Simpel addering med javascript

<script type="text/javascript">
function calc() {
    var val_1 = document.getElementById("one").value * 1,
    val_2 = document.getElementById("two").value * 1;
    alert(val_1 + val_2);
}
</script>

<input type="text" id="one">
<input type="text" id="two">
<input onclick="calc()" type="button" value="Udregn">