Composition vs inheritance in NextJS - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a simple component using composition in Next.js.

NextJS

function Button({ label }) {
  return <button>{label}</button>;
}

function App() {
  return <div>[1] label="Click me" />;</div>;
}

Drag options to blanks, or click blank then click option'

AButton

BApp

Cbutton

DLabel

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase 'button' instead of the custom component 'Button'.

Trying to use 'App' inside itself causing recursion.

The App component uses composition by including the Button component inside its JSX.

2fill in blank

medium

Complete the code to extend a component using inheritance in React (Next.js).

NextJS

import React from 'react';

class BaseButton extends React.Component {
  render() {
    return <button>{this.props.label}</button>;
  }
}

class [1] extends BaseButton {
  render() {
    return <button style={{ color: 'red' }}>{this.props.label}</button>;
  }
}

Drag options to blanks, or click blank then click option'

AAppButton

BButton

CBaseButton

DRedButton

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same name as the base class causing conflicts.

Not extending the base class properly.

The RedButton class extends BaseButton to change the button style using inheritance.

3fill in blank

hard

Fix the error in the code by completing the blank to correctly use composition with props.

NextJS

function Card({ title, content }) {
  return (
    <div>
      <h2>{title}</h2>
      <p>{content}</p>
    </div>
  );
}

function Page() {
  const info = { title: 'Hello', content: 'Welcome to the page' };
  return <Card [1] />;
}

Drag options to blanks, or click blank then click option'

Ainfo

Binfo.props

C...info

Dprops.info

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the whole object without spreading causes a single prop named 'info'.

Trying to access props incorrectly.

Using the spread operator ...info passes all properties of info as props to Card.

4fill in blank

hard

Fill both blanks to create a component that uses composition and passes a callback prop.

NextJS

function Button({ onClick, label }) {
  return <button onClick=[1]>{label}</button>;
}

function App() {
  function handleClick() {
    alert('Clicked!');
  }
  return <Button onClick=[2] label="Press me" />;
}

Drag options to blanks, or click blank then click option'

AhandleClick

B() => alert('Clicked!')

ChandleClick()

Dalert('Clicked!')

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses calls the function immediately instead of on click.

Passing an inline alert string instead of a function.

The onClick prop should be a function reference, so both blanks use handleClick without calling it.

5fill in blank

hard

Fill all three blanks to create a component that uses inheritance and overrides a method with additional behavior.

NextJS

import React from 'react';

class Logger extends React.Component {
  log() {
    console.log('Logging');
  }
  render() {
    return <div>Logger</div>;
  }
}

class CustomLogger extends Logger {
  [1]() {
    super.[2]();
    console.log([3]);
  }
}

Drag options to blanks, or click blank then click option'

Alog

Brender

C'Custom log message'

D'Overridden log'

Attempts:

3 left

💡 Hint

Common Mistakes

Overriding the wrong method like 'render'.

Not calling the parent method with super.

Logging a variable instead of a string message.

The CustomLogger class overrides the log method, calls the original with super.log(), and adds a custom message.

Practice

1. In Next.js, what is the main advantage of using composition over inheritance when building components?

easy

A. It allows combining small components for better reuse and clarity.

B. It requires less code to extend existing components.

C. It automatically manages component lifecycle methods.

D. It enforces strict type checking at compile time.

Solution

1. Step 1: Understand composition in Next.js

   Composition means building components by combining smaller, reusable parts to create complex UI.

2. Step 2: Compare with inheritance

   Inheritance extends existing components but can lead to complex and less clear code structures.

3. Final Answer:

   It allows combining small components for better reuse and clarity. -> Option A

4. Quick Check:

   Composition = combining parts for clarity [OK]

Hint: Composition combines parts; inheritance extends one component [OK]

Common Mistakes:

• Thinking inheritance is simpler for UI reuse
• Confusing lifecycle management with composition
• Assuming inheritance is preferred in Next.js

2. Which of the following is the correct way to use composition in a Next.js functional component?

easy

A. function Parent() { return <Child>; }

B. function Parent() { return <Child></Child>; }

C. function Parent() { return Child(); }

D. class Parent extends Child {}

Solution

1. Step 1: Identify JSX syntax for composition

   Composition uses JSX tags to include child components inside parent components.

2. Step 2: Check options for correct JSX usage

   function Parent() { return <Child></Child>; } correctly uses <Child></Child> tags, which is valid JSX. function Parent() { return <Child>; } uses opening tag but missing closing tag. class Parent extends Child {} uses inheritance syntax, not composition. function Parent() { return Child(); } calls Child as a function, which is not standard JSX.

3. Final Answer:

   <Child></Child> JSX tags for composition -> Option B

4. Quick Check:

   JSX tags = composition [OK]

Hint: Use JSX tags to compose components, not class inheritance [OK]

Common Mistakes:

• Using class extends syntax for composition
• Calling components as plain functions without JSX
• Missing closing tag for JSX element

3. Given the code below, what will be rendered on the screen?

function Button({ label }) {
  return <button>{label}</button>;
}

function Toolbar() {
  return <div><Button label="Save" /></div>;
}

medium

A. Save

B. Save

C. Toolbar

D. Nothing renders due to syntax error

Solution

1. Step 1: Analyze Button component output

   The Button component returns a button element with the label text inside it.

2. Step 2: Analyze Toolbar component output

   Toolbar renders a div containing the Button component with label "Save", so the button with text "Save" appears inside the div.

3. Final Answer:

   <button>Save</button> -> Option A

4. Quick Check:

   Button label = Save [OK]

Hint: Look inside child component's return for rendered output [OK]

Common Mistakes:

• Confusing parent div content with button content
• Assuming Toolbar text appears inside button
• Thinking syntax error exists due to JSX

4. Identify the error in this Next.js component using inheritance:

class BaseButton extends React.Component {
  render() {
    return <button>Base</button>;
  }
}

function SubmitButton() {
  return <BaseButton label="Submit" />;
}

medium

A. SubmitButton should extend BaseButton instead of being a function.

B. BaseButton cannot be used inside a function component.

C. React.Component cannot be extended in Next.js.

D. BaseButton does not use the label prop in render method.

Solution

1. Step 1: Check BaseButton usage of props

   BaseButton receives a label prop but does not use it in the render method, so label is ignored.

2. Step 2: Check SubmitButton usage

   SubmitButton returns BaseButton with label prop, but since BaseButton ignores label, the button always shows "Base".

3. Final Answer:

   BaseButton does not use the label prop in render method. -> Option D

4. Quick Check:

   Unused prop = bug [OK]

Hint: Check if props passed are actually used in render [OK]

Common Mistakes:

• Thinking functional components can't use class components
• Assuming inheritance is disallowed in Next.js
• Confusing extending with composing

5. You want to create a reusable card component in Next.js that can display different content inside. Which approach best uses composition to achieve this?

function Card({ children }) {
  return <div className="card">{children}</div>;
}

function Profile() {
  return (
    <Card>
      <h2>User Name</h2>
      <p>User details here</p>
    </Card>
  );
}

hard

A. Pass content as a string prop to Card and render inside.

B. Extend Card component with Profile using class inheritance.

C. Use children prop to pass nested components inside Card.

D. Create separate CardProfile component that duplicates Card code.

Solution

1. Step 1: Understand composition with children prop

   The children prop allows passing any nested JSX inside Card, making it reusable for different content.

2. Step 2: Compare other options

   Extending with inheritance is less flexible and not recommended. Passing content as string limits flexibility. Duplicating code reduces reuse.

3. Final Answer:

   Use children prop to pass nested components inside Card. -> Option C

4. Quick Check:

   children prop = composition [OK]

Hint: Use children prop to nest content inside reusable components [OK]

Common Mistakes:

• Trying to extend components with class inheritance
• Passing content as plain strings instead of JSX
• Duplicating component code instead of composing