React Questions

Vikas Vimal (Vikki)

Score: 🔥 175

Beginner

Took 8 days

Programming Framework

React

90%

Questions Attempted

10 / 10

Correct Answers

Incorrect Answers

Points Earned

🔥 9

Question 1

In a class component, how do you update the state?

Using this.state = { new state } directly
By calling this.setState({ new state })
Using the useState hook
By modifying this.props object

Explanation:

In React class components, you should never mutate this.state directly. Instead, use this.setState(). This method updates the state and informs React to re-render the component and its children if necessary.

Question 2

In React functional components, how do you typically handle events?

By defining methods inside the component class
Using inline event handlers directly in JSX
By creating separate event listener functions outside the component
Events are not handled in functional components, only in class components

Explanation:

Functional components in React handle events directly within the JSX. You can define functions inline or pass function references as event handlers to JSX elements.

Question 3

How can you access the original DOM event object in a React event handler?

Through the nativeEvent property of the synthetic event object
By directly using event.target or event.currentTarget
React doesn't provide access to the original DOM event; it's completely abstracted.
By using a ref to the DOM element and accessing its event listeners

Explanation:

While the synthetic event object is often sufficient, you can access the underlying native DOM event through event.nativeEvent. This allows interaction with specific DOM APIs if needed.

Question 4

What happens if a prop is not provided to a component with a default prop defined?

An error is thrown
The component will not render
The default prop value is used
The prop will be undefined

Explanation:

Default props act as fallback values when a prop is not explicitly passed to the component.

Question 5

Why is event binding often necessary in class components?

To ensure that this refers to the correct component instance inside event handlers
To prevent default browser behavior for all events
To allow passing custom arguments to event handlers
Event binding is not necessary in React; it's an older JavaScript concept.

Explanation:

In JavaScript, this can be tricky, especially within class methods. Binding event handlers ensures that this refers to the component instance when the handler is executed, allowing access to component methods and properties.

Question 6

What's a common way to bind event handlers in React class components?

Using bind in the constructor
Using arrow functions in the render method
Calling addEventListener within the componentDidMount lifecycle method
Both 'Using bind in the constructor' and 'Using arrow functions in the render method'

Explanation:

Two common approaches to bind event handlers are: 1) using this.handleClick = this.handleClick.bind(this) in the constructor or 2) using arrow functions directly in the render method, which lexically scope this.

Question 7

How can you display validation errors to the user in a React form?

By conditionally rendering error messages based on validation results.
By using browser alerts to notify the user of invalid input.
By logging errors to the console for debugging purposes.
By relying solely on HTML5's built-in validation error messages.

Explanation:

A common approach is to conditionally render error messages in your component's JSX. After validating input, you can update the component's state with error information and use it to control the display of error messages.

Question 8

How do class components in React typically handle events?

By defining methods on the class that act as event handlers
Using inline arrow functions directly in the JSX
Class components cannot handle events; only functional components can
By relying on external state management libraries for event handling

Explanation:

Class components handle events by defining methods that serve as event handlers. These methods are then bound to event attributes in the JSX, usually within the render method.

Question 9

What are props in React?

Internal data of a component
Functions to update the UI
Arguments passed to a component
Lifecycle methods of a component

Explanation:

Props allow data to be passed down from parent components to child components, making them customizable and reusable.

Question 10

What is the second argument of the useEffect Hook used for?

It specifies a list of dependencies that trigger the effect when they change.
It defines the effect to be executed.
It provides access to the previous state and props.
It indicates the effect should be executed only once, like componentDidMount.

Explanation:

The second argument to useEffect is an array of dependencies. If any of these dependencies change between renders, the effect will run again. An empty array ([]) means the effect only runs once, after the initial render.