title: How to use Javascript to set value of page element from APEX_ITEM
body: <p>I'm writing some code in Oracle Apex and I don't come from a development background, so pardon my bad code.  I'm dynamically generating a form and I want to set a hidden page item when the user changes the value of a specific form element.  Here is the code I'm using:</p>
  
  <pre><code>    select APEX_ITEM.HIDDEN(2,base_data_seq_nbr)||APEX_ITEM.HIDDEN(6,case when substr(description,0,1)= chr(49838) then substr(description,-(length(description)-1)) else description end)||APEX_ITEM.HIDDEN(7,case when substr(description,0,1)= chr(49838) then 1 else 0 end)||APEX_ITEM.HIDDEN(9,
                   data_select(replace(replace(trim(substr(field_name,-(length(field_name)-instr(field_name,',',1)))),'BSBR',''),'C','L'), substr(field_name,0,instr(field_name,',',1)-1), :P721_XCASE,:P721_XRETSTAT,:P721_XID,:P721_XCUSNUM,:P721_DB_ID))||case when substr(description,0,1)= chr(49838)
           then '&lt;img src="/i/themes/theme_2/images/required.gif" alt="Value Required" alt="Value Required" /&gt;'
           else null
         end as req_ind,
     case when substr(description,0,1)= chr(49838)
           then substr(description,-(length(description)-1))
           else description
         end as description,
     APEX_ITEM.DATE_POPUP(1,rownum,
                   to_date(data_select(replace(replace(trim(substr(field_name,-(length(field_name)-instr(field_name,',',1)))),'BSBR',''),'C','L'), substr(field_name,0,instr(field_name,',',1)-1), :P721_XCASE,:P721_XRETSTAT,:P721_XID,:P721_XCUSNUM,:P721_DB_ID),'MM/DD/YYYY'),'MM/DD/YYYY',10,10,'onkeyup="javascript:FormatDate(this);"' ||case when instr(substr(field_name,1,4),'DOB,',1)&gt;0 then ' onchange="javascript:$s(''P721_DOB_RBD'',this);"' end,'datepicker_'||rownum)
          end
     end as field_format
  from bcvsown.bcvs_base_data
      inner join v_lookup v
      on v.value_seq = stmt_type 
  left join (select * from apex_collections where collection_name = 'ERR_COLLECTION') ac
      on base_data_seq_nbr=ac.n001
  where caseno = :P721_XCASE
  and v.value_cd = case when :P721_XDE_SEQ &gt; 1 then decode(:P721_XIS_BSRS,'true','BSRS','BET') else v.value_cd end
  and db_id = :P721_DB_ID
  and v.type_cd = 'STMT_TYPE' 
  order by base_data_seq_nbr
  </code></pre>
  
  <p>The page renders as expected with no error and the page source shows the javascript settings   <code>(onchange="javascript:$s(''P721_DOB_RBD'',this);")</code> applied only to the elements I am aiming for.  But when I change the element, it doesn't seem to set the value of the hidden page item <code>(P721_DOB_RBD)</code>.</p>