<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta charset="utf-8">
<title>Document</title>
<style>
#box{width: 200px; height: 200px; background-color: #ccc;position: absolute;
left: 400px; top: 200px;}
</style>
</head>
<body>
<p>asdfasdf</p>
<p>asdfasdf</p>
<p>asdfasdf</p>
<p>asdfasdf</p>
<p>asdfasdf</p>
<p>asdfasdf</p>
<p>asdfasdf</p>
<p>asdfasdf</p>
<p>asdfasdf</p>
<p>asdfasdf</p>
<p>asdfasdf</p>
<p>asdfasdf</p>
<p>asdfasdf</p>
<p>asdfasdf</p>
<p>asdfasdf</p>
<p>asdfasdf</p>
<p>asdfasdf</p>
<p>asdfasdf</p>
<p>asdfasdf</p>
<p>asdfasdf</p>
<p>asdfasdf</p>
<p>asdfasdf</p>
<p>asdfasdf</p>
<div id="box"></div>
<script>
var oDiv = document.getElementById('box');
oDiv.onmousedown = function(ev){
var oEvent = ev || event;
//xy - 算鼠标距离元素的位置
var x = oEvent.clientX - oDiv.getBoundingClientRect().left,
y = oEvent.clientY - oDiv.getBoundingClientRect().top;
document.onmousemove = function(ev){
var oEvent = ev || event;
//物体要移动的位置
var l = oEvent.clientX - x,
t = oEvent.clientY - y;
// console.log(l);
if(l<=0) l=0;
if(t<=0) t=0;
if(l>=document.documentElement.clientWidth - oDiv.offsetWidth) l=document.documentElement.clientWidth - oDiv.offsetWidth;
if(t>=document.documentElement.clientHeight - oDiv.offsetHeight) t=document.documentElement.clientHeight - oDiv.offsetHeight;
oDiv.style.left = l + 'px';
oDiv.style.top = t + 'px';
}
oDiv.onmouseup = function(){
if(oDiv.releaseCapture) oDiv.releaseCapture();
document.onmousemove = null;
}
if(oDiv.setCapture) oDiv.setCapture();
return false;
}
</script>
</body>
</html>
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