原生js实现可拖动的登录框效果
实现原理
1.onmousemove事件触发时不断更新鼠标的pageXY改变位置，
登陆框的偏移量=鼠标当前位置-鼠标到登录框边框的距离
2.onmousedown鼠标摁下时触发事件获取鼠标到登陆框的距离，再设置true允许拖拽
3.onmouseup鼠标弹起设置false停止拖拽
4.登录框居中显示公式：(可视区域宽高-登录框宽高)/2
5.当浏览器窗口大小变化时触发事件window.onresize再更新登陆框居中显示
代码中有详细的注释
完整代码
<!DOCTYPEhtmlPUBLIC"-//W3C//DTDXHTML1.0Transitional//EN""http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<htmlxmlns="http://www.w3.org/1999/xhtml">
<head>
<metahttp-equiv="Content-Type"content="text/html;charset=utf-8"/>
<title>demo</title>
<style>
body,h1,h2,h3,h4,h5,h6,hr,p,blockquote,dl,dt,dd,ul,ol,li,pre,form,fieldset,legend,button,input,textarea,th,td{margin:0;padding:0;}
body,button,input,select,textarea{font:12px/1.5tahoma,arial,\5b8b\4f53;}
h1,h2,h3,h4,h5,h6{font-size:100%;}
address,cite,dfn,em,var{font-style:normal;}
code,kbd,pre,samp{font-family:couriernew,courier,monospace;}
small{font-size:12px;}
ul,ol{list-style:none;}
a{text-decoration:none;}
a:hover{text-decoration:underline;}
sup{vertical-align:text-top;}
sub{vertical-align:text-bottom;}
legend{color:#000;}
fieldset,img{border:0;}
button,input,select,textarea{font-size:100%;}
table{border-collapse:collapse;border-spacing:0;}
.clear{clear:both;float:none;height:0;overflow:hidden;}
/*p{font-size:100px;}*/
#btn{width:80px;
height:40px;
background:#3b7ae3;
margin:0auto;
display:block;
cursor:pointer;
border-style:none;
color:#fff;
font-size:16px;}
#mask{
background:#000;
opacity:0.75;
filter:alpha(opacity=75);
height:1000px;
width:100%;
position:absolute;
left:0;
top:0;
z-index:1000;
}
#login{position:absolute;top:100px;left:100px;width:400px;height:auto;border:1pxsolid#d5d5d5;z-index:1001;}
.title{position:relative;background-color:#f7f7f7;cursor:move;height:50px;line-height:50px;font-size:16px;color:#333;padding-left:30px;}
.close{position:absolute;top:0;right:10px;color:#ccc;}
.content{background:#fff;padding:15px20px;}
.user{margin-bottom:15px;}
.password{margin-bottom:15px;}
.pt{display:block;
height:38px;
padding-left:15px;
border:1pxsolid#ddd;
transition:.3s;
font-size:14px;
color:#666;
width:343px;
}
.sm{display:block;
height:48px;
border:1pxsolid#ddd;
transition:.3s;
font-size:16px;
color:#666;
width:360px;
background:#3b7ae3;
color:#fff;}
</style>
</head>
<body>
<!--<divid="mask"></div>-->
<buttonid="btn"href="">登录</button>
<!--<divclass="login"id="login">
<divclass="title"id="title">登录百度账号<ahref="#"class="close">x</a></div>
<divclass="content">
<divclass="user"><inputclass="pt"type="input"value="手机/邮箱/用户名"></div>
<divclass="password"><inputclass="pt"type="input"value="密码"></div>
<divclass="submit"><inputclass="sm"type="submit"value="登录"></div>
</div>
</div>-->
<scripttype="text/javascript">
functionb(){
//创建遮罩层div并插入body
varmask=document.createElement("div");
mask.id="mask";
mask.style.height=cheight+"px";
//宽度直接用100%在样式里
document.body.appendChild(mask);
//创建登录层div并插入body
varlogin=document.createElement("div");
login.id="login";
login.innerHTML='<divclass="title"id="title">登录百度账号'+'<ahref="#"class="close">x</a>'+'</div>'+
'<divclass="content">'+'<divclass="user">'+'<inputclass="pt"type="input"value="手机/邮箱/用户名">'+'</div>'+'<divclass="password">'+'<inputclass="pt"type="input"value="密码">'+'</div>'+'<divclass="submit">'+'<inputclass="sm"type="submit"value="登录">'+'</div>'+'</div>';
document.body.appendChild(login);
//窗口可视区域宽度
varcwidth=document.documentElement.clientWidth||document.body.clientWidth;
//窗口可视区域高度
varcheight=document.documentElement.clientHeight||document.body.clientHeight;
//登录框宽度
varlwidth=login.offsetWidth;
//登录框高度
varlheight=login.offsetHeight;
//设置登录框的居中显示
login.style.left=(cwidth-lwidth)/2+"px";
login.style.top=(cheight-lheight)/2+"px";
//设置遮罩层的高度
mask.style.height=cheight+"px";
//改变窗口大小后依然居中显示
window.onresize=function(){
if(document.compatMode=="CSS1Compat"){
cwidth=document.documentElement.clientWidth;
cheight=document.documentElement.clientHeight;
}else{
cwidth=document.body.clientWidth;
cheight=document.body.clientHeight;
}
login.style.left=(cwidth-lwidth)/2+"px";
login.style.top=(cheight-lheight)/2+"px";
mask.style.height=cheight+"px";
}
//获取拖拽容器
vartitle=document.getElementById("title");
varisDraging=false;
varmouseOffsetX;
varmouseOffsetY;
//鼠标按下事件
title.onmousedown=function(e){
vare=e||window.event;
/*varel=e.srcElement;
if(!el){
el=e.target;//兼容火狐
}*/
//鼠标相对于登录框的位置
mouseOffsetX=e.pageX-login.offsetLeft;
mouseOffsetY=e.pageY-login.offsetTop;
//鼠标摁下时为true
isDraging=true;
/*console.log(mouseOffsetY,mouseOffsetX)*/
}
//鼠标移动事件
document.onmousemove=function(e){
vare=e||window.event;
//鼠标移动时的坐标
varnewMX=e.pageX;
varnewMY=e.pageY;
//判断为true时可以拖拽
if(isDraging===true){
//登录框的偏移值=当前位置-鼠标到登录框的距离
varloginL=newMX-mouseOffsetX;
varloginT=newMY-mouseOffsetY;
//如果lefttop值超过边缘时就让他等于边缘
if(loginL<0){
loginL=0;
}elseif(loginL>(cwidth-lwidth)){
loginL=cwidth-lwidth;
}
if(loginT<0){
loginT=0;
}elseif(loginT>(cheight-lheight)){
loginT=cheight-lheight;
}
login.style.left=loginL+"px";
login.style.top=loginT+"px";
}
}
//鼠标弹起时设置为不可拖拽
document.onmouseup=function(){
isDraging=false;
}
//点击X关闭登录框和弹出层
varclose=login.getElementsByClassName("close")[0];
close.onclick=function(){
document.body.removeChild(mask);
document.body.removeChild(login);
}
}
//点击登录弹出登录框和弹出层
window.onload=function(){
varbtn=document.getElementById("btn");
btn.onclick=function(){
b();
}
}
</script>
</body>
</html>
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