Simple (regex) routing in JavaScript

gistfile1.js

module.exports = function router() {
    function router(method, url) {
        var r = get_routes(method), rl = r.length
        for (var i = 0; i < rl; ++i) {
            if (r[i].type == 'string') {
                if (r[i].url == url) 
                    return [[url], r[i].callback] }
            else {
                var route = r[i]
                if (route.type == 'regexp') {
                    var match = route.url.exec(url)
                    if (match)
                        return [match, route.callback] }
                else throw TypeError("unknown routing url type") }}
        return null }
    var routes = { get: [], post: []}
    var get_routes = function(method) { return routes[method] || (routes[method] = []) }
    router.set = function(method, url, callback) {
        get_routes(method).push(
          { url: url
          , callback: callback
          , type: Object.prototype.toString.call(url).slice(8,-1).toLowerCase() })
        return router }
    router.get = function(url, callback) {
        router.set('get', url, callback)
        router.set('head', url, callback)
        return router }
    router.post = function(url, callback) {
        router.set('post', url, callback)
        return router }
    return router }