<form name="myform" id="myform" action="ssss" method="post" onsubmit="getUrl();">

<script type="text/javascript">
   function getUrl(){  
    $('form').attr('action','new_url');       
   }
 </script>

function test1(){ 
  alert(document.myform.action);//返回值：http://localhost:8080/XXX/ssss
  alert(document.myform.attributes["action"].value);//返回值：ssss  与上一行有区别
//  以下三行，随便哪一行都行     
  document.getElementById('myform').action=‘new_url';
  document.myform.action=‘new_url';
  document.myform.attributes["action"].value = 'new_url';
}