<form method="post" action="/Tests/Post">
<fieldset>
<legend>What is Your Favorite Pet?</legend>
<input type="checkbox" name="favorite_pet" value="Cats" onclick="return ValidatePetSelection();">Java<br>
<input type="checkbox" name="favorite_pet" value="Dogs" onclick="return ValidatePetSelection();">Html<br>
<input type="checkbox" name="favorite_pet" value="Birds" onclick="return ValidatePetSelection();">Php<br>
<br>
<input type="submit" value="Submit now">
</fieldset>
</form>
<script type="text/javascript">
function ValidatePetSelection()
{
var checkboxes = document.getElementsByName("favorite_pet");
var numberOfCheckedItems = 0;
for(var i = 0; i < checkboxes.length; i++)
{
if(checkboxes[i].checked)
numberOfCheckedItems++;
}
if(numberOfCheckedItems > 2)
{
alert("You can't select more than two favorite pets!");
return false;
}
}
</script>