[added] renderComponentToString()

closes #36

modules/Router.js

@@ -208,6 +208,25 @@ mergeProperties(Router.prototype, {
     return component;
   },
 
+  /**
+   * Renders this Router's component as a string. Since this may be an asynchronous
+   * process, this returns a Promise.
+   */
+  renderComponentToString: function(path) {
+    invariant(
+      !this.state.props,
+      'You may only call renderComponentToString() on a new Router'
+    );
+
+    return this.dispatch(path).then(function() {
+      var route = this.route;
+      var state = this.state;
+      var descriptor = route.handler(state.props);
+      var markup = React.renderComponentToString(descriptor);
+      return markup;
+    }.bind(this));
+  },
+
   handleRouteChange: function () {
     this.dispatch(URLStore.getCurrentPath());
   }

specs/Router.spec.js

@@ -1,4 +1,5 @@
 require('./helper');
+var Promise = require('es6-promise').Promise;
 var Router = require('../modules/Router');
 var RouteComponent = require('../modules/components/Route');
 
@@ -125,6 +126,45 @@ describe('a Router with custom props', function() {
   });
 });
 
+describe('a Router that renders on the server', function() {
+  it('works with async willTransitionTo()', function(done) {
+    var dataStore = 'goodbye';
+    var Layout = React.createClass({
+      render: function() {
+        return React.DOM.article(null, this.props.activeRoute);
+      }
+    });
+    var AsyncApp = React.createClass({
+      displayName: 'AsyncApp',
+      statics: {
+        willTransitionTo: function() {
+          return new Promise(function(resolve) {
+            setTimeout(function() {
+              dataStore = 'hello';
+              resolve();
+            }, 0);
+          });
+        }
+      },
+      render: function() {
+        return React.DOM.div(null, dataStore);
+      }
+    });
+
+    var router = Router(
+      RouteComponent({ path: '/', handler: Layout},
+        RouteComponent({ path: '/a', handler: AsyncApp }))
+    );
+
+    router.renderComponentToString('/a').then(function(result) {
+      expect(result.indexOf('div') > -1).toBe(true);
+      expect(result.indexOf('hello') > -1).toBe(true);
+
+      done();
+    });
+  });
+});
+
 function lastItem(array) {
   return array[array.length - 1];
 }