JavaScript 拖拽事件

<!DOCTYPE html>
<html lang="zh">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>拖拽事件</title>
    <style>
 .nav {
  height: 50px;
  width: 100%;
  background-color: #b1ffe5;
}

#box {
  width: 400px;
  height: 300px;
  border: 5px solid #eee;
  box-shadow: 2px 2px 2px 2px #666;
  position: absolute;
  top: 40%;
  left: 40%;
  background-color: white;
  cursor: move;


  /*不让文字被选中*/
  -webkit-user-select:none;
        -moz-user-select:none;
        -ms-user-select:none;
        user-select:none;


}

#drop {
  width: 100%;
  height: 35px;
  background-color: #7c9299;
  border-bottom: 1px solid #369;
  line-height: 35px;
  color: white;
  cursor: move;
}

#close {
  float: right;
  cursor: pointer;
}

* {
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  user-select: none;
}


    </style>
</head>
<body>

    <div class="nav">
        <a href="javascript:;" id="re">注册信息</a>
    </div>

    <div  id="box">

        <div  id="drop">可拖拽这里移动窗口位置
            <span id="close" >关闭窗口</span>
        </div>

        <div class="bd"></div>

    </div>



<script>
    //获取元素
    var box = document.getElementById("box");
    var drop = document.getElementById("drop");
    var close = document.getElementById("close");


    //给drop添加鼠标按下事件，在内部继续绑定一个鼠标移动事件
    drop.onmousedown = function(e){
            e = e || window.event;
        //记忆鼠标按下时，鼠标在父盒子内部的间距
            var l = e.pageX - box.offsetLeft;
            var t = e.pageY - box.offsetTop;

        drop.onmousemove = function(e){
            e = e || window.event;
         
                //鼠标移动过程中，可以计算box的left和top
                var nowleft = e.pageX - l;
                var nowtop = e.pageY - t;
            
                box.style.left = nowleft + "px";
                box.style.top = nowtop + "px";

        };
    };






//鼠标弹起事件
drop.onmouseup = function(){
    drop.onmousemove = null;
};




//点击关闭box
close.onclick = function(){
    box.style.display = "none";
};


</script>

</body>
</html>