JavaScript webpage

I am having trouble debugging my JavaScript webpage. Where I am having difficulty is where I marked (...). I get errors of undefined. Do I place my parameters from my function countDown(start, increment) which are start and increment into (...)?

<dl>
startNum:&nbsp;&nbsp;<input type="text" id="<!-- (...) -->"/>
countBy:&nbsp;&nbsp;<input type="text" id="<!-- (...) -->"/>
<br/>
<input type="button" value="Run Function" onClick="onClickFunc5()" />
<script>
   function onClickFunc5()
   {
      var startNum = document.getElementById('<!-- (...) -->').value;
      var countBy = document.getElementById('<!-- (...) -->').value;

      <!-- countDown(start, increment) -->
      <!-- (...) -->
   }
</script>

I would try this:

startNum:&nbsp;&nbsp;<input type="text" id="startInput"/>
countBy:&nbsp;&nbsp;<input type="text" id="countByInput"/>
<br/>
<input type="button" value="Run Function" onClick="onClickFunc5()" />
<script>
   function onClickFunc5()
   {
      var startNum = document.getElementById('startInput').value;
      var countBy = document.getElementById('countByInput').value;

      <!-- countDown(startNum, countBy) -->
      <!-- (...) -->
   }
</script>

Did you create the countDown function yourself or is it part of a plugin that you want to use? You may not be including the plugin that you need.

Also, you never closed the dl tag