How to check if an item is selected from an HTML drop down list?

<script>
var card = document.getElementById("cardtype");
if(card.selectedIndex == 0) {
     alert('select one answer');
}
else {
    var selectedText = card.options[card.selectedIndex].text;
    alert(selectedText);
}
</script>

Well you missed quotation mark around your string selectcard it should be "selectcard"

if (card.value == selectcard)

should be

if (card.value == "selectcard")

Here is complete code for that

function validate()
{
 var ddl = document.getElementById("cardtype");
 var selectedValue = ddl.options[ddl.selectedIndex].value;
    if (selectedValue == "selectcard")
   {
    alert("Please select a card type");
   }
}

JS Fiddle Demo