- 因为上个版本中的图片占位区和文字占位区完全是给showPic脚本服务的，所以这里在JS脚本里用DOM的create系列方法把结构和行为彻底分开
- DOM中提供了insertBefore方法，但没有inserAfter，因为这里占位区是在ul之后，所以我们这里手写这个方法。
- 注意innerHTML方法和create方法,appendChild方法的区别，innerHTML是不管元素节点里面有没有HTML内容，里面的全部内容都将替换成innerHTML的内容，当然比较方便，如果想对插入的内容进行处理，还需要DOM提供的那些精确地方法和属性。innerHTML也是HTML专有属性，不能用于任何其他标记语言文档。
- 共享onload事件原理：将原来的load事件进行备份如果之前没有监听，则直接将此函数设为监听函数，如果已设置，则设为一个新的函数，这个新的函数被触发后，会先后触发原来的监听函数和你要设置的监听函数。这样就实现了onload加载的一个事件队列。保证了监听函数都是在onload加载之后，也就是页面加载完毕时执行函数，即document文档形成之后执行函数。（网页加载完毕时会触发一个onload事件）
剩下的就是代码了：
showPic.js:
function addLoadEvent(func) {
var oldonload = window.onload;
if (typeof window.onload != 'function') {
window.onload = func;
} else {
window.onload = function() {
oldonload();
func();
}
}
}
function insertAfter(newElement,targetElement) {
var parent = targetElement.parentNode;
if (parent.lastChild == targetElement) {
parent.appendChild(newElement);
} else {
parent.insertBefore(newElement,targetElement.nextSibling);
}
}
function preparePlaceholder() {
if (!document.createElement) return false;
if (!document.createTextNode) return false;
if (!document.getElementById) return false;
if (!document.getElementById("imagegallery")) return false;
var placeholder = document.createElement("img");
placeholder.setAttribute("id","placeholder");
placeholder.setAttribute("src","images/placeholder.gif");
placeholder.setAttribute("alt","my image gallery");
var description = document.createElement("p");
description.setAttribute("id","description");
var desctext = document.createTextNode("Choose an image");
description.appendChild(desctext);
var gallery = document.getElementById("imagegallery");
insertAfter(placeholder,gallery);
insertAfter(description,placeholder);
}
function prepareGallery() {
if (!document.getElementsByTagName) return false;
if (!document.getElementById) return false;
if (!document.getElementById("imagegallery")) return false;
var gallery = document.getElementById("imagegallery");
var links = gallery.getElementsByTagName("a");
for ( var i=0; i < links.length; i++) {
links[i].onclick = function() {
return showPic(this);
}
links[i].onkeypress = links[i].onclick;
}
}
function showPic(whichpic) {
if (!document.getElementById("placeholder")) return true;
var source = whichpic.getAttribute("href");
var placeholder = document.getElementById("placeholder");
placeholder.setAttribute("src",source);
if (!document.getElementById("description")) return false;
if (whichpic.getAttribute("title")) {
var text = whichpic.getAttribute("title");
} else {
var text = "";
}
var description = document.getElementById("description");
if (description.firstChild.nodeType == 3) {
description.firstChild.nodeValue = text;
}
return false;
}
addLoadEvent(preparePlaceholder);
addLoadEvent(prepareGallery);
gallery.html:
<!DOCTYPE html>
<html lang="en">
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<title>Image Gallery</title>
<script type="text/javascript" src="scripts/showPic.js"></script>
<link rel="stylesheet" href="styles/layout.css" type="text/css" media="screen" />
</head>
<body>
<h1>Snapshots</h1>
<ul id="imagegallery">
<li>
<a href="images/fireworks.jpg" title="A fireworks display">
<img src="images/thumbnail_fireworks.jpg" alt="Fireworks" />
</a>
</li>
<li>
<a href="images/coffee.jpg" title="A cup of black coffee" >
<img src="images/thumbnail_coffee.jpg" alt="Coffee" />
</a>
</li>
<li>
<a href="images/rose.jpg" title="A red, red rose">
<img src="images/thumbnail_rose.jpg" alt="Rose" />
</a>
</li>
<li>
<a href="images/bigben.jpg" title="The famous clock">
<img src="images/thumbnail_bigben.jpg" alt="Big Ben" />
</a>
</li>
</ul>
</body>
</html>
layout.css:
body {
font-family: "Helvetica","Arial",serif;
color: #333;
background-color: #ccc;
margin: 1em 10%;
}
h1 {
color: #333;
background-color: transparent;
}
a {
color: #c60;
background-color: transparent;
font-weight: bold;
text-decoration: none;
}
ul {
padding: 0;
}
li {
float: left;
padding: 1em;
list-style: none;
}
#imagegallery {
list-style: none;
}
#imagegallery li {
display: inline;
}
#imagegallery li a img {
border: 0;
}