Fully commented code for the tabs.js script

tabs.js

(function($){
	$.fn.Tabs=function(speed){ /* tabs transition speed parameter */
		return this.each(function(){
			/* define/cache variables */
			var tabs=$(this),
				tabsLabels=tabs.children("ul"),
				tabLabel=tabsLabels.find("a"),
				tabsContent=tabs.children("div"),
				tabLink,
				tabsLoader=tabsContent.children(".ajax-loader"); /* define ajax loader element */
			if(!speed){
				speed=0; /* if speed parameter is not set, defaults to zero */
			}
			/* add tabs content markup if necessary */
			if(tabsContent.length===0){ /* tabs markup does not exist. Create it. */
				tabs.append("<div />");
				tabsContent=tabs.children("div");
				/* no static content exists. Tab content will load via ajax */
				tabsLabels.children("li").each(function(){
					/* apply an ajax class so we can identify later which method
					we're going to use (static or ajax) */
					tabsContent.append("<div class='ajax-tab-content' />"); 
				});
			}else{ /* tabs markup exists */
				tabsContent.children("div").each(function(){
					/* tabs markup exists but it's empty. Tab content will load via ajax */
					if($.trim($(this).text())===""){
						$(this).addClass("ajax-tab-content");
					}
				});
			}
			/* if .ajax-loader doesn't exist and ajax content will be used, create the preloader element */
			if(tabsLoader.length===0 && tabsContent.children("div.ajax-tab-content").length>0){
				tabsContent.append("<span class='ajax-loader' />"); /* create it */
				tabsLoader=tabsContent.children(".ajax-loader"); /* cache it */
			}
			/* if no .active-tab class exists, set the first tab as active */
			if(tabsLabels.find(".active-tab").length===0){
				tabsLabels.children("li:first").addClass("active-tab");
			}
			tabLink=tabsLabels.find(".active-tab a"); /* cache the active tab anchor element */
			tabsContent.css({"height":tabsContent.height()}); /* set the initial height value for animation */
			/* call the LoadTabContent function that loads the tab content
			The first parameter is the returned value of the FindTabContent function
			that finds the target tab content */
			LoadTabContent(FindTabContent(tabLink),tabLink);
			/* tab click event */
			tabLabel.click(function(e){
				e.preventDefault();
				tabLink=$(this); /* store new tabLink value */
				LoadTabContent(FindTabContent(tabLink),tabLink); /* load tab content according to clicked anchor (tabLink) */
			});
			/* function: find tab content from href value or DOM index */
			function FindTabContent(tabLink){ 
				var targetTab,
					tabID=tabLink.attr("href");
				/* check if href attribute exists, its value is not "#" but starts with "#" 
				and a div with an equivalent id exists */
				if(tabID && tabID!="#" && tabID.substring(0)==="#" && tabsContent.find(tabID).length!=0){
					/* find target div based on href value */
					targetTab=tabsContent.find(tabID);
				}else{
					/* find target div based on DOM index */
					tabID=tabLink.parent().index();
					targetTab=tabsContent.children("div").eq(tabID);
				}
				return targetTab;
			}
			/* function: load tab content */
			function LoadTabContent(targetTab,tabLink){
				/* find current active tab label and content */
				var activeTab=tabsLabels.find(".active-tab"),
					activeTabContent=tabsContent.find(".active-tab-content");
				if(activeTabContent.length===0){
					/* if .active-tab-content not found, active tab is the target tab */
					activeTabContent=targetTab;
				}
				activeTabContent.stop().fadeOut(speed,function(){ /* fade-out current active tab */
					activeTab.add(activeTabContent).removeClass("active-tab active-tab-content"); /* remove current active tab */
					tabLink.parent().addClass("active-tab"); /* set active tab */
					/* check if content will be static or loaded via ajax */
					if(targetTab.is(".ajax-tab-content")){ /* ajax content */
						tabsLoader.stop().fadeIn(speed); /* fade-in ajax preloader */
						targetTab.load(tabLink.attr("href"),function(){ /* load the content in targetTab */
							/* make sure all images are fully loaded before revealing tab content */
							var targetTabImages=targetTab.find("img"),
								targetTabImagesLoaded=0;
							if(targetTabImages.length>0){ /* if images exists preload them */
								targetTabImages.bind("load",function(){
									targetTabImagesLoaded++
									/* if final image is fully loaded, fade-out the preloader and 
									show tab content via the ShowTabContent function */
									if(targetTabImagesLoaded>=targetTabImages.length){
										tabsLoader.stop().fadeOut(speed);
										ShowTabContent();
									}
								});
							}else{ /* ajax content without images */
								/* fade-out the preloader and show tab content via the ShowTabContent function */
								tabsLoader.stop().fadeOut(speed);
								ShowTabContent();
							}
						});
					}else{ /* static content */
						ShowTabContent(); /* show tab content via the ShowTabContent function */
					}
					/* function: show tab content */
					function ShowTabContent(){
						/* add .active-tab-content class to the target div and
						set it to block so we can animate its height value. 
						Apply a zero opacity so we can fade it in via $.animate({opacity}) */
						targetTab.addClass("active-tab-content").css({"opacity":0,"display":"block"});
						tabsContent.stop().animate({height:targetTab.outerHeight()},speed,function(){ /* animate wrapper div height */
							targetTab.stop().animate({opacity:1},speed); /* fade-in target tab content */
						});
					}
				});
			}
		});
	}
})(jQuery);