Reusable UI components in React

Introduction

Reusable UI components help you build parts of your app once and use them many times. This saves time and keeps your app consistent.

When you want to show the same button style in many places.

When you need a form input that behaves the same everywhere.

When you want to create a card layout that repeats with different content.

When you want to keep your code clean and easy to update.

When you want to share UI parts between different pages or projects.

Syntax

React

function ComponentName(props) {
  return (
    <div>{props.children}</div>
  );
}

// Usage
<ComponentName>Content here</ComponentName>

Use a function that returns JSX to create a component.

Pass data using props to customize the component.

Examples

A simple button component that shows text from the label prop.

React

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

<Button label="Click me" />

A card component that shows a title and any nested content inside.

React

function Card({ title, children }) {
  return (
    <div className="card">
      <h2>{title}</h2>
      <div>{children}</div>
    </div>
  );
}

<Card title="Hello">This is inside the card.</Card>

Sample Program

This app shows two buttons using the same reusable Button component. Each button has its own label and click action. The buttons are accessible with aria-label and keyboard friendly.

React

import React from 'react';

function Button({ label, onClick }) {
  return (
    <button onClick={onClick} aria-label={label}>
      {label}
    </button>
  );
}

export default function App() {
  const handleClick = () => alert('Button clicked!');

  return (
    <main>
      <h1>Reusable Button Example</h1>
      <Button label="Say Hello" onClick={handleClick} />
      <Button label="Say Goodbye" onClick={() => alert('Goodbye!')} />
    </main>
  );
}

Important Notes

Always give components clear names that describe what they do.

Use props to make components flexible and reusable.

Remember to add accessibility features like aria-label for better user experience.

Summary

Reusable components save time and keep your app consistent.

Use props to customize components for different uses.

Make components accessible and easy to use everywhere.

Practice

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

easy

A. They automatically fix bugs

B. They make the app run faster

C. They save time and keep the app consistent

D. They replace the need for CSS styling

Solution

1. Step 1: Understand the purpose of reusable components

   Reusable components are designed to be used multiple times, reducing repeated code.

2. Step 2: Identify the main benefit

   Using reusable components saves development time and keeps the app's look and behavior consistent.

3. Final Answer:

   They save time and keep the app consistent -> Option C

4. Quick Check:

   Reusable components = save time + consistency [OK]

Hint: Reusable means use again to save time and stay consistent [OK]

Common Mistakes:

• Thinking reusable components speed up app runtime
• Believing they fix bugs automatically
• Confusing styling with component reuse

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

easy

A.

B.

C.

D.

Solution

1. Step 1: Recall JSX prop syntax

   Props are passed as attributes with name=value pairs, using quotes for strings.

2. Step 2: Check each option

   uses correct JSX syntax: title="Hello". Others have syntax errors.

3. Final Answer:

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

4. Quick Check:

   Props in JSX use name="value" [OK]

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

Common Mistakes:

• Using curly braces without variable (Option B)
• Adding extra quotes around prop name (Option C)
• Using colon instead of equals (Option A)

3. Given this React component:

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

// Usage:
<Button label="Click me" />

What will be rendered on the page?

medium

A. label

B. Nothing will render

C. {label}

D. Click me

Solution

1. Step 1: Understand prop usage in the component

   The component receives label as a prop and inserts it inside the button element.

2. Step 2: Check the usage

   The component is used with label="Click me", so the button shows "Click me" text.

3. Final Answer:

   <button>Click me</button> -> Option D

4. Quick Check:

   Prop label = "Click me" shown inside button [OK]

Hint: Props passed show as content inside component tags [OK]

Common Mistakes:

• Thinking the literal word 'label' appears
• Confusing JSX expression with string
• Assuming component renders nothing without explicit return

4. What is wrong with this reusable React component code?

function Alert(props) {
  return <div>{message}</div>;
}

// Usage:
<Alert message="Warning!" />

medium

A. The variable 'message' is not defined inside the component

B. The component does not receive props correctly

C. The usage of the component is incorrect

D. The component should return a button instead of a div

Solution

1. Step 1: Check how props are used inside the component

   The component uses {message} but does not extract it from props.

2. Step 2: Identify the error

   Since message is not defined or extracted, this causes a reference error.

3. Final Answer:

   The variable 'message' is not defined inside the component -> Option A

4. Quick Check:

   Props must be accessed via props or destructuring [OK]

Hint: Always get props from function parameter before use [OK]

Common Mistakes:

• Using prop names directly without props or destructuring
• Assuming usage syntax is wrong
• Thinking component must return button

5. You want to create a reusable Input component that can show a label and accept user input. Which approach correctly allows customizing the label text and input placeholder using props?

hard

A. function Input() {
return (
<label>
label
<input placeholder="placeholder" />
</label>
);
}

B. function Input({ label, placeholder }) {
return (
<label>
{label}
<input placeholder={placeholder} />
</label>
);
}

C. function Input(props) {
return (
<label>
props.label
<input placeholder="props.placeholder" />
</label>
);
}

D. function Input({ label, placeholder }) {
return (
<label>
<input placeholder={label} />
{placeholder}
</label>
);
}

Solution

1. Step 1: Check prop usage for label and placeholder

   Props should be destructured and used inside JSX expressions with curly braces.

2. Step 2: Verify correct placement of label and placeholder

   function Input({ label, placeholder }) { return ( <label> {label} <input placeholder={placeholder} /> </label> ); } correctly places label text and uses placeholder prop inside input element.

3. Final Answer:

   function Input({ label, placeholder }) { return ( <label> {label} <input placeholder={placeholder} /> </label> ); } -> Option B

4. Quick Check:

   Destructure props and use inside JSX with curly braces [OK]

Hint: Destructure props and use inside JSX with curly braces [OK]

Common Mistakes:

• Using prop names as plain text instead of expressions
• Putting placeholder text in wrong prop
• Mixing label and placeholder positions