How to increment a value after clicking a button on jsp?

Question

These are my JSP panels:

<dmf:panel name='panel43main'>
        <h2>
        <p style="text-indent:100px;text-align:justify">
              <dmf:dateinput name = 'BoiDate' tooltipnlsid='MSG_DATE'/> <dmf:button name='createpanel' cssclass="buttonLink" label='Add Date' onclick='onAddPanel' height='16' tooltipnlsid="MSG_OK_TIP"/>
        </p>
        </h2>
</dmf:panel>

Is there a way where when i click on the button(createpanel), ill increment a value inside the onAddPanel function? Thank you guys.