原生JS可拖动弹窗效果实例代码

这个代码不是我原创的，只是最近想学自己做一个很漂亮的弹窗，自己本来是不会怎么写的，所以上网去找了下，感觉这个不错，很简单，很实用，入门很棒。我就改了下，使逻辑性和可读性更好。

　　原作者已不可考。感谢原作者，阿门。

代码如下:

<html>
    <head>
        <meta http-equiv="Content-Type"content="text/html; charset=gb2312"/>
        <meta name="author" content="www.newxing.com" />
        <meta name="author email" content="123@linhaibo.com" />
        <title>弹出窗口登录效果</title>
        <style>
   body,#Mdown {
    margin: 0;
    padding: 0;
    text-align: center;
    font: normal 14px/180% Tahoma,sans-serif;
   }
   #loginBox {
    margin: 0 auto;
    padding: 0px;
    text-align: left;
    width: 280px;
    height: 150px;
    background: #EAEEFF;
    font-size: 9pt;
    border: 1px solid #829AFF;
    overflow: hidden;
    filter: alpha(opacity=90);
    opacity: 1;
   }
   #loginBox .title {
    text-align: left;
    padding-left: 10px;
    font-size: 11pt;
    border-bottom: 1px solid #829AFF;
    height: 25px;
    line-height: 25px;
    cursor: move;
   }
   #loginBox .t1 {
    float: left;
    font-weight: bold;
    color: #AA7B7B;
    text-decoration: none;
   }
   #loginBox .t2 {
    float: right;
    text-align: center;
    line-height: 18px;
    height: 18px;
    width: 18px;
    margin-top: 3px;
    margin-right: 2px;
    overflow: hidden;
    border: 1px solid #FF5889;
    background: #FFE0E9;
    cursor: pointer;
   }
   #loginBox .login {
    text-align: center;
    width: 100%;
    height: 100%;
   }
   input.submit {
    float: right;
    border: 1px solid #829AFF;
    FONT-SIZE: 9px;
    background: #EAEEFF;
    HEIGHT: 20px;
    margin-top: 5px;
    margin-right: 70px;
   }
   #bgDiv {
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0px;
    left: 0px;
    right: 0px;
    background-color: #777;
    opacity: 0.7;
   }
        </style>
    </head>
 <body>
  <div id="bgDiv" style="display:none;">

</div>
     <a href="javascript:" onClick="bgDiv.style.display='';loginBox.style.display='';">登录</a>

<div id="loginBox" style="position:absolute; left:367px; top:150px; z-index:1;display: none;" >
            <div class="title" id="Mdown">
                <span class="t1">登录</span>
                <span class="t2" title="关闭" onClick="login.style.display='none';bgDiv.style.display='none'">X</span>
            </div>
            <div class="login">
                <form method="post" action="#">
                    <table>
                        <tr>
                            <td>用户名:</td><td><input type="text"name="username" size="12" maxlength="10"></td>
                        </tr>
                        <tr>
                            <td>密　码:</td><td><input type="text"name="password" size="12" maxlength="10"></td>
                        </tr>
                        <tr>
                            <td></td><td><button class="submit" type="submit">登陆</button></td>
                        </tr>
                    </table>
                </form>
            </div>
        </div>

<script type="text/javascript">
   var IsMousedown, LEFT, TOP, login;

document.getElementById("Mdown").onmousedown=function(e) {
    login = document.getElementById("loginBox");
    IsMousedown = true;
    e = e||event;
    LEFT = e.clientX - parseInt(login.style.left);
    TOP = e.clientY - parseInt(login.style.top);

document.onmousemove = function(e) {
     e = e||event;
     if (IsMousedown) {
      login.style.left = e.clientX - LEFT + "px";
      login.style.top = e.clientY - TOP + "px";
     }
    }

document.onmouseup=function(){
     IsMousedown=false;
    }
   }
        </SCRIPT>
</body>
</html>