Expert-Level Explanation

Portals in React provide a way to render children into a DOM node that exists outside the DOM hierarchy of the parent component. This is particularly useful when you need to break out of the current HTML flow, such as when rendering modals, tooltips, or dialogues. A common use case is to render a modal dialogue that visually breaks out of its parent component but maintains all React behaviours like event handling and context.

Creative Explanation

Imagine you're painting a mural on a wall (a React component tree), but suddenly you need to paint part of it on a completely different wall, perhaps in another room (somewhere else in the DOM). Portals allow you to do this seamlessly. You can start painting on one wall and continue on another while still considering it part of the original artwork.

Practical Explanation with Code

Using Portals in React:

import React from 'react';
import ReactDOM from 'react-dom';

class MyModal extends React.Component {
  render() {
    return ReactDOM.createPortal(
      this.props.children,
      document.getElementById('modal-root')
    );
  }
}

// Usage
<MyModal>
  <p>This is rendered in a modal!</p>
</MyModal>

In this example, MyModal uses ReactDOM.createPortal to render its children into a DOM node identified by'modal-root', which is typically located outside the main app's DOM hierarchy.

Real-World Example

In a web application like an online store, portals can be used for rendering product zoom modals. When a user clicks on a product image, a full-screen modal with the zoomed-in image opens up, rendered using a portal, so it overlays the rest of the page content.