feat(router): add compose utility;

- TODO: Deal w/ type-inference mayhem another time.
- Related #7

src/router.d.ts

@@ -55,3 +55,8 @@ export declare class Router {
 
 // TODO?: worktop/status | worktop/errors
 export declare var STATUS_CODES: Record<string|number, string>;
+
+/**
+ * Compose multiple `Handler` functions together, creating a final handler.
+ */
+export function compose<P extends Params = Params>(...handlers: Handler<P>[]): Handler<P>;

src/router.ts

@@ -19,6 +19,15 @@ export function listen(handler: ResponseHandler): void {
 	addEventListener('fetch', reply(handler));
 }
 
+export function compose(...handlers: Handler[]): Handler {
+	return async function (req, res) {
+		for (let handler of handlers) {
+			let tmp = await handler(req, res);
+			if (tmp instanceof Response) return tmp;
+			if (res.finished) return new Response(res.body, res);
+		}
+	};
+}
 interface Entry {
 	keys: string[];
 	handler: Handler;

types/check.ts

@@ -4,7 +4,7 @@ import * as Base64 from 'worktop/base64';
 import { Database, until } from 'worktop/kv';
 import { ServerResponse } from 'worktop/response';
 import { byteLength, HEX, uid, uuid } from 'worktop/utils';
-import { listen, reply, Router, STATUS_CODES } from 'worktop';
+import { listen, reply, Router, compose, STATUS_CODES } from 'worktop';
 
 import type { KV } from 'worktop/kv';
 import type { UID, UUID } from 'worktop/utils';
@@ -336,6 +336,25 @@ API.add('GET', /^[/]foobar[/]?/, (req) => {
 	assert<string>(req.params.anything);
 });
 
+/**
+ * WORKTOP/ROUTER
+ * > COMPOSE
+ */
+
+API.add('GET', '/foo/:bar?', compose(
+	(req, res) => {
+		assert<string|void>(req.params.bar);
+	},
+	async (req, res) => {
+		assert<string|void>(req.params.bar);
+		res.end('hello');
+	},
+	// @ts-expect-error
+	(req, res) => {
+		assert<string|void>(req.params.bar);
+		return 123;
+	}
+));
 
 /**
  * WORKTOP/CACHE