How can I tell if a checkbox is dynamicly checked?

Is there anyway in javascript to tell if a checkbox is checked, before the form is submited?

 

yes

<script type="text/javascript">
function checkForm() {
  if (document.getElementById('check1').checked==1) {
    // some code here
    return true;
  }
  else {
     // some code here
    return false;
  }
}
</script>
<form action="XX" method="XX" onSubmit="return checkForm();">
<input type="checkbox" id="check1" value="123" />
<input type="submit" value="Check" />
</form>

Code (markup):