Using props in JSX in React

Introduction

Props let you send information to components so they can show different things. It is like giving a friend a note with instructions.

You want to show a greeting with a person's name.

You need to reuse a button but with different labels.

You want to display a list of items with different details.

You want to customize a component's color or style from outside.

Syntax

React

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

// Or using destructuring
function ComponentName({ propertyName }) {
  return <div>{propertyName}</div>;
}

Props are passed like attributes in HTML: <ComponentName propertyName="value" />.

You can use curly braces {} inside JSX to show JavaScript values.

Examples

This shows a greeting with the name passed as a prop.

React

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

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

The button text changes based on the label prop.

React

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

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

You can pass multiple props to customize content and style.

React

function Message({ text, color }) {
  return <p style={{ color: color }}>{text}</p>;
}

// Usage:
<Message text="Hi there!" color="blue" />

Sample Program

This app shows two greetings with different names using the same Greeting component and props.

React

import React from 'react';

function Greeting({ name }) {
  return <h2>Hello, {name}!</h2>;
}

export default function App() {
  return (
    <main>
      <Greeting name="Sam" />
      <Greeting name="Lee" />
    </main>
  );
}

Important Notes

Props are read-only inside the component. To change data, use state instead.

Always use meaningful prop names to keep code clear.

Summary

Props send data from parent to child components.

Use curly braces {} in JSX to show prop values.

Props help reuse components with different content.

Practice

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

easy

A. To handle user events like clicks

B. To store internal state within a component

C. To style components with CSS

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

Solution

1. Step 1: Understand the role of props

   Props are used to send data from a parent component to a child component in React.

2. Step 2: Differentiate props from other concepts

   State stores internal data, events handle user actions, 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 D

4. Quick Check:

   Props = Data passing [OK]

Hint: Props always send data 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 use a prop named title inside JSX?

easy

A. <h1>title</h1>

B. <h1>{title}</h1>

C. <h1>{props.title}</h1>

D. <h1>$title</h1>

Solution

1. Step 1: Use curly braces to embed prop values in JSX

   In JSX, to show a prop value, you wrap the prop access in curly braces like {props.title}.

2. Step 2: Understand context of prop usage

   The props object is passed to the component function, so access via {props.title}. Using {title} requires destructuring like function Comp({title}).

3. Final Answer:

   <h1>{props.title}</h1> -> Option C

4. Quick Check:

   Curly braces show prop values [OK]

Hint: Use curly braces { } to show props in JSX [OK]

Common Mistakes:

• Writing prop name as plain text without braces
• Using $ sign like in other languages
• Using {title} without destructuring the props object

3. Given the component:

function Greeting(props) {
  return <h2>Hello, {props.name}!</h2>;
}

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

What will be rendered on the screen?

medium

A. Hello, {name}!

B. Hello, Alice!

C. Hello, props.name!

D. SyntaxError

Solution

1. Step 1: Identify how props are passed and used

   The Greeting component receives a prop called name with value "Alice".

2. Step 2: Understand JSX rendering with props

   The JSX uses {props.name} which inserts the string "Alice" inside the <h2> tag.

3. Final Answer:

   <h2>Hello, Alice!</h2> -> Option B

4. Quick Check:

   props.name = Alice [OK]

Hint: Props values appear inside curly braces in JSX output [OK]

Common Mistakes:

• Expecting literal text {name} instead of value
• Confusing props.name with string 'props.name'
• Thinking this causes syntax error

4. What is wrong with this React component code?

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

medium

A. props.name should be inside curly braces to render its value

B. Function name should be lowercase

C. Missing return statement

D. JSX tags must be self-closing

Solution

1. Step 1: Check how props are used inside JSX

   The code writes props.name as plain text inside JSX, so it will render literally instead of the prop value.

2. Step 2: Correct usage of props in JSX

   To show the value of props.name, it must be wrapped in curly braces like {props.name}.

3. Final Answer:

   props.name should be inside curly braces to render its value -> Option A

4. Quick Check:

   Use {props.name} to show prop value [OK]

Hint: Always wrap props in { } inside JSX [OK]

Common Mistakes:

• Writing props.name as plain text
• Thinking function names must be lowercase
• Confusing JSX self-closing rules

5. You want to create a reusable Button component that shows different text based on a label prop. Which code correctly uses props to achieve this?

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

Choose the correct replacement for ???.

hard

A. {props.label}

B. {label}

C. "props.label"

D. label

Solution

1. Step 1: Understand how to access props inside the component

   The component receives props as an object, so the label prop is accessed as props.label.

2. Step 2: Use curly braces to embed the prop value in JSX

   To show the value inside JSX, wrap props.label in curly braces: {props.label}.

3. Final Answer:

   {props.label} -> Option A

4. Quick Check:

   Use {props.propName} to show prop value [OK]

Hint: Use {props.propName} inside JSX to show prop values [OK]

Common Mistakes:

• Using prop name without braces
• Using braces without props object
• Using quotes around prop name