网上遇到一个div拖动的例子，仅支持拖动不能改变大小，
有需要改变大小可以参考另外一篇文章：https://blog.csdn.net/vtopqx/article/details/89066771
拖动代码如下：
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>JS拖拽div/title>
<script src="https://libs.baidu.com/jquery/1.11.3/jquery.min.js"></script>
<style>
#dv {
width:100px;
height:100px;
background-color:blue;
position:absolute;
}
</style>
</head>
<body>
<div id="test">
<div id="dv" class="list">0000</div>
</div>
<script>
//获取元素
var divId = 'dv';
var dv = document.getElementById(divId);
var x = 0;
var y = 0;
var l = 0;
var t = 0;
var isDown = false;
//鼠标按下事件
dv.onmousedown = function(e) {
//获取x坐标和y坐标
x = e.clientX;
y = e.clientY;
//获取左部和顶部的偏移量
l = dv.offsetLeft;
t = dv.offsetTop;
//开关打开
isDown = true;
//设置样式
dv.style.cursor = 'move';
}
//鼠标移动
window.onmousemove = function(e) {
if (isDown == false) {
return;
}
//获取x和y
var nx = e.clientX;
var ny = e.clientY;
//计算移动后的左偏移量和顶部的偏移量
var nl = nx - (x - l);
var nt = ny - (y - t);
dv.style.left = nl + 'px';
dv.style.top = nt + 'px';
}
//鼠标抬起事件
dv.onmouseup = function() {
//开关关闭
isDown = false;
dv.style.cursor = 'default';
}
</script>
</body>
</html>
