customize-preview.js

(function( exports, $ ){
	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({
		/**
		 * Requires params:
		 *  - url    - the URL of preview frame
		 */
		initialize: function( params, options ) {
			var self = this;

			api.Messenger.prototype.initialize.call( this, params, options );

			this.body = $( document.body );
			this.body.on( 'click.preview', 'a', function( event ) {
				event.preventDefault();
				self.send( 'scroll', 0 );
				self.send( 'url', $(this).prop('href') );
			});

			// You cannot submit forms.
			// @todo: Allow form submissions by mixing $_POST data with the customize setting $_POST data.
			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 );
			});
		}
	});

	$( function() {
		api.settings = window._wpCustomizeSettings;
		if ( ! api.settings )
			return;

		var preview, bg;

		preview = new api.Preview({
			url: window.location.href,
			channel: api.settings.channel
		});

		preview.bind( 'settings', function( values ) {
			$.each( values, function( id, value ) {
				if ( api.has( id ) )
					api( id ).set( value );
				else