How Props and State Differ in React

Introduction

In React, props and state are two important ways to handle data in your applications. While they might seem similar at first, they serve different purposes. Understanding the differences between them is crucial for building effective React apps.

What Are Props?

Props, short for properties, are a way to pass data from one component to another. Think of them like arguments to a function. When you create a component, you can give it props to customize its output. This makes components reusable and helps to keep your code organized.

Here's a simple example:

<code class="javascript">
function Greeting(props) {
    return <h1>Hello, {props.name}!</h1>;
}

In the code above, the Greeting component takes a prop called name. You can use this component like this:

<code class="javascript">
<Greeting name="Alice" />

This will render: Hello, Alice!. The value of name can change when you use the component but cannot change within the Greeting component itself. This is a key point: props are read-only.

What Is State?

State, on the other hand, is used to manage data that can change over time in a component. Unlike props, state is local to a component. Changing the state will cause the component to re-render and show the updated information.

Here’s how you can use state in a component:

<code class="javascript">
import React, { useState } from 'react';

function Counter() {
    const [count, setCount] = useState(0);

    return (
        <div>
            <p>Count: {count}</p>
            <button onClick={() => setCount(count + 1)}>Increase</button>
        </div>
    );
}

In the Counter component above, we use the useState hook to create a state variable called count. The button allows users to increase the count. Each time the button is clicked, the state changes, and the component updates to show the new count.

Key Differences Between Props and State

• Source of Truth: Props come from parent components, while state is local to the component itself.
• Mutability: Props are read-only. You cannot change them from within the component. State is mutable, meaning you can change it using the setState function.
• Purpose: Use props to pass data and functions down to child components. Use state to control data that may change over time.

When to Use Props and State

Here’s the thing: knowing when to use props and state can really improve your React app. If you want to share data between components, use props. If you want a component to manage its own data (like form input or a toggle), use state.

Let’s break it down with examples:

1. If your component needs to display data from its parent, use props.
2. If your component needs to track user input, use state.
3. If you need to perform actions based on user events, like clicking a button, you may use state to control what happens next.

Conclusion

Understanding the difference between props and state is key in React development. Props are used to pass data to components, while state is used to manage changing data within a component. By knowing how and when to use each, you can create more powerful and efficient applications.

For more information on React, check out the official React documentation.