Props in React: Passing Data Between Components

What Are Props?

Props (short for "properties") are used to pass data from a parent component to a child component in React. Props make components reusable and dynamic.

Props are:

• Immutable (Cannot be changed inside the component)
• Passed from parent to child
• Read-only

---

Using Props in Functional Components

Example: Passing Props to a Child Component

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

function App() {
  return <Greeting name="Alice" />;
}

export default App;

The Greeting component receives the name prop and displays "Hello, Alice!".

---

Using Props in Class Components (Older Method)

import React, { Component } from "react";

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

function App() {
  return <Greeting name="Alice" />;
}

export default App;

Functional components are preferred for props handling.

---

Default Props

You can set default values for props using defaultProps.

Example: Default Props in Functional Components

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

export default Greeting;

or using defaultProps:

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

---

Props as Objects (props vs. Destructuring)

Props are passed as an object. You can access them directly using props or destructure them.

Using props object:

function User(props) {
  return <h1>{props.name} is {props.age} years old</h1>;
}

Using destructuring:

function User({ name, age }) {
  return <h1>{name} is {age} years old</h1>;
}

Destructuring is preferred for cleaner code.

---

Passing Functions as Props

Example: Child Component Calls Parent Function

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

function App() {
  const handleClick = () => {
    alert("Button clicked!");
  };

  return <Button onClick={handleClick} />;
}

export default App;

The onClick function is passed from App to Button.

---

Passing Components as Props (children Prop)

Props can also include React elements or components.

Example: Using children Prop

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

function App() {
  return (
    <Card>
      <h2>Title</h2>
      <p>This is content inside the card.</p>
    </Card>
  );
}

export default App;

The children prop lets you wrap elements inside a component.

---

Props vs. State (Key Differences)

Feature	Props ( Passed from Parent)	State ( Internal to Component)
Mutability	Immutable	Mutable
Where Defined?	Parent Component	Inside the Component
How to Update?	Cannot be changed	Use useState()

---

Summary

• Props allow data flow from parent to child.
• Props are immutable (read-only).
• Props can be objects, functions, or even React elements.
• Use children prop to pass JSX inside components.