ES6 Modules

ES6 modules are a feature introduced in ECMAScript 6 (ES6) that allows developers to structure their JavaScript code into separate, reusable files (modules). Each module can export certain variables or functions that can be imported and used in other modules. This enables better organization, maintainability, and reusability of code.

In the context of ReactJS, ES6 modules provide a way to structure your React components and services into different files, making your codebase easier to understand and manage.

Here's a simple example of how ES6 modules work with React.

You can define a React component in one file, and export it as a module:

```javascript
// MyComponent.js
import React from 'react';

class MyComponent extends React.Component {
render() {
return <h1>Hello, World!</h1>
}
}

export default MyComponent;
```

This component can then be imported into another file and used:

```javascript
// App.js
import React from 'react';
import MyComponent from './MyComponent.js';

class App extends React.Component {
render() {
return (
<div>
<MyComponent />
</div>
);
}
}

export default App;
```

In this example, `MyComponent.js` exports the `MyComponent` class, and `App.js` imports `MyComponent` from `MyComponent.js`. The `App.js` file can then use `<MyComponent />` in its JSX. This is how ES6 modules facilitate code reusability and organization in React JS applications.