window.onload = function(){
	createTab();
	hideHeading();
	showCategory('vol4');
	setTabClick('vol4Nav','vol4');
	setTabClick('vol3Nav','vol3');
	setTabClick('vol2Nav','vol2');
	setTabClick('vol1Nav','vol1');
	setTabClick('cdNav','cd');
};

function hide(elementId) {
	document.getElementById(elementId).style.display = "none";
}
function show(elementId) {
	document.getElementById(elementId).style.display = "block";
}
function hideHeading() {
	hide('vol4Heading');
	hide('vol3Heading');
	hide('vol2Heading');
	hide('vol1Heading');
	hide('cdHeading');
}
function showCategory(categoryName){
	hide('vol4'); 
	hide('vol3'); 
	hide('vol2'); 
	hide('vol1'); 
	hide('cd');
	show(categoryName);
	changeTab(categoryName);
}
function createTab() {
	var wrapper = document.getElementById("wrapper");
	var content = document.getElementById("content");
	var nav = document.createElement("ul");
	nav.setAttribute('id','nav');
	nav.appendChild(createListItem('vol4Nav','#vol4','第四楽章'));
	nav.appendChild(createListItem('vol3Nav','#vol3','第三楽章'));
	nav.appendChild(createListItem('vol2Nav','#vol2','第ニ楽章'));
	nav.appendChild(createListItem('vol1Nav','#vol1','第一楽章'));
	nav.appendChild(createListItem('cdNav','#cd','CD情報'));	 
	wrapper.insertBefore(nav,content);
}
function createListItem(id,href,text) {
	var li = document.createElement("li");
	var a = document.createElement("a");
	var t = document.createTextNode(text);
	li.setAttribute('id',id);
	a.setAttribute('href',href);
	a.appendChild(t);
	li.appendChild(a);
	return li;
}
function setTabClick(listName,categoryName) {
	var e = document.getElementById(listName).getElementsByTagName('a')[0];
	e.onclick = function(){
		showCategory(categoryName);
		return false;
	};
}
function changeTab(categoryName){
	var e = document.getElementById('nav');
	e.className = categoryName;
}