WordPress/wp-includes/js/customize-preview.min.js

!function(a,b){var c,d=wp.customize;c=function(a,b,c){var d;return function(){var e=arguments;c=c||this,clearTimeout(d),d=setTimeout(function(){d=null,a.apply(c,e)},b)}},d.Preview=d.Messenger.extend({initialize:function(a,e){var f=this;d.Messenger.prototype.initialize.call(this,a,e),this.body=b(document.body),this.body.on("click.preview","a",function(a){a.preventDefault(),f.send("scroll",0),f.send("url",b(this).prop("href"))}),this.body.on("submit.preview","form",function(a){a.preventDefault()}),this.window=b(window),this.window.on("scroll.preview",c(function(){f.send("scroll",f.window.scrollTop())},200)),this.bind("scroll",function(a){f.window.scrollTop(a)})}}),b(function(){if(d.settings=window._wpCustomizeSettings,d.settings){var a,c;a=new d.Preview({url:window.location.href,channel:d.settings.channel}),a.bind("settings",function(a){b.each(a,function(a,b){d.has(a)?d(a).set(b):d.create(a,b)})}),a.trigger("settings",d.settings.values),a.bind("setting",function(a){var b;a=a.slice(),(b=d(a.shift()))&&b.set.apply(b,a)}),a.bind("sync",function(c){b.each(c,function(b,c){a.trigger(b,c)}),a.send("synced")}),a.bind("active",function(){d.settings.nonce&&a.send("nonce",d.settings.nonce)}),a.send("ready"),c=b.map(["color","image","position_x","repeat","attachment"],function(a){return"background_"+a}),d.when.apply(d,c).done(function(a,c,d,e,f){var g,h=b(document.body),i=b("head"),j=b("#custom-background-css");g=function(){var g="";h.toggleClass("custom-background",!(!a()&&!c())),a()&&(g+="background-color: "+a()+";"),c()&&(g+='background-image: url("'+c()+'");',g+="background-position: top "+d()+";",g+="background-repeat: "+e()+";",g+="background-attachment: "+f()+";"),j.remove(),j=b('<style type="text/css" id="custom-background-css">body.custom-background { '+g+" }</style>").appendTo(i)},b.each(arguments,function(){this.bind(g)})})}})}(wp,jQuery);