Loading... Login Loading... Register

React Basics Quiz

Want to learn more than this quiz offers you? Have a look at my Frontend web development courses.

Create an account and save your quiz results

Login and save your results

First Name *

Last Name *

Email *

Password *

Confirm Password *

I agree to the Terms of Service & Privacy Policy.

Add me to your newsletter.

Question 1/15

How do you create a class-based component in React?

class MyComponent extends React.Component {
  render() {
    return <div>Hello World</div>;
  }
}

Select your answer

By using the 'class' keyword and extending 'React.Component'.

By creating an HTMLElement instance.

By using the 'function' keyword and returning a string.

By using an anonymous function expression.

Question 2/15

Which of these statements about state in React is true?

Select your answer

State is a way to hold dynamic data and can influence the output of a component's render function.

State should be mutated directly for updates.

State is static and does not update once the component is mounted.

State is the same as props.

Question 3/15

What is the purpose of componentDidMount lifecycle method?

Select your answer

To initialize state before rendering.

To update the component state after every render.

To execute code after the component is inserted into the DOM.

To handle event bindings only.

Question 4/15

How can you share logic between two React components?

Select your answer

Through global variable declarations.

By writing CSS selectors.

By creating custom hooks.

By using magic methods.

Question 5/15

What is the purpose of the render() method in class components?

Select your answer

To update the state of the component.

To initialize the component's lifecycle.

To bind event handlers.

To specify the UI elements rendered to the DOM.

Question 6/15

Why is it important to use keys when rendering lists in React?

Select your answer

They allow for the automatic update of state values.

They ensure that list elements are styled correctly.

They enforce security protocols.

They help identify elements to improve performance during re-renders.

Question 7/15

What is the difference between state and props?

Select your answer

State can only hold strings, but props can hold objects.

State is internal and managed within the component, while props are external and passed to the component.

State is a class-based component feature, while props are exclusive to functional components.

State and props serve the same purpose in React.

Question 8/15

What is a React component?

Select your answer

A bundle of functions that performs HTTP requests.

A CSS file that styles the user interface.

An HTML element that is used once in a React application.

A JavaScript function or class that optionally accepts inputs and returns a React element.

Question 9/15

Which statement about 'useState' hook is true?

Select your answer

It lets you add state to function components and returns the current state and a function to update it.

It provides only a state read function and no setters.

It synchronously updates state but does not trigger a re-render.

It is used only in class components.

Question 10/15

What does the constructor method do in a React class component?

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = { count: 0 };
  }

  render() {
    return <div>{this.state.count}</div>;
  }
}

Select your answer

Calls external APIs before rendering.

Renders the HTML content to the page.

Defines the styles for the component.

Initializes the state and binds event handlers.

Question 11/15

What is JSX in React?

Select your answer

A JavaScript library for managing forms.

A syntax extension for JavaScript that looks similar to XML or HTML.

A style sheet language used for describing presentation.

A framework for building REST APIs.

Question 12/15

Which hook in React function components is used to replace componentDidMount?

Select your answer

useState

useReducer

useEffect

useContext

Question 13/15

Which method should be overridden to return a React element from a class component?

Select your answer

componentDidMount()

setState()

render()

getInstance()

Question 14/15

How does React update the user interface efficiently?

Select your answer

By directly manipulating the DOM every time a change occurs.

By sending AJAX requests every few seconds to refresh the page.

By using a virtual DOM to track changes and update only the affected parts of the DOM.

By using a single HTML file that is reloaded every change.

Question 15/15

In React, how do you conditionally render elements based on state?

class Example extends React.Component {
  state = { show: true };

  render() {
    return (
      <div>
        {this.state.show ? <p>Displayed</p> : <p>Hidden</p>}
      </div>
    );
  }
}

Select your answer

JSX does not support conditional rendering.

Use JavaScript conditional operators like '&&' and '?' within JSX.

Create separate HTML files for each condition.

Only use special functions provided by React for conditionals.

Your Results

You did not answer any questions correctly.

Your Answers

Question 1/15

😊 Your answer was correct 🙁 Your answer was incorrect

How do you create a class-based component in React?

class MyComponent extends React.Component {
  render() {
    return <div>Hello World</div>;
  }
}

Available answers

By using the 'class' keyword and extending 'React.Component'.

By creating an HTMLElement instance.

By using the 'function' keyword and returning a string.

By using an anonymous function expression.

To create a class-based component in React, you use the 'class' keyword to define a new class that extends 'React.Component'. This class must include a 'render()' method that returns a React element.

Question 2/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which of these statements about state in React is true?

Available answers

State is a way to hold dynamic data and can influence the output of a component's render function.

State should be mutated directly for updates.

State is static and does not update once the component is mounted.

State is the same as props.

State in React is used to store dynamic data that may change over time and influence the output of a component's render function. Contrary to props, which are passed into a component, state is local to the component and managed entirely within it.

Question 3/15

😊 Your answer was correct 🙁 Your answer was incorrect

What is the purpose of componentDidMount lifecycle method?

Available answers

To initialize state before rendering.

To update the component state after every render.

To execute code after the component is inserted into the DOM.

To handle event bindings only.

The 'componentDidMount' method is invoked immediately after a component is mounted. This is the best place to initiate network requests, set timers, or directly interact with the DOM.

Question 4/15

😊 Your answer was correct 🙁 Your answer was incorrect

How can you share logic between two React components?

Available answers

Through global variable declarations.

By writing CSS selectors.

By creating custom hooks.

By using magic methods.

In React, logic that needs to be shared between components can be encapsulated in custom hooks. These hooks house reusable logic that function components can utilize, promoting cleaner and more maintainable code.

Question 5/15

😊 Your answer was correct 🙁 Your answer was incorrect

What is the purpose of the render() method in class components?

Available answers

To update the state of the component.

To initialize the component's lifecycle.

To bind event handlers.

To specify the UI elements rendered to the DOM.

In class-based React components, the 'render()' method is essential because it specifies what the UI will look like. It returns a React element, which is a description of what you want to see on the screen.

Question 6/15

😊 Your answer was correct 🙁 Your answer was incorrect

Why is it important to use keys when rendering lists in React?

Available answers

They allow for the automatic update of state values.

They ensure that list elements are styled correctly.

They enforce security protocols.

They help identify elements to improve performance during re-renders.

Keys are important in React because they help the library identify elements when updating the UI, producing better performance by reducing re-rendering times. They provide a way to keep elements' stable identities across renders.

Question 7/15

😊 Your answer was correct 🙁 Your answer was incorrect

What is the difference between state and props?

Available answers

State can only hold strings, but props can hold objects.

State is internal and managed within the component, while props are external and passed to the component.

State is a class-based component feature, while props are exclusive to functional components.

State and props serve the same purpose in React.

In React, 'state' is an internal construct maintained by the component itself, used for rendering dynamic data and changes within the component. 'Props', on the other hand, are data passed to the component from a parent for use within the child component.

Question 8/15

😊 Your answer was correct 🙁 Your answer was incorrect

What is a React component?

Available answers

A bundle of functions that performs HTTP requests.

A CSS file that styles the user interface.

An HTML element that is used once in a React application.

A JavaScript function or class that optionally accepts inputs and returns a React element.

In React, a component is a JavaScript function or class that optionally accepts inputs (known as 'props') and returns a React element that describes how a section of the UI should appear. Components can be either stateful or stateless, and they can be composed within other components.

Question 9/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which statement about 'useState' hook is true?

Available answers

It lets you add state to function components and returns the current state and a function to update it.

It provides only a state read function and no setters.

It synchronously updates state but does not trigger a re-render.

It is used only in class components.

The 'useState' hook lets you add state to function components. It returns an array containing the current state and a function to update that state, allowing functional components to manage state without converting them to class components.

Question 10/15

😊 Your answer was correct 🙁 Your answer was incorrect

What does the constructor method do in a React class component?

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = { count: 0 };
  }

  render() {
    return <div>{this.state.count}</div>;
  }
}

Available answers

Calls external APIs before rendering.

Renders the HTML content to the page.

Defines the styles for the component.

Initializes the state and binds event handlers.

In React class components, the 'constructor' method is used for initializing state and, if necessary, binding methods to 'this'. The constructor is called before the component is mounted and is a good place to set up any initial state.

Question 11/15

😊 Your answer was correct 🙁 Your answer was incorrect

What is JSX in React?

Available answers

A JavaScript library for managing forms.

A syntax extension for JavaScript that looks similar to XML or HTML.

A style sheet language used for describing presentation.

A framework for building REST APIs.

JSX is a syntax extension for JavaScript that resembles XML or HTML. It is used within React to describe what the UI should look like. Rather than separating logic and presentation as in some traditional approaches, JSX integrates HTML with JavaScript code, making it easier to visualize the structure of the UI.

Question 12/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which hook in React function components is used to replace componentDidMount?

Available answers

useState

useReducer

useEffect

useContext

In React function components, the 'useEffect' hook can be used to perform side effects similar to the 'componentDidMount' lifecycle method in class components. You can use 'useEffect' to manage tasks like data fetching or directly interacting with the DOM.

Question 13/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which method should be overridden to return a React element from a class component?

Available answers

componentDidMount()

setState()

render()

getInstance()

The

render()

method is required for class components and should be overridden to return the React elements dictating what gets rendered to the DOM. The elements in the

render()

method directly represent the rendered interface.

Question 14/15

😊 Your answer was correct 🙁 Your answer was incorrect

How does React update the user interface efficiently?

Available answers

By directly manipulating the DOM every time a change occurs.

By sending AJAX requests every few seconds to refresh the page.

By using a virtual DOM to track changes and update only the affected parts of the DOM.

By using a single HTML file that is reloaded every change.

React efficiently updates the user interface by using a virtual DOM. When changes occur, React creates a virtual DOM and calculates the differences between the new and previous versions. React then updates only the parts of the real DOM that changed, improving performance and reducing unnecessary updates.

Question 15/15

😊 Your answer was correct 🙁 Your answer was incorrect

In React, how do you conditionally render elements based on state?

class Example extends React.Component {
  state = { show: true };

  render() {
    return (
      <div>
        {this.state.show ? <p>Displayed</p> : <p>Hidden</p>}
      </div>
    );
  }
}

Available answers

JSX does not support conditional rendering.

Use JavaScript conditional operators like '&&' and '?' within JSX.

Create separate HTML files for each condition.

Only use special functions provided by React for conditionals.

In React, you can use JavaScript's built-in conditional operators within JSX to control what gets rendered, such as '&&' for logical AND and '?' for ternary conditions. This enables you to create dynamic interfaces conveniently:

this.state.show ? <p>Displayed</p> : <p>Hidden</p>