//trim的定义
String.prototype.trim = function() { 
    var reExtraSpace = /^\s*(.*?)\s+$/; 
    return this.replace(reExtraSpace, "$1") 
};

 var str = "so  me" ;

 alert(str.trim()); //还是“so  me”  ?

function getHost(url) {
    var host = "null";
    if(typeof url == "undefined"|| null == url) {
        url = window.location.href;
    }
    var regex = /^\w+\:\/\/([^\/]*).*/;
    var match = url.match(regex);
   if(typeof match != "undefined" && null != match) {
        host = match[1];
    }
    return host;
};   

alert(getHost("www.sina.com"));  //null ?