JavaScript获取网站根目录地址

function getRootPath(){ 
    var strFullPath=window.document.location.href; 
    var strPath=window.document.location.pathname; 
    var pos=strFullPath.indexOf(strPath); 
    var prePath=strFullPath.substring(0,pos); 
    var postPath=strPath.substring(0,strPath.substr(1).indexOf('/')+1); 
    return(prePath+postPath); 
}
var webpath=getRootPath();  //webpath就是目录路径变量