default.js

The default.js file is used to render a fallback within Parallel Routes when Next.js cannot recover a slot's active state after a full-page load.

During soft navigation, Next.js keeps track of the active state (subpage) for each slot. However, for hard navigations (full-page load), Next.js cannot recover the active state. In this case, a default.js file can be rendered for subpages that don't match the current URL.

Consider the following folder structure. The @team slot has a settings page, but @analytics does not.

When navigating to /settings, the @team slot will render the settings page while maintaining the currently active page for the @analytics slot.

On refresh, Next.js will render a default.js for @analytics. If default.js doesn't exist, an error is returned for named slots (@team, @analytics, etc) and requires you to define a default.js in order to continue. If you want to preserve the old behavior of returning a 404 in these situations, you can create a default.js that contains:

import { notFound } from 'next/navigation'
 
export default function Default() {
  notFound()
}

Additionally, since children is an implicit slot, you also need to create a default.js file to render a fallback for children when Next.js cannot recover the active state of the parent page. If you don't create a default.js for the children slot, it will return a 404 page for the route.

Reference

params (optional)

A promise that resolves to an object containing the dynamic route parameters from the root segment down to the slot's subpages. For example:

export default async function Default({
  params,
}: {
  params: Promise<{ artist: string }>
}) {
  const { artist } = await params
}

export default async function Default({ params }) {
  const { artist } = await params
}

• Since the params prop is a promise. You must use async/await or React's use function to access the values.
  • In version 14 and earlier, params was a synchronous prop. To help with backwards compatibility, you can still access it synchronously in Next.js 15, but this behavior will be deprecated in the future.