What is a component in React - Hands-On Activity

What is a component

📖 Scenario: You want to build a simple webpage that shows a greeting message. To do this, you will create a React component that displays the message.

🎯 Goal: Build a React functional component called Greeting that shows the text "Hello, friend!" on the page.

📋 What You'll Learn

Create a React functional component named Greeting

Inside the component, return a <div> element

The <div> should contain the exact text: "Hello, friend!"

Export the Greeting component as default

💡 Why This Matters

🌍 Real World

React components let developers build web pages by combining small, reusable pieces. This makes building and maintaining websites easier.

💼 Career

Understanding components is essential for React developers, a popular skill in web development jobs.

1

Create the React functional component

Write a React functional component named Greeting that returns a <div> element.

React

# Your code here

Hint

Start by writing function Greeting() { return <div></div>; } and export it.

2

Add the greeting text inside the div

Inside the <div> element of the Greeting component, add the text Hello, friend! exactly.

React

function Greeting() {
  return {/* Add text here */};
}

export default Greeting;

Hint

Put the text inside the <div> tags like this: <div>Hello, friend!</div>.

3

Use the Greeting component in an app

Create a React functional component named App that returns the <Greeting /> component inside a <main> element. Export App as default.

React

function Greeting() {
  return Hello, friend!;
}

// Your code here to create App component

Hint

Create function App() { return <main><Greeting /></main>; } and export it.

4

Explain the component output

Add a comment above the Greeting component explaining that it shows the text "Hello, friend!" on the page.

React

// Your comment here
function Greeting() {
  return Hello, friend!;
}

function App() {
  return ;
}

export default App;

Hint

Write a comment starting with // describing what the Greeting component does.

Practice

1. What is a React component?

easy

A. A reusable piece of UI built with a function or class

B. A special type of variable that stores data

C. A tool to style HTML elements

D. A command to run React apps

Solution

1. Step 1: Understand React components

   A React component is a building block of UI that can be reused multiple times.

2. Step 2: Identify the correct definition

   Only A reusable piece of UI built with a function or class describes a reusable UI piece built with a function or class.

3. Final Answer:

   A reusable piece of UI built with a function or class -> Option A

4. Quick Check:

   Component = reusable UI block [OK]

Hint: Components are reusable UI parts made with functions [OK]

Common Mistakes:

• Confusing components with variables
• Thinking components are styling tools
• Believing components are commands

2. Which of the following is the correct way to define a React functional component?

easy

A. const MyComponent = 'Hello';

B. function MyComponent() { return Hello; }

C. var MyComponent = Hello;

D. class MyComponent extends React.Component { }

Solution

1. Step 1: Review functional component syntax

   A functional component is a function returning JSX, like function MyComponent() { return
   Hello; }.

2. Step 2: Check each option

   function MyComponent() { return
   Hello
   ; } matches the correct syntax. var MyComponent =
   Hello
   ; assigns JSX directly to a variable, which is not a component. const MyComponent = 'Hello'; assigns a string, not JSX. class MyComponent extends React.Component { } is a class component, not functional.

3. Final Answer:

   function MyComponent() { return <div>Hello</div>; } -> Option B

4. Quick Check:

   Functional component = function returning JSX [OK]

Hint: Functional components are functions returning JSX [OK]

Common Mistakes:

• Assigning JSX directly to variables
• Using strings instead of JSX
• Confusing functional and class components

3. What will this React component render?

function Greeting() {
  return <h1>Hello, world!</h1>;
}

medium

A. Nothing, because the function is not called

B. An error because of missing parentheses

C. <h1>Hello, world!</h1> displayed on the page

D. A blank page with no content

Solution

1. Step 1: Understand component return value

   The component returns an <h1> element with text "Hello, world!" which React renders as HTML.

2. Step 2: Confirm rendering behavior

   When used in JSX, this component will display the heading on the page. No syntax errors exist.

3. Final Answer:

   <h1>Hello, world!</h1> displayed on the page -> Option C

4. Quick Check:

   Return JSX renders UI [OK]

Hint: Returned JSX shows on page when component is used [OK]

Common Mistakes:

• Thinking function must be called manually
• Assuming missing parentheses cause error here
• Believing component renders nothing by default

4. Identify the error in this React component:

function Welcome() {
  return <div>Welcome to React</div>
}

medium

A. Missing semicolon after return statement

B. JSX must be wrapped in parentheses if on multiple lines

C. Function name should start with lowercase letter

D. No error, component is correct

Solution

1. Step 1: Check JSX syntax

   The JSX is a single line and correctly returned without parentheses, which is valid.

2. Step 2: Verify naming and semicolon rules

   Function names for components should start uppercase, which is true. Semicolons are optional in JavaScript here.

3. Final Answer:

   No error, component is correct -> Option D

4. Quick Check:

   Valid JSX and naming means no error [OK]

Hint: JSX on one line doesn't need parentheses [OK]

Common Mistakes:

• Thinking semicolons are mandatory after return
• Believing lowercase function names are required
• Assuming JSX always needs parentheses

5. You want to create a reusable button component that shows different text based on a property. Which is the best way to do this?

hard

A. function Button(props) { return {props.text}; }

B. function Button() { return Click me; }

C. const Button = Click me;

D. function Button(text) { return {text}; }

Solution

1. Step 1: Understand passing data to components

   Props are used to pass data to components. Using props.text allows dynamic button text.

2. Step 2: Evaluate each option

   function Button(props) { return {props.text}; } correctly uses props to show different text. function Button() { return Click me; } always shows fixed text. const Button = Click me; is not a function component. function Button(text) { return {text}; } incorrectly uses a parameter instead of props object.

3. Final Answer:

   function Button(props) { return <button>{props.text}</button>; } -> Option A

4. Quick Check:

   Use props for dynamic content [OK]

Hint: Use props to pass dynamic text to components [OK]

Common Mistakes:

• Hardcoding text inside component
• Not using props object for parameters
• Assigning JSX directly to variables