1.兼容getElementsByClassName
function getElementByClassName(node,classname){
if(node.getElementsByClassName){
//使用现有的方法
return node.getElementsByClassName(classname);
} else {
var results=new Array();
var elems = node.getElementsByTagName("*");
for(var i=0;i<elems.length;i++){
if(elems[i].className.indexOf(classname) != -1){
results[results.length] = elems[i];
}
}
}
}
2.获取属性getAttribute,getAttribute
var shopping=document.getElementById("purchases");
alert(shopping.getAttribute("title"));
shopping.setAttribute("title","a list of goods");
alert(shopping.getAttribute("title"));
3.value 和 src
//下面两个等价
element.value="new value";
element.setAttribute("value","new value");
element.src="href";
element.setAttribute("src","new value");
4.childNodes
用下面语法获取节点的nodeType属性
node.nodeType
//nodeType属性共有12种可取值，但其中仅有3种有价值
1.元素节点的nodeType 属性值为1
2.属性节点的nodeType 属性值为2
3.文本节点的nodeType 属性值为3
```
如果想获得一个文本节点的值
```
node.nodeValue;
```
获取第一个和最后一个节点
```
node.firstChild == node.childNodes[0]
node.lastChild == node.childNodes[node.childNodes.length-1]
```
具体应用，动态切换图片
```
function showPic(whichpic) {
var source = whichpic.getAttribute("href");
var placeholder = document.getElementById("placeholder");
placeholder.setAttribute("src",source);
var text = whichpic.getAttribute("title");
var description = document.getElementById("description");
description.firstChild.nodeValue = text;
}
<a href="images/fireworks.jpg" title="A fireworks display"
onclick="showPic(this); return false;">
Fireworks
</a>
<img id="placeholder" src="images/placeholder.gif" alt="my image gallery" />
```
####5.一个平稳退化的例子
```
<!DOCTYPE html>
<html lang="en">
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<title>Example</title>
<script type="text/JavaScript">
window.onload = function() {
if (!document.getElementsByTagName) return false;
var lnks = document.getElementsByTagName("a");
for (var i=0; i<lnks.length; i++) {
if (lnks[i].getAttribute("class") == "popup") {
lnks[i].onclick = function() {
popUp(this.getAttribute("href"));
return false;
}
}
}
}
function popUp(winURL) {
window.open(winURL,"popup","width=320,height=480");
}
</script>
</head>
<body>
//样式分离，并没有增加什么js代码
//<a href="http://www.example.com/" onclick="popUp(this.href);return false;">Example</a>
<a href="http://www.example.com/" class="popup">Example</a>
</body>
</html>
```
####6.图片库代码改进
```
//点击事件处理函数
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;
//判断title属性是否存在
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;//不让浏览器执行默认行为
}
//为连接增加点击事件，一个函数只有一个出口并集中在开头位置
function prepareGallery() {
if (!document.getElementsByTagName) return false;
if (!document.getElementById) return false;
//预防性措施
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);
}
//最好不使用，因为onclick也支持按键
// links[i].onkeypress = links[i].onclick;
}
}
//共享onload事件
function addLoadEvent(func) {
var oldonload = window.onload;
if (typeof window.onload != 'function') {
window.onload = func;
} else {
window.onload = function() {
oldonload();
func();
}
}
}
addLoadEvent(prepareGallery);
```
```
<!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>
<img id="placeholder" src="images/placeholder.gif" alt="my image gallery" />
<p id="description">Choose an image.</p>
</body>
</html>
```
####7.动态创建标记
传统方法，没有做到样式和行为分离,不推荐
```
<script type="text/javascript">
document.write("<p>This is inserted.</p>");
</script>
```
把一大段html放入文档中innerHTML
```
var testdiv = document.getElementById("testdiv");
testdiv.innerHTML="<p>I inserted <em>this</em> content.</p>";
```
#####dom方法
用到的这几个方法或者属性
parentNode 属性
lastChild 属性
appendChild 方法
insertBefore 方法
nextSibling 属性
```
window.onload = function() {
var para = document.createElement("p");
var txt1 = document.createTextNode("I inserted ");
var emphasis = document.createElement("em");
var txt2 = document.createTextNode("this");
var txt3 = document.createTextNode(" content.");
para.appendChild(txt1);
emphasis.appendChild(txt2);
para.appendChild(emphasis);
para.appendChild(txt3);
var testdiv = document.getElementById("testdiv");
testdiv.appendChild(para);
}
```
图片库代码，刚开始展示的文字和图片用js生成
#####注意插入之前gallery.parentNode.insertBefore(placeholder,gallery);
#####没有insertAfter
```
function preparePlaceholder() {
if (!document.createElement) return false;
if (!document.createTextNode) 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");
gallery.parentNode.insertBefore(placeholder,gallery);
gallery.parentNode.insertBefore(description,gallery);
}
```
自己实现一个insertAfter
```
function insertAfter(newElement,targetElement) {
var parent = targetElement.parentNode;
if (parent.lastChild == targetElement) {
parent.appendChild(newElement);
} else {
parent.insertBefore(newElement,targetElement.nextSibling);
}
}
```