<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style>
#div2 {
width: 150px;
height: 150px;
position: absolute;
background: #CCCCCC;
}
.box{
border: 1px dashed black;
position: absolute;
}
</style>
<script>
window.onload = function() {
var div2 = document.getElementById(‘div2‘);
var x = 0;
var y = 0;
document.onmousedown = function(ev) {
//获取具有兼容性的事件
var oEvent = ev || event;
//x、y分别代表，鼠标与div之间的横坐标和纵坐标
x = oEvent.clientX - div2.offsetLeft;
y = oEvent.clientY - div2.offsetTop;
//创建一个div元素
var box = document.createElement(‘div‘);
//将创建好的样式赋给box
box.className = ‘box‘;
//将div的长宽赋给box
box.style.width = div2.offsetWidth - 2 + ‘px‘;
box.style.height = div2.offsetHeight - 2 + ‘px‘;
//按下鼠标，将div当前的位置赋给box,防止每次点击时，虚线框都会在左上角闪一下
box.style.left = div2.offsetLeft + ‘px‘;
box.style.top = div2.offsetTop + ‘px‘;
//将box插入到页面
document.body.appendChild(box);
//mouseMove函数
document.onmousemove = function(ev) {
var oEvent = ev || event;
//m、n分别代表div的横、纵坐标
var m = oEvent.clientX - x;
var n = oEvent.clientY - y;
//设置div的坐标
box.style.left = m + ‘px‘;
box.style.top = n + ‘px‘;
};
//mouseUp函数
document.onmouseup = function(ev) {
var oEvent = ev || event;
//释放move事件，如果不释放，放开鼠标后，div仍然会跟随鼠标移动
document.onmousemove = null;
document.onmouseup = null;
//放开鼠标后，将虚线框的位置赋给div2
div2.style.left = box.offsetLeft + ‘px‘;
div2.style.top = box.offsetTop + ‘px‘;
//并且移出虚线框
document.body.removeChild(box);
}
return false;
};
};
</script>
</head>
<body>
<div id="div2"></div>
</body>
</html>
原文：http://www.cnblogs.com/youcandomore/p/6780206.html