通过javascript扩展链接

function externallinks()
{
     if(!document.getElementsByTagName) return;
 
     var anchors = document.getElementsByTagName("a");
     for(var i=0; i<anchors.length; i++) {
          var anchor = anchors[i];
          if(anchor.getAttribute("href") && anchor.getAttribute("rel") == "external")
               anchor.target = "_blank";
     }
}
window.onload = externallinks;

文章来源：http://www.ifcode.net/?p=64