鼠标拖动DIV元素

div

<div id="dv"></div>

css

 #dv {
   width:100px;
   height:100px;
   background-color:blue;
   border-radius:50%;
   position:absolute;
}

js

//获取元素
   var dv = document.getElementById('dv');
   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';
}