React Questions

Abhishek Singh

Score: 🔥 23

Beginner

Took 5 minutes

Programming Framework

React

80%

Questions Attempted

10 / 10

Correct Answers

Incorrect Answers

Points Earned

🔥 8

Question 1

What will happen if you update the state directly in a React component?

The component will re-render, but the state change won't be reflected.
An error will be thrown, and the application will crash.
The component will re-render, and the state change will be reflected correctly.
Nothing will happen; the state will remain unchanged.

Explanation:

Directly updating the state object in React won't notify the component about the change. It's crucial to use setState (in class components) or the state updater function from useState (in functional components) to ensure the change is detected and the component re-renders.

Question 2

In React, what is the primary method for handling events in functional components?

Using inline event handlers like onClick={handleClick}
Defining separate event handler methods within the component
Using the addEventListener method like in vanilla JavaScript
React components don't handle events directly; you must use a library.

Explanation:

Functional components in React handle events directly within the JSX using inline event handlers. You pass a function (often defined within the component) as the value to event attributes like onClick, onChange, etc.

Question 3

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 4

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

Functional components are used for complex UI, while class components are used for simple UI.
Class components can have state and lifecycle methods, while functional components cannot.
Functional components are written in JavaScript, while class components are written in JSX.
There is no difference; both are interchangeable.

Explanation:

The key difference lies in their capabilities: class components can manage state, have lifecycle methods, and inherit features, while functional components focus on rendering UI based on props.

Question 5

Which of the following is a key benefit of using controlled components in React forms?

Direct manipulation of the DOM for improved performance.
Simplified state management with reduced boilerplate code.
Enhanced control over form data and validation.
Seamless integration with external libraries for form handling.

Explanation:

Controlled components excel at providing granular control over form data. By storing data in React's state, you can easily implement validation, dynamic updates, and custom form logic.

Question 6

Which of the following is NOT a valid way to bind an event handler in a React class component?

Binding in the constructor: this.handleClick = this.handleClick.bind(this)
Using an arrow function in the callback: onClick={() => this.handleClick()}
Directly passing the method: onClick={this.handleClick}
Using addEventListener directly on the DOM element

Explanation:

Directly using addEventListener to attach event listeners to DOM elements is not the recommended approach in React. React provides its own event system through Synthetic Events for better control and integration with the virtual DOM.

Question 7

Which of the following JSX expressions is INVALID?

<h1>Hello, {name}!</h1>
<div id={'container'}></div>
<p>2 + 2 = {2 + 2}</p>
<span>This is incorrect {</span>

Explanation:

JSX expressions must be valid JavaScript. You cannot have an opening curly brace '{' without a corresponding closing brace '}' within a JSX expression.

Question 8

What is the primary characteristic of a controlled component in React?

It directly manipulates the DOM to update form values.
It maintains its own internal state for form data.
It relies on the browser to manage form data.
It uses external libraries for form handling.

Explanation:

In React, controlled components store their form data within the component's state. Changes to the form input update the state, and the state updates the input's value, making React the single source of truth.

Question 9

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 10

How can you access the element that triggered an event within a React event handler?

Using this keyword inside the event handler
As a property of the event object (e.g., event.target)
By passing the element as an argument to the event handler
React doesn't provide a way to access the triggering element

Explanation:

The Synthetic Event object provided to React event handlers contains a target property, which references the DOM element that triggered the event.