Reusable components in React - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a simple reusable button component.

React

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

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

Alabel

Btext

Ccontent

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong prop name like 'text' or 'value' which is not defined.

Forgetting to use curly braces to insert the prop value.

The label prop is used to display the button text inside the button element.

2fill in blank

medium

Complete the code to pass a click handler to the reusable button component.

React

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

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

AonClick

BhandleClick

CclickHandler

DonPress

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different prop name than the one used in the JSX.

Not passing the click handler as a prop.

The component expects a prop named handleClick to be used as the click event handler.

3fill in blank

hard

Fix the error in the reusable component by completing the missing import statement.

React

import React from '[1]';

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

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

Areact-dom

Breact-native

Creact

Dreact-router

Attempts:

3 left

💡 Hint

Common Mistakes

Importing from 'react-dom' which is for rendering, not component definition.

Using 'react-native' which is for mobile apps.

React components need to import from the react package to work properly.

4fill in blank

hard

Fill both blanks to create a reusable component that accepts children and a className prop.

React

function Card({ [1], [2] }) {
  return <div className={className}>{children}</div>;
}

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

Achildren

Bcontent

CclassName

Dstyle

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'content' instead of 'children' for nested elements.

Using 'style' instead of 'className' for CSS classes.

The component uses children to render nested content and className for styling.

5fill in blank

hard

Fill all three blanks to create a reusable list component that maps items to list elements with keys.

React

function List({ items }) {
  return (
    <ul>
      {items.map(([1], [2]) => (
        <li key=[3]>[1]</li>
      ))}
    </ul>
  );
}

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

Aitem

Bindex

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same variable name for both parameters.

Using a variable not defined in the map function as the key.

The map function uses item and index as parameters, and the index is used as the key for each list item.

Practice

1. What is the main benefit of using reusable components in React?

easy

A. They make your app run faster by default

B. They let you write less code and keep your app organized

C. They automatically fix bugs in your code

D. They prevent users from clicking buttons

Solution

1. Step 1: Understand the purpose of reusable components

   Reusable components are designed to be used multiple times to avoid repeating code.

2. Step 2: Identify the main benefit

   Using reusable components helps keep the app organized and reduces the amount of code you write.

3. Final Answer:

   They let you write less code and keep your app organized -> Option B

4. Quick Check:

   Reusable components = less code + organized app [OK]

Hint: Reusable means use again to save code and stay organized [OK]

Common Mistakes:

• Thinking reusable components speed up the app automatically
• Believing they fix bugs without coding
• Confusing reusable components with user interaction controls

2. Which of the following is the correct way to pass a prop named title with value "Hello" to a reusable component Card?

easy

A. <Card title=Hello />

B. <Card title={Hello} />

C. <Card "Hello"=title />

D. <Card title="Hello" />

Solution

1. Step 1: Recall JSX prop syntax

   Props are passed as attributes with name and value inside quotes or curly braces for expressions.

2. Step 2: Check each option

   <Card title="Hello" /> uses correct syntax: title="Hello". <Card title={Hello} /> misses quotes around string. <Card title=Hello /> lacks quotes or braces. <Card "Hello"=title /> has incorrect attribute format.

3. Final Answer:

   <Card title="Hello" /> -> Option D

4. Quick Check:

   Props need name="value" syntax [OK]

Hint: Props look like HTML attributes with quotes [OK]

Common Mistakes:

• Forgetting quotes around string prop values
• Using curly braces without variables
• Swapping prop name and value order

3. What will be the output of this React component usage?

function Greeting(props) {
  return <h1>Hello, {props.name}!</h1>;
}

<Greeting name="Alice" />
<Greeting name="Bob" />

medium

A. Hello, Alice!Hello, Bob!

B. Hello, Alice!

C. Hello, Bob!

D. Error: Cannot render two components like this

Solution

1. Step 1: Understand component usage

   Each <Greeting /> renders an <h1> with the passed name prop.

2. Step 2: Check the two usages

   First renders Hello, Alice!, second renders Hello, Bob!. Both outputs appear in order.

3. Final Answer:

   <h1>Hello, Alice!</h1><h1>Hello, Bob!</h1> -> Option A

4. Quick Check:

   Two components with different props render two greetings [OK]

Hint: Each component instance renders separately with its props [OK]

Common Mistakes:

• Thinking only one component renders
• Believing React errors on multiple components
• Confusing props with state causing wrong output

4. Identify the error in this reusable component code:

function Button(props) {
  return <button>Click {props.label}</button>
}

// Usage
<Button label=Submit />

medium

A. Button component must return a div, not button

B. Props cannot be used inside JSX

C. Missing quotes around the prop value in usage

D. Component name must start with lowercase

Solution

1. Step 1: Check prop usage syntax

   In JSX, string prop values must be in quotes or curly braces.

2. Step 2: Identify the error

   The usage <Button label=Submit /> lacks quotes around "Submit" causing syntax error.

3. Final Answer:

   Missing quotes around the prop value in usage -> Option C

4. Quick Check:

   String props need quotes [OK]

Hint: String props always need quotes in JSX [OK]

Common Mistakes:

• Thinking button must be wrapped in div
• Believing props can't be used inside JSX
• Using lowercase component names

5. You want to create a reusable List component that shows items with a custom renderItem prop function. Which approach correctly uses renderItem inside the component?

hard

A. function List(props) {
return <ul>{
props.items.map(item => <li>{props.renderItem(item)}</li>)
}</ul>;
}

B. function List(props) {
return <ul>{
props.items.map(props.renderItem(item))
}</ul>;
}

C. function List(props) {
return <ul>{
props.renderItem(props.items)
}</ul>;
}

D. function List(props) {
return <ul>{
props.items.forEach(item => props.renderItem(item))
}</ul>;
}

Solution

1. Step 1: Understand how to use renderItem with map

   To render a list, use map to transform each item into JSX, calling renderItem for each.

2. Step 2: Check each option

   function List(props) {
     return <ul>{
       props.items.map(item => <li>{props.renderItem(item)}</li>)
     }</ul>;
   }

   correctly maps items and calls renderItem inside <li>.

   function List(props) {
     return <ul>{
       props.items.map(props.renderItem(item))
     }</ul>;
   }

   calls renderItem incorrectly inside map.

   function List(props) {
     return <ul>{
       props.renderItem(props.items)
     }</ul>;
   }

   calls renderItem once with whole array.

   function List(props) {
     return <ul>{
       props.items.forEach(item => props.renderItem(item))
     }</ul>;
   }

   uses forEach which returns undefined, so no output.

3. Final Answer:

   Option A uses map and renderItem correctly inside list -> Option A

4. Quick Check:

   Use map with renderItem for lists [OK]

Hint: Use map with renderItem inside JSX to render lists [OK]

Common Mistakes:

• Using forEach instead of map for rendering
• Calling renderItem outside map or with wrong argument
• Passing whole array to renderItem instead of single item