State vs Props in React

In React, the two main concepts that govern the data flow within a component are State and Props. Understanding the difference between these two is crucial for building effective and maintainable React applications. Let’s dive in.

State

State refers to the internal data of a component. It represents the current condition or properties of the component. State is managed within the component itself and can be updated using the setter from your useState() hook method.

State is typically initialized in the component’s constructor if using a Class based component, or by using the useState() hook when using a Functional component. Typically when working on newer applications, you’ll be using functional components. If you’d like to learn more about React hooks and what all changed with their release, read my blog post about it. You can find the post here.

Some key characteristics of State:

• State is local to the component
• State is private to the component
• State can be changed over time

Here’s an example of what it looks like:

import React, { useState } from 'react';

function JumpMan() {
  const [jumps, setJumps] = useState(0);
  return (
    <div>
      <p>You jumped {jumps} times.</p>
      <button onClick={()=> setJumps(jumps + 1)}>Jump Again!</button>
    </div>
  );
}

As you can see, jumps is the state, and setJumps is what is called to update the state. Every time the button is clicked, setJumps is called and increases jumps by 1.

Props

Props, on the other hand, are the input parameters that are passed down to a component from its parent. They are immutable, meaning they cannot be changed by the child component.

Some key characteristics of Props:

• Props are passed from parent to child components
• Props are read-only and cannot be modified by the child component
• Props are used to make components more reusable and flexible

Props allow you to customize the behavior and appearance of a component without modifying the component itself. They provide a way to pass data down the component tree, enabling parent components to control the state and behavior of their children. This separation of concerns promotes modularity and makes components more independent and reusable.

Here’s an example of what it looks like:

import React from 'react';
import ChildComponent from './ChildComponent';

const ParentComponent = () => {
  const message = "Hello from the parent component!";

  return (
    <div>
      <h1>Parent Component</h1>
      {/* Passing the 'message' prop to the ChildComponent */}
      <ChildComponent message={message} />
    </div>
  );
};

export default ParentComponent;

import React from 'react';

const ChildComponent = ({ message }) => {
  return (
    <div>
      <h2>Child Component</h2>
      {/* Accessing the 'message' prop passed from the ParentComponent */}
      <p>{message}</p>
    </div>
  );
};

export default ChildComponent;

In this example, the parent component ParentComponent defines a variable called message. It then passes this message down to its child component ChildComponent via message={message} The child component receives the message prop and displays it using {message}.

Props are a powerful tool for building composable and flexible React components. By passing data through props, you can create reusable components that can be easily integrated into different parts of your application. This promotes a unidirectional data flow, where data moves from parent to child, making the application more predictable and easier to reason about.

Conclusion

Understanding the difference between state and props is essential for managing the data flow in your React applications. State is used for managing the internal data of a component, while props are used for passing data from parent to child components.

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Comments

[Peter Vivo]

State is local to the component -> and can be passed to any component below.
State is immutable, just modify by action or setStateAction.
Action can be passed down also to any component below, or using context, or using global state handler like redux.

[Travis Ramos]

Yep, exactly Peter! And when passed down to a component below (child component) it becomes a prop!

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