3. Route Slots

Parallel Routes

Parallel Routes in Next.js enable the simultaneous or conditional rendering of multiple pages or components within the same layout. This is especially beneficial for sections of an application that require dynamic content changes without navigating away from the page, like social media feeds or analytics dashboards.

Key Benefits of Parallel Routes:

Simultaneous Rendering: Multiple components or pages can be rendered at the same time within the same layout, enhancing the user experience by providing a composite view of related content.
Conditional Rendering: Depending on the application state or user actions, specific components can be rendered, allowing for a highly responsive and interactive interface.

Route Slots

Route Slots are a method of implementing Parallel Routes using a named slot system, defined by the @folder convention. Slots act like containers for different segments of the application, which are then rendered as props in a shared parent layout.

How Slots Work:

File Structure: Slots are organized in the file system using the @ prefix (e.g., @analytics and @team folders). This structure delineates different areas of the application that can be loaded independently but displayed together.
Component Integration: In the parent layout component, slots are passed as props and rendered alongside the standard children. This allows for a modular approach where the parent layout controls the arrangement and visibility of various slots based on the application logic or routing conditions.

Example Usage:

Imagine a dashboard where user role determines visibility of certain data panels:

An admin might see both team performance metrics and detailed analytics.
A team member might only see relevant team data and some summary analytics.

Active State and Navigation

Next.js manages the active state for each slot, ensuring that the content within each slot is appropriate to the current navigation context.

Navigation Types:

Soft Navigation: Changes content within a slot during client-side navigation without reloading the entire page. This maintains the state of other slots, ensuring a seamless user experience.
Hard Navigation: On a full page reload, Next.js will attempt to recover the state of slots. If it cannot determine the active state for a slot, a default component (usually default.js) is rendered, or a 404 error if no default exists.