function getDomain(url)
{  
   if(url.indexOf('//')>-1){
    var st = url.indexOf("//",1);
    var _domain = url.substring(st+1, url.length) ;
    var et = _domain.indexOf("/",1);
    _domain = _domain.substring(1,et) ;
    strs=_domain.split(".");    
    return strs[strs.length-2]+"."+strs[strs.length-1];
    }
     return url;
   }

alert( getdomain("http://www.zshare.net/1/2.htm") )
//结果是：zshare.net