实战题，鼠标拖拽效果教程-慕课网

index.html
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
 
<title>慕课网-拖拽效果</title>
 
<style type="text/css">
 
    body{ 
        background: url(images/baidu_demo.png) no-repeat top center #fff; 
        padding: 0px;margin: 0px;font-size: 12px;font-family: "微软雅黑";
    }
 
    .ui-dialog{
        width: 380px;height: auto;display: none;
        position: absolute;z-index: 9000;
        top: 100px;left: 100px;
        border: 1px solid #d5d5d5;background: #fff;
    }
    .ui-dialog a{ text-decoration: none;}
    .ui-dialog-title{
        height: 48px;line-height: 48px;padding-left: 20px;color: #535353;font-size: 16px;
        background: #f5f5f5;
        border-bottom: 1px solid #efefef;
        cursor: move;
    }
    .ui-dialog-title-closebutton{
        width: 16px;height: 16px;display: block;
        position: absolute;top: 12px;right: 20px;
        background: url(images/close_def.png);
    }
    .ui-dialog-title-closebutton:hover{
        background: url(images/close_hov.png);   
    }
    .ui-dialog-content{
        padding: 15px 20px;
    }
 
 
    .ui-dialog-pt15{
        padding-top: 15px;
    }
    .ui-dialog-l40{
        height: 40px;line-height: 40px;
        text-align: right;;
    }
 
    .ui-dialog-input{
        width: 100%;height: 40px;
        margin: 0px;padding: 0px;
        border: 1px solid #d5d5d5;
        font-size: 16px;color: #c1c1c1;
        text-indent: 25px;
        outline: none;
    }
    .ui-dialog-input-username{
        background: url(images/input_username.png) no-repeat;
    }
    .ui-dialog-input-password{
        background: url(images/input_password.png) no-repeat;
    }
 
    .ui-dialog-submit{
        width: 100%;height: 50px;display: block;
        font-size: 16px;color: #fff;
        background: #3b7ae3;
        text-align: center;line-height: 50px;
    }
    .ui-dialog-submit:hover{
        background: #3f81b0;
    }
 
    .ui-mask{
        width: 100%;height: 100%;background: #000;opacity: 0.4;filter: Alpha(opacity=40);
        position: absolute;top: 0px;left: 0px;z-index: 8000;display: none;
    }
 
    .link{
        text-align: right;line-height: 20px;padding-right: 40px;
    }
 
</style>
 
</head>
<body >
 
<div class="ui-dialog" id="dialog">
 
<div class="ui-dialog-title" id="dialogTitle">
            登录通行证
<a href="javascript:hideDialog();" class="ui-dialog-title-closebutton"></a>
</div>
<div class="ui-dialog-content">
 
 
<div class="ui-dialog-pt15 ui-dialog-l40">
<input type="text" value="手机/邮箱/用户名" class="ui-dialog-input ui-dialog-input-username">
</div>
<div class="ui-dialog-pt15 ui-dialog-l40">
<input type="text" value="密码" class="ui-dialog-input ui-dialog-input-password">
</div>
<div class=" ui-dialog-l40 ">
<a href="#">忘记密码</a>
</div>
<div>
 
<a href="#" class="ui-dialog-submit">登录</a>
 
</div>
<div class="ui-dialog-l40">
<a href="#">立即注册</a>
</div>
</div>
</div>
 
<div class="ui-mask" id="mask" onslectstart="return false"></div>
<div class="link">
<a href="javascript:showDialog();">登录</a>
</div>
 
 
<script type="text/javascript">
 
        //  获取元素对象
        function g(id){ return document.getElementById(id); }
 
        //  自动居中 - 登录浮层 ( el = Elemenet)
        function autoCenter( el ){
            var bodyW = document.documentElement.clientWidth;
            var bodyH = document.documentElement.clientHeight;
 
            var elW = el.offsetWidth;
            var elH = el.offsetHeight;
 
            el.style.left = ( bodyW - elW  ) / 2  + 'px';
            el.style.top  = ( bodyH - elH  ) / 2  + 'px';
        }
 
        //  自动全屏 - 遮罩
        function fillToBody( el ){
            el.style.width   =  document.documentElement.clientWidth  +'px';
            el.style.height  =  document.documentElement.clientHeight +'px';
        }
 
        var mouseOffsetX = 0;   //  偏移
        var mouseOffsetY = 0;
 
        var isDraging = false;  //  是否可拖拽的标记
 
        //  鼠标事件1 － 在标题栏上按下（要计算鼠标相对拖拽元素的左上角的坐标，并且标记元素为可拖动）
        g('dialogTitle').addEventListener('mousedown',function(e){
            var e = e || window.event;
            mouseOffsetX = e.pageX - g('dialog').offsetLeft;
            mouseOffsetY = e.pageY - g('dialog').offsetTop;
            isDraging = true;
        })
        //  鼠标事件2 － 鼠标移动时（要检测，元素是否可标记为移动，如果是，则更新元素的位置，到当前鼠标的位置［ps：要减去第一步中获得的偏移］）
        document.onmousemove = function( e ){
            var e = e || window.event;
 
            var mouseX = e.pageX;   // 鼠标当前的位置
            var mouseY = e.pageY;
 
            var moveX = 0;  //  浮层元素的新位置
            var moveY = 0;
 
            if( isDraging === true ){
 
                moveX = mouseX - mouseOffsetX;
                moveY = mouseY - mouseOffsetY;
 
                //  范围限定   moveX > 0 并且  moveX < (页面最大宽度 - 浮层的宽度)
                //            moveY > 0 并且  movey < (页面最大高度 - 浮层的高度)
 
                var pageWidth  = document.documentElement.clientWidth ;
                var pageHeight = document.documentElement.clientHeight ;
 
                var dialogWidth  = g('dialog').offsetWidth;
                var dialogHeight = g('dialog').offsetHeight;
 
                var maxX = pageWidth - dialogWidth;
                var maxY = pageHeight- dialogHeight;
 
                moveX = Math.min( maxX , Math.max(0,moveX) );
                moveY = Math.min( maxY , Math.max(0,moveY) );
 
                g('dialog').style.left = moveX + 'px';
                g('dialog').style.top  = moveY + 'px';
            }
 
        }
 
 
        //  鼠标事件3 － 鼠标松开的时候（标记元素为不可拖动即可）
        document.onmouseup = function(){
            isDraging = false; 
        }
 
     //  展现登录浮层
        function showDialog(){
【任务1】
            g('mask').style.display = 'block';
            autoCenter(g('dialog'));
            fillToBody( g('mask') );
        }
 
        //  隐藏登录浮层
        function hideDialog(){
            g('dialog').style.display = 'none';
            g('mask').style.display = 'none';
        }
 
【任务2】 =function(){
            autoCenter(g('dialog'));
            fillToBody( g('mask') ); 
        }
</script>
 
</body>
</html>