首先先看实现代码
html代码部分
<!DOCTYPE html> <html> <head> <title>Previewing Links</title> <link rel="stylesheet"href="script05.css" rel="external nofollow" > <script src="script05.js"></script> </head> <body> <h2>A Gentle Introduction to JavaScript</h2> <ul> <li><a href="jsintro/2000-08.html" rel="external nofollow" >August column</a></li> <li><a href="jsintro/2000-09.html" rel="external nofollow" >September column</a></li> <li><a href="jsintro/2000-10.html" rel="external nofollow" >October column</a></li> <li><a href="jsintro/2000-11.html" rel="external nofollow" >November column</a></li> </ul> <div id="previewWin"> </div> </body> </html>
这个CSS设置预览弹出窗口的样式
#previewWin {
background-color: #FF9;
width: 400px;
height: 100px;
font: .8em arial, helvetica, sans-serif;
padding: 5px;
position: absolute;
visibility: hidden;
top: 10px;
left: 10px;
border: 1px #CC0 solid;
clip: auto;
overflow: hidden;
}
#previewWin h1, #previewWin h2 {
font-size: 1.0em;
}
这个JavaScript进行服务器请求并且显示弹出窗口
window.onload = initAll;
var xhr = false;
var xPos, yPos;
function initAll() {
var allLinks = document.getElementsByTagName("a");
for (var i=0; i< allLinks.length; i++) {
allLinks[i].onmouseover = getPreview;
}
}
function getPreview(evt) {
if (evt) {
var url = evt.target;
}
else {
evt = window.event;
var url = evt.srcElement;
}
xPos = parseInt(evt.clientX);
yPos = parseInt(evt.clientY);
if (window.XMLHttpRequest) {
xhr = new XMLHttpRequest();
}
else {
if (window.ActiveXObject) {
try {
xhr = new ActiveXObject("Microsoft.XMLHTTP");
}
catch (e) { }
}
}
if (xhr) {
xhr.onreadystatechange = showContents;
xhr.open("GET", url, true);
xhr.send(null);
}
else {
alert("Sorry, but I couldn't create an XMLHttpRequest");
}
}
function hidePreview() {
document.getElementById("previewWin").style.visibility = "hidden";
}
function showContents() {
var prevWin = document.getElementById("previewWin");
if (xhr.readyState == 4) {
if (xhr.status == 200) {
prevWin.innerHTML = xhr.responseText;
}
else {
prevWin.innerHTML = "There was a problem with the request " + xhr.status;
}
prevWin.style.top = yPos+2 + "px";
prevWin.style.left = xPos+2 + "px";
prevWin.style.visibility = "visible";
prevWin.onmouseout = hidePreview;
}
}
分析：
1.
var allLinks = document.getElementsByTagName("a");
for (var i=0; i< allLinks.length;i++) {
allLinks[i].onmouseover = getPreview;
}
这是initAll()函数的内容，它遍历页面上的所有链接，并且在每个链接上添加onmouseover事件
处理程序。这个事件处理程序将（你下面将看到的）读取目标页面并且向（可能的）访问者显示预览。
