javascript验证，程序挺不下来，是怎么回事？
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <script language="javascript">
    function validate(){
        alert("error");
        document.form.username.focus();    
        return false;    
     }            
    </script>
  </head>
  <body>
    This is my JSP page. para<br>
  <form name="form">
            <input type="text" name="username">
            <input type="text" name="ip">
            <br>
            <input type="submit" name="submit" value="submit" onclick="validate();">
            <input type="reset" name="reset" value="reset">
        </form>
  </body>
</html>