gistfile1.txt

const route = '/products/:id';

type Split<S extends string> = S extends ''
  ? []
  : S extends `${infer C}${infer R}`
  ? [C, ...Split<R>]
  : never

type RequestHandler<TRoute extends string> = {
  params: TRoute extends `${infer _}:${infer R}` ? { 
    [key in R]: string
   } : never;
}

type HandleRoute<TRoute extends string> = (
  request: RequestHandler<TRoute>
) => void;



const routes = {
  'products/:productId': (request) => {
    request.params.productId
  },
  'items/:itemId/reviews': (request) => {
    request.params.itemId
  }
}

const handleProductId: HandleRoute<'products/:productId'> = (request) => {
  request.params.productId
}