Aantal check

<script>
function check(obj)
{
  tel = 0;
  y = obj.options.length;
  for(x=0;x<y;x++)
  {
    if(obj.options[x].selected)
    {
      tel++;
    }
  }
  if(tel > 2)
  {
    alert("Je hebt te veel Options geselecteerd.");  
  }
}
</script>
<select multiple="multiple" onchange='check(this)'>
...
</select>

<script>
function check(obj)
{
  tel = 0;
  y = obj.options.length;
  for(x=0;x<y;x++)
  {
    if(obj.options[x].selected)
    {
      tel++;
    }
  }
  if(tel > 2)
  {
    alert("Je hebt te veel Options geselecteerd.");  
  }
}
</script>
<select multiple="multiple" onchange='check(this)'>
...
</select>

<script>
function count_checkbox()
{
  var obj = document.getElementsByTagName("input");
  var y = obj.length;
  var tel = 0; 
  for(var x=0;x<y;x++)
  {
    if(obj[x].type == "checkbox" && obj[x].checked)
    {
      tel++;
    }
  }
  if(tel > 2)
  {
    alert("Je hebt te veel Checkboxen aangevinkt.");  
  }
}
</script>
<input type='checkbox' onclick='count_checkbox()'>
<input type='checkbox' onclick='count_checkbox()'>
<input type='checkbox' onclick='count_checkbox()'>

<script>
function count_checkbox()
{
  var obj = document.getElementsByTagName("input");
  var y = obj.length;
  var tel = 0; 
  for(var x=0;x<y;x++)
  {
    if(obj[x].type == "checkbox" && obj[x].checked)
    {
      tel++;
    }
  }
  if(tel > 2)
  {
    alert("Je hebt te veel Checkboxen aangevinkt.");  
  }
}
</script>
<input type='checkbox' onclick='count_checkbox()'>
<input type='checkbox' onclick='count_checkbox()'>
<input type='checkbox' onclick='count_checkbox()'>