Passing props to components in React - Mini Project: Build & Apply

Passing props to components

📖 Scenario: You are building a simple React app that shows a greeting message for a user. The greeting text should come from a parent component and be passed down to a child component.

🎯 Goal: Build two React functional components: App and Greeting. Pass a message prop from App to Greeting and display it inside Greeting.

📋 What You'll Learn

Create a functional component called App.

Inside App, create a variable greetingMessage with the exact string 'Hello, welcome to React!'.

Create a functional component called Greeting that accepts a message prop.

Render the Greeting component inside App and pass greetingMessage as the message prop.

Inside Greeting, display the message prop inside a <h1> element.

💡 Why This Matters

🌍 Real World

Passing props is how React components share data, like sending user info or settings from a main app to smaller parts of the UI.

💼 Career

Understanding props is essential for React developers to build reusable and interactive components that work together.

1

Create the App component with a greeting message

Create a React functional component called App. Inside it, create a variable called greetingMessage and set it to the string 'Hello, welcome to React!'.

React

function App() {
  // Your code here
}

Hint

Remember to use const to create the greetingMessage variable inside the App function.

2

Create the Greeting component that accepts a message prop

Create a React functional component called Greeting that accepts a single prop named message. The component should return a <div> element for now.

React

function App() {
  const greetingMessage = 'Hello, welcome to React!';
}

// Your code here to create Greeting component

Hint

Use destructuring in the function parameter to get the message prop.

3

Pass the greetingMessage prop from App to Greeting

Inside the App component, return the Greeting component and pass the variable greetingMessage as the message prop.

React

function App() {
  const greetingMessage = 'Hello, welcome to React!';
  // Your code here to return Greeting with message prop
}

function Greeting({ message }) {
  return ;
}

Hint

Use JSX syntax to render <Greeting message={greetingMessage} /> inside App.

4

Display the message prop inside Greeting

Inside the Greeting component, replace the <div> content with an <h1> element that displays the message prop.

React

function App() {
  const greetingMessage = 'Hello, welcome to React!';
  return ;
}

function Greeting({ message }) {
  // Your code here to display message inside 
}

Hint

Use curly braces {} inside JSX to insert the message prop value.

Practice

1. What is the main purpose of props in React components?

easy

A. To handle user events like clicks

B. To store local state inside a component

C. To pass data from a parent component to a child component

D. To style components with CSS

Solution

1. Step 1: Understand the role of props

   Props are used to send data from one component to another, specifically from parent to child.

2. Step 2: Differentiate props from other React features

   State stores local data, events handle interactions, and CSS styles components, but props specifically pass data down.

3. Final Answer:

   To pass data from a parent component to a child component -> Option C

4. Quick Check:

   Props = data passing [OK]

Hint: Props always send data down from parent to child [OK]

Common Mistakes:

• Confusing props with state
• Thinking props handle events
• Believing props style components

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

easy

A.

B.

C.

D.

Solution

1. Step 1: Recall JSX prop syntax

   Props are passed like HTML attributes: name="value" or name={expression}.

2. Step 2: Check each option

   uses correct string syntax.

   misses quotes around string.

   uses invalid quotes.

   uses colon which is invalid in JSX.

3. Final Answer:

   <Header title="Hello" /> -> Option B

4. Quick Check:

   Props look like HTML attributes [OK]

Hint: Use quotes for string props in JSX [OK]

Common Mistakes:

• Omitting quotes for string values
• Using colons instead of equals
• Adding extra quotes around prop names

3. What will be rendered by this React component?

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

// Usage:
<Greeting name="Alice" />

medium

A. Hello, Alice!

B. Hello, {props.name}!

C. Hello, name!

D. Error: props is undefined

Solution

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

   The component receives props and accesses props.name to display the name.

2. Step 2: Check the usage of the component

   The component is called with name="Alice", so props.name is "Alice".

3. Final Answer:

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

4. Quick Check:

   props.name = Alice [OK]

Hint: Props values replace placeholders inside JSX [OK]

Common Mistakes:

• Printing literal {props.name} instead of value
• Forgetting to pass the prop
• Assuming props is undefined

4. Identify the error in this code snippet:

function Welcome(props) {
  return <h2>Welcome, {props.user}!</h2>;
}

// Usage:
<Welcome user=John />

medium

A. Missing quotes around string prop value 'John'

B. Props object is not passed correctly

C. Component name should be lowercase

D. JSX tags are not closed properly

Solution

1. Step 1: Check the prop usage in JSX

   In JSX, string prop values must be quoted, e.g., user="John".

2. Step 2: Identify the error in usage

   The code uses user=John without quotes, causing a syntax error.

3. Final Answer:

   Missing quotes around string prop value 'John' -> Option A

4. Quick Check:

   String props need quotes [OK]

Hint: Always quote string props in JSX [OK]

Common Mistakes:

• Omitting quotes for string props
• Using lowercase component names
• Leaving JSX tags unclosed

5. Given this parent and child component code, what will be the output?

function Child({ message }) {
  return <p>Message: {message || 'No message'}</p>;
}

function Parent() {
  const msg = '';
  return <Child message={msg} />;
}

hard

A. Message:

B. Error: message prop missing

C. Message: undefined

D. Message: No message

Solution

1. Step 1: Analyze the prop value passed

   The parent passes msg which is an empty string '' as the message prop.

2. Step 2: Understand the child component's rendering logic

   The child uses {message || 'No message'}. Since empty string is falsy, it falls back to 'No message'.

3. Final Answer:

   <p>Message: No message</p> -> Option D

4. Quick Check:

   Falsy empty string triggers fallback [OK]

Hint: Falsy props like '' use fallback values in JSX [OK]

Common Mistakes:

• Assuming empty string is truthy
• Expecting empty string to display as is
• Thinking missing prop causes error here