basic router in typescript

router.ts

export type Route = {
  method: "*" | "GET" | "POST" | "PUT" | "PATCH" | "DELETE" | "HEAD" | "OPTIONS" | "CONNECT" | "TRACE"
  path: string
  regexp: RegExp
  handler: (request: Request, route: MatchedRoute) => Promise<Response>
}

export type MatchedRoute = Route & {
  url: URL
}

// excellent regex from kwhitely/itty-router
// it takes a path and turns it into a regex for later matching
function pathToRegexp(path: string): RegExp {
  return RegExp(`^${path
    .replace(/(\/?)\*/g, '($1.*)?')                             // trailing wildcard
    .replace(/(\/$)|((?<=\/)\/)/, '')                           // remove trailing slash or double slash from joins
    .replace(/(:(\w+)\+)/, '(?<$2>.*)')                         // greedy params
    .replace(/:(\w+)(\?)?(\.)?/g, '$2(?<$1>[^/]+)$2$3')         // named params
    .replace(/\.(?=[\w(])/, '\\.')                              // dot in path
    .replace(/\)\.\?\(([^\[]+)\[\^/g, '?)\\.?($1(?<=\\.)[^\\.')  // optional image format
  }/*$`)
}

export class Router {
  routes: Route[] = []

  add(method: Route["method"], path: Route["path"], handler: Route["handler"]) {
    this.routes.push({
      method,
      path,
      handler,
      regexp: pathToRegexp(path)
    })
  }

  match(request: Request, url: URL): Route | undefined {
    return this.routes
      .filter(route => route.method === request.method || route.method === "*")
      .find(route => route.regexp.test(url.pathname))
  }

  async handle(request: Request): Promise<Response> {
    let response, match, url = new URL(request.url)
    const route = this.match(request, url)
    if (route) {
      return route.handler(request, {...route, url})
    } else {
      return new Response(null, { status: 404 })
    }
  }
}

// Use it like...

const router = new Router()

router.add("GET", "/users/:username", async (request, route) => {
	console.log(route.regexp, route.url.pathname)
	const username = route.regexp.exec(route.url.pathname)?.groups?.username
	return new Response(`Matched ${route.path}, Hello ${username}!`)
})

router.add("POST", "/users", async (request, route) => {
	const fd = await request.formData()
	return new Response(`Matched ${route.path}:\n${JSON.stringify(Array.from(fd.entries()))}`)
})

router.add("*", "/foo", async (request, route) => {
	return new Response("FOooooo!")
})

// then somewhere where you have a request...
router.handle(request)