A javascript router.

router.js

/*
  Router.

  Unlike larger projects (crossroads-min.js ~6.8kb, davis-min.js ~10kb, ...)
  this router <1kb is intended to do one thing well; route. No events,
  listeners, loggers, history or any other bullshit just a way to execute
  callbacks by path.

  @example
    // document.location.pathname #=> /posts/media/2
    var router = new Router;
    router.on('/posts/{type}/{id}', function (params) {
      console.warn(params); #=> {type: 'media', id: '2'}
    });
  @todo Optional regexp in capture group.
    {name:a-z0-9+} see http://gorilla-web.appspot.com/pkg/pat
  @note Requires underscore.js >= 1.4.0 (Sep 27, 2012)
*/
window.Router = (function () {
  var Route = function (path, callback) {
    var names = [];
    re = path.replace(/((\{\w+\})|[-[\]()*+?.,\\^$|#])/g, function (matches, c, capture) {
      if (c == '*') {
        names.push('splat');
        return '(.*?)';
      }
      else if (c.match(/[-[\]()+?.,\\^$|#]/)) {
        return '\\' + c;
      }
      else if (match = /^\{(\w+)}$/.exec(capture)) {
        names.push(match[1]);
        return '([^/?#]+)';
      }
      else {
        // TODO: Something has gone badly wrong.
      }
    });

    this._regexp   = new RegExp('^' + re + '$');
    this._names    = names;
    this._callback = callback;
  };

  function build_params (names, captures) {
    var name, value, counts = _.countBy(names, function (name) { return name });
    return _.reduce(_.zip(names, captures), function (params, param) {
      name = param[0], value = param[1];
      if (counts[name] > 1) {
        if (!params[name]) params[name] = [];
        params[name].push(value);
      }
      else {
        params[name] = value;
      }
      return params;
    }, {});
  }

  Route.prototype = {
    test: function (path) {
      if (captures = this._regexp.exec(path)) {
        this._callback(build_params(this._names, captures.slice(1)));
      }
    }
  };

  var Router = function () {
    this.routes = [];
  };

  Router.prototype = {
    on: function (path, callback) {
      this.routes.push(new Route(path, callback));
    },
    route: function () {
      _.each(this.routes, function (route) { route.test(document.location.pathname) });
    },
    start: function () {
      var router = this;

      // Avoid popstate on load chrome bug.
      // http://code.google.com/p/chromium/issues/detail?id=63040#c11
      router.route();
      window.addEventListener('load', function () {
        setTimeout(function () {
          window.addEventListener('popstate', _.bind(router.route, router));
        }, 0);
      });
    }
  };

  return Router;
})();