SOURCE

var str_url="ngoo";
document.write(IsURL(str_url));
function IsURL(str_url){ 
       var strRegex = "^((https|http|ftp|rtsp|mms)?://)"  
       + "?(([0-9a-z_!~*'().&=+$%-]+: )?[0-9a-z_!~*'().&=+$%-]+@)?" //ftp的user@  
       + "(([0-9]{1,3}\.){3}[0-9]{1,3}" // IP形式的URL- 199.194.52.184  
       + "|" // 允许IP和DOMAIN（域名） 
       + "([0-9a-z_!~*'()-]+\.)*" // 域名- www.  
       + "([0-9a-z][0-9a-z-]{0,61})?[0-9a-z]\." // 二级域名  
       + "[a-z]{2,6})" // first level domain- .com or .museum  
       + "(:[0-9]{1,4})?" // 端口- :80  
       + "((/?)|" // a slash isn't required if there is no file name  
       + "(/[0-9a-z_!~*'().;?:@&=+$,%#-]+)+/?)$";  
       var re=new RegExp(strRegex);  
 //re.test() 
       if (re.test(str_url)){ 
           return (true);  
       }else{  
           return (false);  
       } 
   }