opacity兼容写法

 .opacity{
     position: absolute;
     top: 0px;left: 0px;
     background: #000;
     filter:alpha(opacity=50);       /* IE */
     -moz-opacity:0.5;              /* 老版Mozilla */
     -khtml-opacity:0.5;              /* 老版Safari */
       opacity: 0.5;           /* 支持opacity的浏览器*/
 }

Js写法

 object.filter = "alpha(opacity=" + opacity + ")";  /* IE */
 object.MozOpacity = (opacity / 100);           /* 老版Mozilla */
 object.KhtmlOpacity = (opacity / 100);           /* 老版Safari */
 object.opacity = (opacity / 100);           /* 支持opacity的浏览器*/