1.遮罩层的宽度和高度是js获取页面的宽高（页面内容）
//获取遮罩层(内容)的高度和宽度 var sHeight=document.documentElement.scrollHeight; var sWidth=document.documentElement.scrollWidth;
2.登录框设置静止定位fixed
3.登录框居中显示公式：(可视区域宽高-登录框宽高)/2
//获取login的宽度和高度并设置偏移值 var dHeight=oLogin.offsetHeight; var dWidth=oLogin.offsetWidth; oLogin.style.left=(sWidth-dWidth)/2+"px"; oLogin.style.top=(wHeight-dHeight)/2+"px";
完整代码
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-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/1.5 tahoma,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:courier new,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;} #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: fixed; left: 30%; top: 30%; z-index:1001; } .loginCon{ width: 670px; height: 380px; background: #fff; border:5px solid #F01400; } #close{ width: 30px; height: 30px; background: blue; cursor: pointer; position: absolute; right: 10px; top: 10px; } #btnLogin{ width: 80px; height: 40px; background: #F01400; margin:0 auto; display: block; cursor: pointer; border-style: none; color: #fff; font-size: 16px; } </style> </head> <body> <button>登录</button> <!-- <div></div> <div> <div> <div></div> </div> </div> --> <p>1</p> <p>1</p> <p>1</p> <p>1</p> <p>1</p> <p>1</p> <p>1</p> <p>1</p> <p>1</p> <p>1</p> <script type="text/javascript"> function openNew(){ //获取页面body！内容！的高度和宽度 var sHeight=document.documentElement.scrollHeight; var sWidth=document.documentElement.scrollWidth; //获取可视区域高度，宽度与页面内容的宽度一样 var wHeight=document.documentElement.clientHeight; //创建遮罩层div并插入body var oMask=document.createElement("div"); oMask.id="mask"; oMask.style.height=sHeight+"px"; //宽度直接用100%在样式里 document.body.appendChild(oMask); //创建登录层div并插入body var oLogin=document.createElement("div"); oLogin.id="login"; oLogin.innerHTML="<div><div></div></div>" document.body.appendChild(oLogin); //获取login的宽度和高度并设置偏移值 var dHeight=oLogin.offsetHeight; var dWidth=oLogin.offsetWidth; oLogin.style.left=(sWidth-dWidth)/2+"px"; oLogin.style.top=(wHeight-dHeight)/2+"px"; //获取关闭按钮 var oClose=document.getElementById("close"); oMask.onclick=oClose.onclick=function(){ document.body.removeChild(oMask); document.body.removeChild(oLogin); } } window.onload=function(){ var oBtn=document.getElementById("btnLogin"); oBtn.onclick=function(){ openNew(); } } </script> </body> </html>