为什么javascript不起作用呢!?
我用的是struts框架,有一个注册表单,为什么我写的javascript验证这个表单不起作用呢?下面是代码! 
  <%@   page   language= "java "   pageEncoding= "gb2312 "   %>  
  <%@   taglib   uri= "http://jakarta.apache.org/struts/tags-bean "   prefix= "bean "%>     
  <%@   taglib   uri= "http://jakarta.apache.org/struts/tags-html "   prefix= "html "%>  
  <html>     
  <head>  
  <script   language= "javascript ">  
 function   checkform(form){ 
 if   (form.userName){ 
 if   (form.userName.value== " ") 
 { 
 alert   ( "请输入用户名 "); 
 form.userName.focus(); 
 return   (false); 
 } 
 } 
 if(form.password){ 
 if(form.password.value== " ") 
 { 
 alert   ( "输入密码 "); 
 form.password.focus(); 
 return   (false); 
 } 
 } 
 if(form.psw){ 
 if(form.psw.value!=form.password.value) 
 { 
 alert   ( "两次密码不一样 "); 
 form.psw.focus(); 
 return   (false); 
 } 
 } 
 if   (form.email){ 
 if   (form.email.value   ==    " "||form.email.value.indexOf( "@ ")==-1){ 
 alert( "请输入合适的E-MAIL地址! "); 
 form.email.focus(); 
 return   (false); 
 } 
 } 
  </script>  
 	 </head>  
 	 <body>  
 		 <html:form   action= "/register "   method= "post "   >  
 		 <table   width= "43% "   border=1   align= "center "   cellpadding= "0 "   cellspacing= "0 ">  
 		 <tr>  
 		 <td> 用户名: </td>  
 		 <td>  <html:text   property= "userName "   size= "20 "/>  <br>  </td>  
 		 </tr>  
 		 <tr>  
 		 <td> 密码: <br>  </td>  
 		 <td>  <html:password   property= "password "   size= "20 "/>  <br>  </td>  
 		 </tr>  
 		 <tr>  
 		 <td> 确认密码: <br>  </td>  
 		 <td>  <html:password   property= "psw "/>  <br>  </td>  
 		 </tr>  
 		 <tr>  
 		 <td> 年龄: <br>  </td>  
 		 <td>  <html:text   property= "age "/>  <br>  </td>  
 		 </tr>  
 		 <tr>  
 		 <td> 性别: <br>  </td>  
 		 <td>  <html:radio   property= "sex "   value= "male "/> 男 
 		 <html:radio   property= "sex "   value= "female "/> 女 </td>  
 		 </tr>  
 		 <tr>  
 		 <td> 职业: <br>  </td>  
 		 <td>  <html:select   property= "carrer ">  <html:option   value= "老师 "> 老师 </html:option>  
 		 <html:option   value= "记者 "> 记者 </html:option>  
 		 <html:option   value= "学生 "> 学生 </html:option>  
 		 <html:option   value= "商人 "> 商人 </html:option>  
 		 <html:option   value= "农民 "> 农民 </html:option>  
 		 <html:option   value= "工人 "> 工人 </html:option>  
 		 <html:option   value= "医生 "> 医生 </html:option>  
 		 <html:option   value= "其他 "> 其他 </html:option>  
 		 </html:select>  <br>  </td>  
                          </