# abortNavigation
> abortNavigation is a helper function that prevents navigation from taking place and throws an error if one is set as a parameter.
`abortNavigation` is only usable inside a [route middleware handler](/docs/4.x/directory-structure/app/middleware).
## Type
```ts [Signature]
export function abortNavigation (err?: Error | string): false
```
## Parameters
### `err`
- **Type**: [`Error`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) | `string`
Optional error to be thrown by `abortNavigation`.
## Examples
The example below shows how you can use `abortNavigation` in a route middleware to prevent unauthorized route access:
```ts [app/middleware/auth.ts]
export default defineNuxtRouteMiddleware((to, from) => {
const user = useState('user')
if (!user.value.isAuthorized) {
return abortNavigation()
}
if (to.path !== '/edit-post') {
return navigateTo('/edit-post')
}
})
```
### `err` as a String
You can pass the error as a string:
```ts [app/middleware/auth.ts]
export default defineNuxtRouteMiddleware((to, from) => {
const user = useState('user')
if (!user.value.isAuthorized) {
return abortNavigation('Insufficient permissions.')
}
})
```
### `err` as an Error Object
You can pass the error as an [`Error`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error) object, e.g. caught by the `catch`-block:
```ts [app/middleware/auth.ts]
export default defineNuxtRouteMiddleware((to, from) => {
try {
/* code that might throw an error */
} catch (err) {
return abortNavigation(err)
}
})
```
---
- [Source](https://github.com/nuxt/nuxt/blob/main/packages/nuxt/src/app/composables/router.ts)