Revert "Revert "Simplify arities of setPath/navigate(). Fixes STRML#81.""

This reverts commit 345c070.

Author: 7rulnik

lib/RouterMixin.js

@@ -137,11 +137,6 @@ var RouterMixin = {
    * @param {Callback} cb
    */
   navigate: function(path, navigation, cb) {
-    if (typeof navigation === 'function' && cb === undefined) {
-      cb = navigation;
-      navigation = {};
-    }
-    navigation = navigation || {};
     path = join(this.state.prefix, path);
     this.getEnvironment().setPath(path, navigation, cb);
   },

lib/environment/DummyEnvironment.js

@@ -17,7 +17,12 @@ DummyEnvironment.prototype.constructor = DummyEnvironment;
 
 DummyEnvironment.prototype.getPath = emptyFunction.thatReturnsNull;
 
-DummyEnvironment.prototype.setPath = function(path, cb) {
+DummyEnvironment.prototype.setPath = function(path, navigation, cb) {
+  // Support old (path, cb) arity
+  if (typeof navigation === 'function' && cb === undefined) {
+    cb = navigation;
+    navigation = {};
+  }
   this.path = path;
   cb();
 };

lib/environment/Environment.js

@@ -44,14 +44,18 @@ Environment.prototype.makeHref = function makeHref(path) {
 }
 
 Environment.prototype.navigate = function navigate(path, navigation, cb) {
+  return this.setPath(path, navigation, cb);
+}
+
+Environment.prototype.setPath = function(path, navigation, cb) {
+  // Support (path, cb) arity.
   if (typeof navigation === 'function' && cb === undefined) {
     cb = navigation;
     navigation = {};
   }
-  return this.setPath(path, navigation, cb);
-}
+  // Support (path) arity.
+  if (!navigation) navigation = {};
 
-Environment.prototype.setPath = function(path, navigation, cb) {
   if (!navigation.isPopState) {
     if (navigation.replace) {
       this.replaceState(path, navigation);