building user interfaces, especially for single-page applications. It uses a component-based structure that makes development more efficient and maintainable. In React, different file extensions are used for specific purposes: .js or .jsx for JavaScript and JSX code.

Understanding these extensions is important for improving code readability, fixing bugs in your project.

Difference Between a .js and .jsx File in React
Here is a detailed comparison of .js and .jsx files based on various features:

.js File .jsx File
Used for regular JavaScript code. Used for React components with HTML-like code (JSX).
Doesn’t include JSX syntax. Includes JSX syntax to define the UI.
Best for writing logic, utility functions, and simple components. Best for writing UI components that need JSX to render content.
Doesn’t need extra tools to run. Needs tools like Babel to convert JSX to JavaScript.
Smaller and simpler if just handling logic. Larger due to JSX code for user interfaces.
Can be used for both JavaScript and React logic. Focused mainly on creating and rendering UI.
What are .js files in React?
The .js file is a file that contains standard JavaScript code. These files do not contain the UI related code and are used for writing the logics and the functions.

Used for regular JavaScript code and logic.
Does not include JSX (HTML-like syntax).
Can be used for utility functions, state management, or simple React components.
No extra tools needed to run.
Now, let us understand with the help of the example:

// MyComponent.js
import React from 'react';
const MyComponent = () => {
return React.createElement('h1', null, 'Hello, World!');
};
export default MyComponent;
In this example:

The component is created using React.createElement() instead of JSX.

Example:Get your own React.js Server
Here is an example of a Hook. Don't worry if it doesn't make sense. We will go into more detail in the next section.

import React, { useState } from "react";
import ReactDOM from "react-dom/client";

function FavoriteColor() {
const [color, setColor] = useState("red");

return (
<>

My favorite color is {color}!

type="button"
onClick={() => setColor("blue")}
>Blue
type="button"
onClick={() => setColor("red")}
>Red
type="button"
onClick={() => setColor("pink")}
>Pink
type="button"
onClick={() => setColor("green")}
>Green
</>
);
}

const root = ReactDOM.createRoot(document.getElementById('root'));
root.render();

Hook Rules
There are 3 rules for hooks:

Hooks can only be called inside React function components.
Hooks can only be called at the top level of a component.
Hooks cannot be conditional
Note: Hooks will not work in React class components.

Custom Hooks
If you have stateful logic that needs to be reused in several components, you can build your own custom Hooks.

We'll go into more detail in the Custom Hooks section