Error JavaScript in JSF Portlet When use Richfaces!

[phanthang1988]

Hello Everybody!
I'm a student come from VietNam!
I'm studying about Richface framework!
I had got a problem in JSF(Richface) Portlet when I used JavaScript!
That problem is : I could not get a value into a <h:inputText />  with JavaScript!
Can anybody help me?
Thank you very much!

This is my code:

<ui:composition xmlns="http://www.w3.org/1999/xhtml"
     xmlns:f="http://java.sun.com/jsf/core"
     xmlns:ui="http://java.sun.com/jsf/facelets"
     xmlns:h="http://java.sun.com/jsf/html">

    <f:view>
         <script type="text/javascript">
         function check() {
              var result = document.getElementById("myform:form").value;
                      alert(result);
         }
          </script>

        <h:form id="myform">

                   <h3>Hello :</h3>

                    <h:inputText value="" id="form" />

                    <h:commandButton value="OK"  onclick="check();"/>

                                 </h:form>

        </f:view>

</ui:composition>

And this is a error report in a Error Console in Firefox:

Can anybody help me?

Thank you very much!

ThangPhan!