Rework menu navigation: these changes build off pull request #239 for issue #200

* Only set button and menu if container is not null.
 * Break up the "return early" conditional into multiple parts.
 * Shorten the name of the toggled class from `toggled-on` to `toggled`.
 * Restore the "Hide menu toggle button if menu is empty." documentation.
 * Remove the `nav-menu` class. The previous code would replace any custom custom classes applied via `wp_nav_menu()` or template file.
 * Replace the `nav-menu` selector is style.css with selectors that will target both a custom nav menu and a page menu. These changes could use critical feedback. Do you know of an edge case where they might not work as expected?

js/navigation.js

@@ -5,28 +5,28 @@
  */
 ( function() {
 	var container = document.getElementById( 'site-navigation' ),
-	    button    = container.getElementsByTagName( 'h1' )[0],
+		button,
+		menu;
+
+	if ( ! container )
+		return;
+
+	button = container.getElementsByTagName( 'h1' )[0];
+	if ( 'undefined' == typeof button )
+		return;
+
 	menu = container.getElementsByTagName( 'ul' )[0];
 
-	if ( undefined == button || undefined == menu )
+	// Hide menu toggle button if menu is empty and return early.
-		return false;
+	if ( 'undefined' == typeof menu ) {
+		button.style.display = 'none';
+		return;
+	}
 
 	button.onclick = function() {
-		if ( -1 == menu.className.indexOf( 'nav-menu' ) )
+		if ( -1 != container.className.indexOf( 'toggled' ) )
-			menu.className = 'nav-menu';
+			container.className = container.className.replace( ' toggled', '' );
-
+		else
-		if ( -1 != button.className.indexOf( 'toggled-on' ) ) {
+			container.className += ' toggled';
-			button.className = button.className.replace( ' toggled-on', '' );
-			menu.className = menu.className.replace( ' toggled-on', '' );
-			container.className = container.className.replace( 'main-small-navigation', 'navigation-main' );
-		} else {
-			button.className += ' toggled-on';
-			menu.className += ' toggled-on';
-			container.className = container.className.replace( 'navigation-main', 'main-small-navigation' );
-		}
 	};
-
-	// Hide menu toggle button if menu is empty.
-	if ( ! menu.childNodes.length )
-		button.style.display = 'none';
 } )();

style.css

@@ -447,7 +447,8 @@ a:active {
 
 @media screen and (max-width: 600px) {
 	.menu-toggle,
-	.main-small-navigation ul.nav-menu.toggled-on {
+	.navigation-main.toggled ul.menu,
+	.navigation-main.toggled div.menu > ul {
 		display: block;
 	}
 
@@ -456,6 +457,7 @@ a:active {
 	}
 }
 
+
 /* =Content
 ----------------------------------------------- */