Global Variable

Global variables in React JS, similar to global variables in other programming languages, refer to variables that are declared outside of any function and are accessible from any part of the code in your React application.

Generally, Global Variables are not recommended to use in React due to potential issues with state management, security, and debugging. It's often better to manage state locally within each component or use state management libraries like Redux.

However, if you really need to use a global variable in React, they are usually defined in the global scope. To create a global variable in React, you can create a `globals.js` file where you define and export your globals. You can then import this file wherever you need it in your app:

```javascript
//globals.js
export const globalVar = 'Global Variable';

//App.js
import {globalVar} from './globals.js';
console.log(globalVar); // Output: 'Global Variable'
```

Remember, although you can use global variables in React, it's generally better practice to avoid them and find other ways to manage and share state in your app. For example, you can use props to pass data to child components, or use Context API or Redux for state management.