route.ts

class Route {
  urlPattern: URLPattern
  constructor (
    public method: string,
    public pathname: string,
    public handler: (req: Request) => Promise<Response> | Response
  ) {
    this.urlPattern = new URLPattern({ pathname })
  }
}

class Routes {
  routes: Route[]
  constructor (...routes: Route[]) {
    this.routes = routes
  }
  async match (req: Request): Promise<Response> {
    const matches = this.routes.filter(route => {
      return route.urlPattern.test(req.url) && route.method === req.method
    })
    if (matches.length > 1) { 
      return new Response('internal error, more then one route with the same pathname')
    } else if (matches.length === 0) {
      return new Response('internal error, not found')
    } else {
      const response = await matches[0].handler(req)
      
      return response
    }
  }
}

const application = (database) => {
  const elephant = new Route("GET", '/elephant', (req: Request) => {
    // access database here database
    if (new URL(req.url).searchParams.get('name') === 'dumbo') {
      return new Response('dumbo')
    }
    return new Response('invalid route')
  })

  const routes = new Routes(
    elephant,
  )

  return routes
}

application({} /** example db pass here */).match(request)