Theme Customizer: Maintain scrolled position when preview performs a full refresh. Allow wp.customize.Messenger to send/receive falsy values. see #19910.

git-svn-id: http://core.svn.wordpress.org/trunk@20745 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/js/customize-base.dev.js

@@ -469,14 +469,14 @@ if ( typeof wp === 'undefined' )
 
 			message = JSON.parse( event.data );
 
-			if ( message && message.id && message.data && this.topics[ message.id ] )
+			if ( message && message.id && typeof message.data !== 'undefined' && this.topics[ message.id ] )
 				this.topics[ message.id ].fireWith( this, [ message.data ]);
 		},
 
 		send: function( id, data ) {
 			var message;
 
-			data = data || {};
+			data = typeof data === 'undefined' ? {} : data;
 
 			if ( ! this.url() )
 				return;

wp-includes/js/customize-controls.dev.js

@@ -311,6 +311,11 @@
 
 			api.Messenger.prototype.initialize.call( this, params.url );
 
+			this.scroll = 0;
+			this.bind( 'scroll', function( distance ) {
+				this.scroll = distance;
+			});
+
 			// We're dynamically generating the iframe, so the origin is set
 			// to the current window's location, not the url's.
 			this.origin.unlink( this.url ).set( window.location.href );
@@ -335,10 +340,12 @@
 		loaded: function() {
 			if ( this.iframe )
 				this.iframe.remove();
+
 			this.iframe = this.loading;
 			delete this.loading;
 
 			this.targetWindow( this.iframe[0].contentWindow );
+			this.send( 'scroll', this.scroll );
 		},
 		query: function() {},
 		refresh: function() {

wp-includes/js/customize-preview.dev.js

@@ -1,5 +1,21 @@
 (function( exports, $ ){
-	var api = wp.customize;
+	var api = wp.customize,
+		debounce;
+
+	debounce = function( fn, delay, context ) {
+		var timeout;
+		return function() {
+			var args = arguments;
+
+			context = context || this;
+
+			clearTimeout( timeout );
+			timeout = setTimeout( function() {
+				timeout = null;
+				fn.apply( context, args );
+			}, delay );
+		};
+	};
 
 	api.Preview = api.Messenger.extend({
 		/**
@@ -27,6 +43,15 @@
 			this.body.on( 'submit.preview', 'form', function( event ) {
 				event.preventDefault();
 			});
+
+			this.window = $( window );
+			this.window.on( 'scroll.preview', debounce( function() {
+				self.send( 'scroll', self.window.scrollTop() );
+			}, 200 ));
+
+			this.bind( 'scroll', function( distance ) {
+				self.window.scrollTop( distance );
+			});
 		}
 	});