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⚓ React Props – Passing Data to Components in React (2025 Guide)

🧲 Introduction – Why Props Are Essential in React

In React.js, props (short for properties) are a vital mechanism for passing data between components. They enable component reusability and dynamic UI rendering, allowing developers to build flexible and maintainable user interfaces.

Without props, every component would be isolated and hardcoded, defeating the purpose of React’s component-based architecture.

🎯 In this guide, you’ll learn:

What props are and how they work in React
How to pass and access props
Props with functional and class components
Default props, prop types, and best practices

📦 What Are Props in React?

Props are read-only inputs passed from a parent component to a child component. They help customize how a component behaves or what it displays.

📘 Think of props like HTML attributes:

<Greeting name="Alice" />

Here, name="Alice" is a prop passed to the Greeting component.

🧩 Functional Components with Props

✅ Example:

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

✅ Destructured Version:

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

🏛️ Class Components with Props

In class components, props are accessed using this.props.

class Greeting extends React.Component {
  render() {
    return <h1>Hello, {this.props.name}!</h1>;
  }
}

📦 Passing Multiple Props

Props can be strings, numbers, arrays, objects, or even functions.

function User({ name, age, hobbies }) {
  return (
    <div>
      <h2>{name}, {age}</h2>
      <ul>
        {hobbies.map(hobby => <li key={hobby}>{hobby}</li>)}
      </ul>
    </div>
  );
}

// Usage
<User name="Sam" age={25} hobbies={['Reading', 'Coding']} />

🧠 Props Are Immutable

Props cannot be changed by the receiving component.

// ❌ This is NOT allowed
props.name = "John";

🔐 If a component needs to manage or change its own data, use state, not props.

🧰 Passing Functions as Props (Callback Props)

Props can be used to pass event handlers or custom logic.

Example:

function Button({ onClick }) {
  return <button onClick={onClick}>Click Me</button>;
}

function App() {
  const showAlert = () => alert("Button Clicked!");
  return <Button onClick={showAlert} />;
}

📌 This allows child components to communicate with parents.

📋 Default Props

Default values can be defined for props in case none are provided.

Functional Components:

function Greeting({ name = "Guest" }) {
  return <h1>Hello, {name}</h1>;
}

With `defaultProps`:

Greeting.defaultProps = {
  name: "Guest"
};

📏 Validating Props with PropTypes

Use PropTypes to validate types of props passed to a component.

Step 1: Install PropTypes

npm install prop-types

Step 2: Use It in Component

import PropTypes from 'prop-types';

function Greeting({ name, age }) {
  return <h2>{name} is {age} years old.</h2>;
}

Greeting.propTypes = {
  name: PropTypes.string.isRequired,
  age: PropTypes.number
};

🧱 Use Case: Composing Components with Props

function Card({ title, description }) {
  return (
    <div className="card">
      <h3>{title}</h3>
      <p>{description}</p>
    </div>
  );
}

// Usage
<Card title="React Basics" description="Learn JSX, props, and more" />

📦 Props make it easy to reuse components with different content.

📌 Summary – Recap & Next Steps

Props are the primary way to pass dynamic data and behavior into components in React. They promote reusability, flexibility, and clean separation of concerns.

🔍 Key Takeaways:

Props are passed from parent → child component
Props are read-only; don’t modify them inside the component
You can pass anything: strings, numbers, arrays, functions
Use defaultProps and PropTypes for defaults and validation

⚙️ Real-World Relevance:
Props power reusable UIs in production apps like dashboards, modals, and forms — from React websites to mobile apps using React Native.

❓ FAQ Section

❓ What is the difference between props and state?
✅ Props are external data passed to components, while state is internal data managed within the component.

❓ Can props be updated?
✅ No. Props are immutable. To change props, the parent component must pass updated values.

❓ Can I pass functions via props?
✅ Yes! Passing functions (callbacks) is a common pattern for handling events and child-to-parent communication.

❓ Are props passed to all components automatically?
✅ No. You must explicitly pass them when using the component:

<MyComponent name="John" />

❓ Can props have default values?
✅ Yes. Use defaultProps or destructure with default:

function Hello({ name = "Guest" }) { ... }

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