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---
title: default.js
description: API Reference for the default.js file.
related:
title: Learn more about Parallel Routes
links:
- app/api-reference/file-conventions/parallel-routes
---
The `default.js` file is used to render a fallback within [Parallel Routes](/docs/app/api-reference/file-conventions/parallel-routes) when Next.js cannot recover a [slot's](/docs/app/api-reference/file-conventions/parallel-routes#slots) active state after a full-page load.
During [soft navigation](/docs/app/getting-started/linking-and-navigating#client-side-transitions), 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.
<Image
alt="Parallel Routes unmatched routes"
srcLight="/docs/light/parallel-routes-unmatched-routes.png"
srcDark="/docs/dark/parallel-routes-unmatched-routes.png"
width="1600"
height="930"
/>
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, a `404` is rendered instead.
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.
## Reference
### `params` (optional)
A promise that resolves to an object containing the [dynamic route parameters](/docs/app/api-reference/file-conventions/dynamic-routes) from the root segment down to the slot's subpages. For example:
```tsx filename="app/[artist]/@sidebar/default.js" switcher
export default async function Default({
params,
}: {
params: Promise<{ artist: string }>
}) {
const { artist } = await params
}
```
```jsx filename="app/[artist]/@sidebar/default.js" switcher
export default async function Default({ params }) {
const { artist } = await params
}
```
| Example | URL | `params` |
| ------------------------------------------ | ------------ | -------------------------------------------- |
| `app/[artist]/@sidebar/default.js` | `/zack` | `Promise<{ artist: 'zack' }>` |
| `app/[artist]/[album]/@sidebar/default.js` | `/zack/next` | `Promise<{ artist: 'zack', album: 'next' }>` |
- Since the `params` prop is a promise. You must use `async/await` or React's [`use`](https://react.dev/reference/react/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.
|