var pathName=window.document.location.pathname;
    var curWwwPath=window.document.location.href;
    var pos=curWwwPath.indexOf(pathName);
    var prefixUrl=curWwwPath.substring(0,pos);
    console.log("pathName:"+pathName);
    console.log("curWwwPath:"+curWwwPath);
    console.log("pos:"+pos);
    console.log("prefixUrl:"+prefixUrl);

我丢服务器上，看下结果：

然后你就知道了吧，取你所需呗~