Writing a "url_for" helper for Express

examples-and-issues.js

// What name can I refer to ?
app.get('/hello-world', function () { console.log(3); });

// OK, suppose I can build the path from params
app.get('/:id/:name', function hello1 () { console.log(1); });

// OK, suppose the "callback" is the last one
app.get('/hello/:name', requiresAuthentication, function hello2 () { console.log(2); });

// How do I build the path ?
app.get(/\/hi\/([a-z]+)/, function hello3 () { console.log(3); });




// Expected example
console.log(app.url_for('hello1', {"id": 42, "name": "dude", "p1": 33, "p2": "some additional param"}));
// /42/dude?p1=33&p2=some%20additional%20param

impl.js

app.url_for = function url_for (route, params) {
  params = params || {};
  var url = null, url_params = {};
  for (var i=0; i<this.routes.routes.get.length; i++) {
    var a_route = this.routes.routes.get[i];
    var callback = a_route.callbacks[a_route.callbacks.length-1];
    if (callback.name === route) {
      url = a_route.path;
      if (a_route.keys) {
        for (var j=0; j<a_route.keys.length; j++) {
          var key = a_route.keys[j];
          if (!key.optional && 'undefined' === typeof params[key.name]) {
            throw new Error('Missing parameter "' + key.name + '" for route "' + route + '"');
          }
          var value = params[key.name] || null;
          if (value !== null) {
            url_params[key.name] = value;
          }
        }
      }
      break;
    }
  }
  if (url === null) {
    url = route;
  }
  if (!url.match(/^\//)) {
    throw new Error('Invalid URL: no trailing slash');
  }
  for (var missing_param in params) {
    if ('undefined' == typeof url_params[missing_param]) {
      url_params[missing_param] = params[missing_param];
    }
  }
  for (var name in url_params) {
    if (~url.search(':' + name)) {
      url = url.replace(':' + name, encodeURIComponent(url_params[name]));
    } else {
      if (~url.search(/\?/)) {
        url += '&';
      } else {
        url += '?';
      }
      url += encodeURIComponent(name) + '=' + encodeURIComponent(url_params[name]);
    }
  }
  return url;
};