Reusable components in React - Mini Project: Build & Apply

Building Reusable Components in React

📖 Scenario: You are creating a simple React app that shows different colored buttons. Instead of writing the button code again and again, you want to make a reusable button component that can show different text and colors.

🎯 Goal: Build a reusable React button component called ColorButton that accepts text and color as props and renders a styled button. Then use this component multiple times with different texts and colors.

📋 What You'll Learn

Create a functional React component named ColorButton.

The ColorButton component must accept text and color props.

Use inline styles to set the button's background color using the color prop.

Render three ColorButton components with texts: Save, Cancel, and Delete.

Use colors: green for Save, gray for Cancel, and red for Delete.

💡 Why This Matters

🌍 Real World

Reusable components save time and reduce errors by letting developers write code once and use it many times with different data.

💼 Career

Understanding reusable components is essential for React developers to build scalable and maintainable user interfaces.

1

Create the ColorButton component skeleton

Create a functional React component called ColorButton that accepts props and returns a button element with the text Click me inside.

React

// Your code here

Hint

Start by writing a function named ColorButton that returns a simple button with fixed text.

2

Add props for text and color

Modify the ColorButton component to accept text and color props. Use text as the button's displayed text and set the button's background color style to the color prop.

React

function ColorButton(props) {
  // Use props.text for button text and props.color for background color
  return {props.text};
}

Hint

Use props.text inside the button and set style={{ backgroundColor: props.color }} on the button element.

3

Render three ColorButton components with different props

In the main App component, render three ColorButton components with these exact props: text="Save" and color="green", text="Cancel" and color="gray", and text="Delete" and color="red".

React

function ColorButton(props) {
  return {props.text};
}

function App() {
  return (
    
      {/* Render ColorButton components here with correct props */}
    
  );
}

Hint

Use the ColorButton component three times inside App with the exact props given.

4

Export App component as default

Add the line export default App; at the end of the file to export the App component.

React

function ColorButton(props) {
  return {props.text};
}

function App() {
  return (
    
      
      
      
    
  );
}

// Export App component

Hint

Write export default App; at the end to make the App component usable by React.

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