Error: NextRouter was not mounted

Shivan M.

—January 15, 2024

The ProblemThe Problem

When using the useRouter hook in Next.js 13 or later, you may encounter the following error:

Error: NextRouter was not mounted

This error can occur in one of two ways:

1. When a component uses the useRouter hook outside of a Next.js application, or when a router is rendered outside of a Next.js application - like during unit testing.
2. When trying to use the useRouter hook from the next/router package when using the App Directory. This is because the App Router (from next/navigation) has a different behavior from the useRouter hook used in pages.

The SolutionThe Solution

Ensure you are using the correct useRouter hook. If you are using the App Directory, check that the useRouter hook is imported from next/navigation and not from next/router.

When using the useRouter hook from next/navigation, use the following guidelines:

• Instead of pathname, use the usePathname() hook.
• Instead of the query object, use the useSearchParams() hook.

Mock next/navigation When Writing Unit TestsMock next/navigation When Writing Unit Tests

The above error can also occur when using the useRouter hook from next/navigation in unit tests. It might be a good idea to use the next-router-mock package to mock it.

Ensure you mock the new hooks, usePathname() and useSearchParams(), for example:

const nextRouterMock = require('next-router-mock')

jest.mock('next/navigation', () => {
  const { useRouter } = nextRouterMock

  const usePathname = () => {
    const router = useRouter()
    return router.pathname
  }

  const useSearchParams = () => {
    const router = useRouter()
    return new URLSearchParams(router.query)
  }

  return {
    useRouter,
    usePathname,
    useSearchParams
  }
})