next.js/packages/next/src/client/components/is-next-router-error.ts

import {
  isHTTPAccessFallbackError,
  type HTTPAccessFallbackError,
} from './http-access-fallback/http-access-fallback'
import { isRedirectError, type RedirectError } from './redirect-error'

/**
 * Returns true if the error is a navigation signal error. These errors are
 * thrown by user code to perform navigation operations and interrupt the React
 * render.
 */
export function isNextRouterError(
  error: unknown
): error is RedirectError | HTTPAccessFallbackError {
  return isRedirectError(error) || isHTTPAccessFallbackError(error)
}