ActiveClassName

activeClassName is a prop commonly found in routing libraries for JavaScript frameworks like React. Its primary purpose is to specify a CSS class name that will be applied to a link element when its corresponding route is active. This allows developers to visually indicate to the user which page or section of the application they are currently viewing.

When a user navigates to a route that matches the `to` prop of a link component that supports `activeClassName`, the library automatically adds the specified `activeClassName` string to the element's `className` attribute. This is typically done in conjunction with CSS styling. For example, a developer might define CSS rules for `.active-link` to change the color, font weight, or add an underline to the active link, making it stand out from other navigation items.

The exact implementation and availability of `activeClassName` can vary slightly between different routing libraries. Some libraries might offer alternative props or methods for achieving similar functionality, such as `activeStyle` for inline styles or callback functions that provide more granular control over the active state. However, `activeClassName` remains a widely adopted and straightforward approach for styling active navigation links. It simplifies the process of providing clear visual feedback to users about their current location within a single-page application.