Add generic typing for Router.add handler

[hariria]

Problem

I want to have strong typing but currently the Router class' add function has a signature like so:

export declare class Router {
	add<T extends RegExp>(method: Method, route: T, handler: Handler<Params>): void;
	...
}

The problem is that handler has a signature like so:

export type Handler<P extends Params = Params> = (req: ServerRequest<P>, res: ServerResponse) => Promisable<Response|void>;

Because the Router's add function is Handler<Params> and not Handler<P extends Params = Params>, this prevents people from adding handlers to the Router.add function that implement a type P that extends Params

Solution

would be nice to change to something like

	add<T extends RegExp, P extends Params = Params>(method: Method, route: T, handler: Handler<P>): void;

Context

The reason why is because atm when I do something like

import { listen, Router } from 'worktop';

export interface VerifyParams extends Params {
  address: string;
  anotherParam: string;
}

export const verify: Handler<VerifyParams> = async (
  req,
  res,
) => {
  const { address, anotherParam } = req.params;
  const isVerified = address === 'hi' && anotherParam === 'also hi';
  res.send(200, { isVerified }, { 'cache-control': 'private,max-age=30' });
};

const API = new Router();
API.add<RegExp>('GET', /verify/, verify);

this throws the error

Argument of type 'Handler<VerifyParams>' is not assignable to parameter of type 'Handler<Params>'.
  Type 'Params' is missing the following properties from type 'VerifyParams': address, anotherParam