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React Basics Quiz

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Question 1/15

When should you use React's StrictMode?

Select your answer

To run the app only in development mode.

To identify potential problems in an application by activating additional checks and warnings.

To enforce strict variable naming conventions.

To restrict the app to use only the 'useState' hook.

Question 2/15

How do you write comments in JSX?

Select your answer

Comments are not allowed in JSX.

Use curly braces and an asterisk: {/* Your comment here */}

Use hashtags like #comment.

For block comments, surround the code with /* comments */.

Question 3/15

What is JSX in React?

Select your answer

A framework for building REST APIs.

A style sheet language used for describing presentation.

A JavaScript library for managing forms.

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

Question 4/15

What is the difference between state and props?

Select your answer

State and props serve the same purpose in React.

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.

Question 5/15

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 6/15

How do you handle events in React?

Select your answer

By defining event handlers in JavaScript and passing them as props to the elements.

By using the 'bind' attribute in HTML.

By writing inline event handlers with HTML attributes such as 'onclick'.

By handling only JavaScript's default events without any React involvement.

Question 7/15

How does React update the user interface efficiently?

Select your answer

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.

By directly manipulating the DOM every time a change occurs.

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

Question 8/15

What is a React component?

Select your answer

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

A CSS file that styles the user interface.

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

A bundle of functions that performs HTTP requests.

Question 9/15

Which statement about 'useState' hook is true?

Select your answer

It is used only in class components.

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

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.

Question 10/15

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.

Question 11/15

How can you bind functions to the correct context in React class components?

Select your answer

By creating new instances inside render.

By declaring them outside the component scope.

By using arrow functions or binding them in the constructor.

By using the 'delay' prop on method calls.

Question 12/15

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

Select your answer

useReducer

useContext

useEffect

useState

Question 13/15

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

State is the same as props.

State should be mutated directly for updates.

Question 14/15

What is a use case for the 'useContext' hook?

Select your answer

To handle complex state management in small applications.

To access the context value without passing props through every level of the component tree.

To replace class components entirely.

To optimize performance by directly modifying the DOM.

Question 15/15

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.

Initializes the state and binds event handlers.

Renders the HTML content to the page.

Defines the styles for the component.

Your Results

You did not answer any questions correctly.

Your Answers

Question 1/15

😊 Your answer was correct 🙁 Your answer was incorrect

When should you use React's StrictMode?

Available answers

To run the app only in development mode.

To identify potential problems in an application by activating additional checks and warnings.

To enforce strict variable naming conventions.

To restrict the app to use only the 'useState' hook.

<React.StrictMode>

is used for highlighting potential problems in a React application. Enclosing the application in

<React.StrictMode>

helps developers identify unsafe lifecycles, legacy API usage, and multiple driver side effects.

Question 2/15

😊 Your answer was correct 🙁 Your answer was incorrect

How do you write comments in JSX?

Available answers

Comments are not allowed in JSX.

Use curly braces and an asterisk: {/* Your comment here */}

Use hashtags like #comment.

For block comments, surround the code with /* comments */.

In JSX, you write comments using curly braces and '/* *'/ syntax. This allows for comments to be embedded within JSX code:

{/* Your comment here */}

. Regular JavaScript comments outside JSX work the same as usual.

Question 3/15

😊 Your answer was correct 🙁 Your answer was incorrect

What is JSX in React?

Available answers

A framework for building REST APIs.

A style sheet language used for describing presentation.

A JavaScript library for managing forms.

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

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 4/15

😊 Your answer was correct 🙁 Your answer was incorrect

What is the difference between state and props?

Available answers

State and props serve the same purpose in React.

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.

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 5/15

😊 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 6/15

😊 Your answer was correct 🙁 Your answer was incorrect

How do you handle events in React?

Available answers

By defining event handlers in JavaScript and passing them as props to the elements.

By using the 'bind' attribute in HTML.

By writing inline event handlers with HTML attributes such as 'onclick'.

By handling only JavaScript's default events without any React involvement.

In React, events are handled using camelCase syntax. Instead of using HTML attributes like 'onclick', you pass a function as the event handler in JSX:

<button onClick={handleClick}>Click Me</button>

Question 7/15

😊 Your answer was correct 🙁 Your answer was incorrect

How does React update the user interface efficiently?

Available answers

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.

By directly manipulating the DOM every time a change occurs.

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

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 8/15

😊 Your answer was correct 🙁 Your answer was incorrect

What is a React component?

Available answers

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

A CSS file that styles the user interface.

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

A bundle of functions that performs HTTP requests.

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 is used only in class components.

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

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.

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

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>

Question 11/15

😊 Your answer was correct 🙁 Your answer was incorrect

How can you bind functions to the correct context in React class components?

Available answers

By creating new instances inside render.

By declaring them outside the component scope.

By using arrow functions or binding them in the constructor.

By using the 'delay' prop on method calls.

In React class components, you can ensure methods have the correct context using arrow functions (since they don't create a 'this' context) or explicitly binding them using the

bind()

method inside the constructor.

Question 12/15

😊 Your answer was correct 🙁 Your answer was incorrect

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

Available answers

useReducer

useContext

useEffect

useState

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

State is the same as props.

State should be mutated directly for updates.

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 14/15

😊 Your answer was correct 🙁 Your answer was incorrect

What is a use case for the 'useContext' hook?

Available answers

To handle complex state management in small applications.

To access the context value without passing props through every level of the component tree.

To replace class components entirely.

To optimize performance by directly modifying the DOM.

The 'useContext' hook provides a way to access values from React's Context API, which is useful for avoiding prop-drilling by passing data through multiple layers of components without needing to pass props explicitly.

Question 15/15

😊 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.

Initializes the state and binds event handlers.

Renders the HTML content to the page.

Defines the styles for the component.

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.