在做鼠标移入，移除操作是有俩种方式
-
mouseover mouseout 移入/移出
子级会因为冒泡而影响父级的鼠标移入移出操作
onmouseenter onmouseout 移入/移出（子级不会影响父级）
淘宝放大镜实例：
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>无标题文档</title>
<style>
#div1 {
width: 180px;
height: 180px;
overflow: hidden;
position: relative;
}
#div1 span {
width: 100px;
height: 100px;
background: yellow;
opacity: 0.5;
filter: alpha(opacity=50);
position: absolute;
left: 0;
top: 0;
display: none;
}
#mark {
width: 180px;
height: 180px;
background: red;
position: absolute;
left: 0;
top: 0;
opacity: 0;
filter: alpha(opacity=0);
}
#div2 {
width: 500px;
height: 500px;
position: absolute;
left: 250px;
top: 50px;
overflow: hidden;
}
#div2 img {
position: absolute;
left: 0;
top: 0;
}
</style>
<script>
window.onload = function () {
var oDiv = document.getElementById('div1');
var oSpan = oDiv.getElementsByTagName('span')[0];
var oDiv2 = document.getElementById('div2');
var img2 = oDiv2.getElementsByTagName('img')[0];
oDiv.onmouseover = function () {
oSpan.style.display = 'block';
};
oDiv.onmouseout = function () {
oSpan.style.display = 'none';
};
oDiv.onmousemove = function (ev) {
var ev = ev || window.event;
var L = ev.clientX - oDiv.offsetLeft - oSpan.offsetWidth / 2;
var T = ev.clientY - oDiv.offsetTop - oSpan.offsetHeight / 2;
if (L < 0) {
L = 0;
}
else if (L > oDiv.offsetWidth - oSpan.offsetWidth) {
L = oDiv.offsetWidth - oSpan.offsetWidth;
}
if (T < 0) {
T = 0;
}
else if (T > oDiv.offsetHeight - oSpan.offsetHeight) {
T = oDiv.offsetHeight - oSpan.offsetHeight;
}
oSpan.style.left = L + 'px';
oSpan.style.top = T + 'px';
var scaleX = L / (oDiv.offsetWidth - oSpan.offsetWidth);
var scaleY = T / (oDiv.offsetHeight - oSpan.offsetHeight);
img2.style.left = -scaleX * (img2.offsetWidth - oDiv2.offsetWidth) + 'px';
img2.style.top = -scaleY * (img2.offsetHeight - oDiv2.offsetHeight) + 'px';
};
};
</script>
</head>
<body>
<div id="div1">
[站外图片上传中……(2)]
<span></span>
<div id="mark"></div>
</div>
<div id="div2">
[站外图片上传中……(3)]
</div>
</body>
</html>