
C. Child component should not receive onChange prop
D. No issue
Q.77 What is the correct way to update the parent’s state from a child component?
A. Directly modify the parent’s state
B. Use a callback function provided by the parent
C. Send a request to the parent via an event bus
D. None of the above
Q.78 How do you lift state up from a child component to a parent component?
A. By using global state management libraries like Redux
B. By passing a state setter function from parent to child
C. By using React context
D. None of the above
Q.79 What is a potential downside of lifting state up in a large React application?
A. Increased rendering time for all components
B. Difficulty in managing state across distant components
C. Increased risk of security vulnerabilities
D. None of the above
Q.80 In the context of lifting state up, what is a common pattern for two-way data binding between parent and child components?
A. Using refs to update parent state from the child
B. Using a callback function passed from parent to child
C. Relying on global variables
D. None of the above
Q.81 Why is lifting state up beneficial in React applications?
A. It enhances the performance of the application
B. It allows child components to modify each other’s state directly
C. It enables multiple components to share and synchronize state changes
D. It simplifies the debugging process
Q.82 What does “lifting state up” mean in React?
A. Moving state to a child component for shared access
B. Moving state to a parent component for shared access
C. Deleting state
D. None of the above
Q.83 What’s wrong with this form submission handling?
<form onSubmit={this.handleSubmit}> <input type=”submit” value=”Submit” /> </form>
A. onSubmit should be onsubmit
B. The form should have an action attribute
C. The form is missing an onChange handler for the input
D. No issue
Q.84 Identify the mistake in this form input:
<input type=”text” value={this.state.value} onchange={this.handleChange} />
A. The value attribute is incorrect
B. The type attribute is incorrect
C. The onchange event handler should be onChange
D. No mistake
Q.85 What is the correct way to handle a form input change in React?
A. onChange={(event) => this.setState({value: event.target.value})}
B. onInput={(event) => this.setState({value: event.target.value})}
C. onChange={this.updateValue}
D. onInputChange={(event) => this.setState({value: event})}
Q.86 How would you create a basic text input field in a React component?
A. <input type=”text” value={this.state.value} />
B. <input type=”text” />
C. <textfield value={this.state.value} />
D. <textinput value={this.state.value} />
Q.87 What is the main difference between controlled and uncontrolled components in React?
A. Controlled components do not use state, while uncontrolled components do
B. Controlled components use refs, while uncontrolled components do not
C. Controlled components manage their own state, while uncontrolled components store their state in the DOM
D. None of the above
Q.88 How do you collect form input values in React?
A. Using refs to directly access the DOM element
B. By storing the values in the state on every change
C. Using document.getElementById()
D. None of the above
Q.89 In React, how do you handle form submission?
A. Using a submit button outside the form
B. By manually updating the DOM
C. Using an onSubmit event handler in the form element
D. None of the above
Q.90 What is a controlled component in React?
A. A component that controls all the forms in the app
B. A component whose state is controlled by React
C. A component that cannot be modified
D. None of the above
Q.91 What is the correct way to pass additional arguments to a Higher-Order Component in React?
A. HOC(Component, additionalArg)
B. <HOC component={Component} additionalArg={additionalArg} />
C. HOC(additionalArg)(Component)
D. HOC.bind(null, additionalArg)(Component)
Q.92 How do you apply a Higher-Order Component to a React component?
A. <HOC><Component /></HOC>
B. HOC(Component)
C. <Component hoc={HOC} />
D. HOC.apply(Component)
Q.93 What is a key consideration when using Higher-Order Components?
A. They should be used for managing state
B. They should not alter the component’s signature
C. They are the only way to share logic between components
D. None of the above
Q.94 Why are Higher-Order Components useful in React?
A. They make components more reusable
B. They allow components to inherit from multiple sources
C. They increase the performance of components
D. None of the above
Q.95 What is a Higher-Order Component (HOC) in React?
A. A component that renders other components
B. A component that is rendered by other components
C. A function that takes a component and returns a new component
D. None of the above
Q.96 How do you address a performance issue caused by unnecessary re-renders in components consuming a frequently updated context?
A. Using the shouldComponentUpdate lifecycle method
B. Using the React.memo higher-order component
C. Splitting the context into multiple smaller contexts
D. All of the above
Q.97 What might be the issue if a component is not receiving the expected context value?
A. The component is not wrapped with the Context.Provider
B. The context value is not updated correctly
C. Both of the above
D. None of the above
Q.98 How can you dynamically change the value of a context in a component tree?
A. By modifying the context object directly
B. By updating the state that’s passed to the context provider’s value prop
C. By using a reducer with the context
D. None of the above
Q.99 How do you consume a context value in a functional component?
A. Using Context.Consumer
B. Using the useContext hook
C. Using this.context
D. None of the above
Q.100 What is a potential drawback of using the Context API excessively?
A. Increased memory usage
B. Difficulty in managing and tracking state changes
C. Slower component re-renders
D. All of the above
Q.101 How does the Context API help in avoiding “prop drilling”?
A. By using global variables accessible by all components
B. By allowing components to subscribe to context changes directly
C. By automatically passing props to all child components
D. None of the above
Q.102 What is the primary use of the Context API in React?
A. To manage global state across the entire application
B. To enhance performance
C. To handle form validations
D. To create high-order components
Q.103 How do you prevent a memory leak in a component that subscribes to an external data source using useEffect?
A. By unsubscribing from the data source in the return function of useEffect
B. By using the useMemo hook
C. By reducing the number of re-renders
D. None of the above
Q.104 What could cause an infinite loop in a component using useEffect?
A. Omitting the dependency array
B. Including a state variable that constantly changes within the dependency array
C. Both of the above
D. None of the above
Q.105 Identify the issue in this useState usage:
const [count, setCount] = useState(0); setCount(count + 1);
A. The state update should be inside a component or effect
B. The initial state is incorrectly set
C. The setCount function is used incorrectly
D. No issue
Q.106 How can you implement a fetch request with useEffect that updates the state when the data is retrieved?
A. By putting the fetch request inside the useEffect hook and updating the state in the .then() callback
B. By using async/await inside the useEffect hook
C. By creating a separate async function outside of useEffect and calling it inside useEffect
D. All of the above
Q.107 What is the correct way to update state based on the previous state using useState?
A. setState(prevState => prevState + 1)
B. setState(state + 1)
C. setState(prevState => { return prevState + 1; })
D. setState({ …state, count: state.count + 1 })
Q.108 How do you initialize state with the useState hook?
A. useState(initialState)
B. useState()
C. useState({})
D. useState(() => initialState)
Q.109 How do custom hooks enhance the functionality of React components?
A. By adding new features to React that are not available in built-in hooks
B. By allowing state and lifecycle features to be reused across multiple components
C. By replacing the need for class components
D. None of the above
Q.110 What does the useCallback hook do?
A. Memoizes a callback function to prevent unnecessary re-renders
B. Creates a new function every time the component renders
C. Runs a function in the background
D. None of the above
Q.111 What is the correct way to conditionally run an effect with the useEffect hook?
A. By using an if statement inside the useEffect hook
B. By setting a specific condition in the dependency array
C. By using a ternary operator inside the useEffect hook
D. None of the above
Q.112 What does the useEffect hook replace in class components?
A. componentDidMount and componentDidUpdate methods
B. componentDidMount, componentDidUpdate, and componentWillUnmount methods
C. componentWillUnmount method
D. None of the above
Q.113 When is the useEffect hook run in a React component?
A. After every render of the component, including the first render
B. Only when the component mounts
C. Only when the component updates
D. None of the above
Q.114 What is the purpose of the useState hook in React?
A. To connect a React component to an external state management library
B. To manage state in a class component
C. To manage local state in a functional component
D. To store global state across the application
Q.115 What might cause a not to render the expected component in React Router?
A. The is outside a
B. The corresponding for “/about” is not defined
C. Both of the above
D. None of the above
Q.116 Identify the issue with this route definition:
in a React Router application.
A. No issue
B. The route should have an exact prop
C. The component should be defined inline
D. The path should be more specific
Q.117 What is the use of the exact prop in a component?
A. To exactly match the component’s CSS class
B. To ensure that the route only matches the exact path without any sub-routes
C. To make the component render only once
D. None of the above
Q.118 How can you programmatically navigate to a new route in React Router?
A. Using this.props.history.push(‘/new-route’)
B. Using navigate(‘/new-route’)
C. Using this.context.router.push(‘/new-route’)
D. None of the above
Q.119 How do you define a route parameter in React Router?
A. <Route path=”/:id” />
B. <Route path=”{id}” />
C. <Route path=”/(id)” />
D. <Route path=”/id” />
Q.120 What is the difference between the and components in React Router?
A. is used for external links while is for internal navigation
B. has styling options for active links
C. There is no difference
D. None of the above
Q.121 How do you identify and resolve issues related to event handling in tests using React Testing Library?
A. By ensuring the correct event types and payloads are used
B. By manually triggering events in the component
C. Both A and B
D. None of the above
Q.122 What common issue should you be aware of when testing asynchronous behavior in React components?
A. Tests completing before asynchronous operations
B. Ignoring error handling in asynchronous operations
C. Both A and B
D. None of the above
Q.123 How do you test a component that fetches data from an API using React Testing Library?
A. By making real API calls during the test
B. By mocking the fetch function and simulating a response
C. By testing only the loading state
D. None of the above
Q.124 How do you mock a module or function in Jest?
A. Using jest.fn() to create a mock function
B. Using jest.mock() to mock an entire module
C. Both A and B
D. None of the above
Q.125 What is a best practice when writing tests for React components using React Testing Library?
A. To frequently use snapshot testing for component output
B. To test internal component states and methods
C. To focus on testing the component as users would interact with it
D. To mock all component props and external modules
Q.126 How does React Testing Library differ from enzyme in testing React components?
A. React Testing Library focuses on internal component state and methods, while enzyme focuses on rendering components
B. React Testing Library focuses on rendering components and user interactions, while enzyme focuses on internal component state and methods
C. React Testing Library is only for functional components, while enzyme is for both functional and class components
D. None of the above
Q.127 What is the main purpose of using Jest in React applications?
A. For end-to-end testing
B. For performance testing
C. For unit and integration testing
D. For style testing
Q.128 How can you troubleshoot TypeScript errors related to the context API in a React application?
A. By ensuring the context value matches the type defined in the Context creation
B. By using any type for all context values
C. By avoiding the use of context in TypeScript applications
D. None of the above
Q.129 What is a common issue when using TypeScript with React and how can it be resolved?
A. Type errors due to incorrect prop types, resolved by ensuring prop types match the expected interface or type
B. Difficulty in setting up the TypeScript environment, resolved by configuring the TypeScript compiler
C. Both A and B
D. None of the above
Q.130 How do you type a React component with generic props in TypeScript?
A. By using the React.ComponentType with generics
B. By defining a generic interface for props and using it in the component
C. By using the React.FC type with a generic parameter
D. Both A and C
Q.131 How do you define state in a TypeScript class component?
A. state: StateType = initialState; inside the class
B. this.state = { … } inside the constructor
C. Both A and B
D. None of the above
Q.132 In TypeScript, how can you define the types of props in a React functional component?
A. Using type assertions
B. Using interfaces or types to define the shape of props
C. Using generic types
D. Both B and C
Q.133 How does TypeScript enhance the development of large-scale React applications?
A. By reducing the size of the final bundle
B. By providing better integration with third-party libraries
C. By offering enhanced readability and maintainability through type annotations and interfaces
D. By increasing rendering speed
Q.134 What is the primary benefit of using TypeScript with React?
A. Improved runtime performance
B. Automatic type conversion
C. Static type checking and easier error detection
D. None of the above
Q.135 What can cause a memory leak in a React component, and how do you fix it?
A. Not cleaning up event listeners or subscriptions in useEffect
B. Using outdated libraries
C. Incorrect use of state
D. Both A and B
Q.136 How do you identify and address unnecessary re-renders in a React application?
A. Using the React DevTools Profiler
B. Using console logs in the render method
C. Reviewing the code for inefficient patterns
D. All of the above
Q.137 In what scenario is using shouldComponentUpdate or React.memo not effective for preventing unnecessary re-renders?
A. When the component always receives new object references as props
B. When the component is stateless
C. When the component has no children
D. None of the above
Q.138 How can you implement lazy loading of components in React?
A. Using React.lazy and Suspense
B. Using the lazy function in JavaScript
C. Deferring the component rendering with setTimeout
D. None of the above
Q.139 What is the main benefit of code splitting in React?
A. To reduce the initial loading time of the application
B. To simplify the development process
C. To improve the runtime performance
D. None of the above
Q.140 How does the useCallback hook contribute to performance optimization in React components?
A. By caching functions to prevent unnecessary re-creations
B. By reducing the bundle size
C. By accelerating the rendering process
D. None of the above
Q.141 What is the purpose of using React.memo in a functional component?
A. To memorize the component’s state
B. To prevent a component from re-rendering unless its props have changed
C. To cache the component’s output
D. None of the above
Q.142 How do you troubleshoot a memory leak in a component caused by a custom hook?
A. By ensuring cleanup functions are defined in effects
B. By reducing the number of state variables
C. By avoiding the use of state and effects altogether
D. None of the above
Q.143 What is a common mistake to avoid when using custom hooks?
A. Using them inside conditional statements
B. Defining them inside components
C. Calling them outside of functional components
D. All of the above
Q.144 How can you optimize performance in a component that uses many custom hooks?
A. By using the useCallback and useMemo hooks
B. By using React.PureComponent
C. By minimizing the number of state updates
D. Both A and C
Q.145 How do you create a custom hook in React?
A. By adding a new method to the React object
B. By creating a function that starts with use and uses other hooks
C. By extending the React.Component class
D. None of the above
Q.146 What should you consider when creating a custom hook?
A. Its impact on the component’s lifecycle
B. The types of components it will be used in
C. How it manages state and side effects
D. All of the above
Q.147 What are the benefits of using advanced hooks like useReducer and useContext together?
A. They allow for global state management without third-party libraries
B. They simplify the process of prop drilling
C. They provide a more performant solution to state management
D. Both A and B
Q.148 What is the main purpose of custom hooks in React?
A. To interact with the DOM directly
B. To create more complex components
C. To reuse stateful logic between different components
D. To enhance performance
Q.149 How do you avoid namespace clashes in props when using multiple Higher-Order Components?
A. By using unique prop names across all HOCs
B. By nesting HOCs instead of composing them
C. By using React’s built-in prop namespace feature
D. None of the above
Q.150 What could cause a React component wrapped in an HOC not to update as expected?
A. The HOC does not pass down props to the wrapped component
B. The wrapped component is not exporting correctly
C. The HOC is not connected to the Redux store
D. None of the above
