Addition of Two Numbers using javascript

n1 <input type = "number" id = "n1" value=15 />
n2 <input type = "number" id = "n2" value=20 />

<p>Sum?</p>
<button onclick="sum()">Try it</button>
<p id="demo2">Result?? </p>

<script type="text/javascript">

 function sum()
{
    var fn, ln;

    fn = document.getElementById("n1").value;

    ln = document.getElementById("n2").value;

    result =  (parseFloat(fn)+parseFloat(ln));

    document.getElementById("demo2").innerHTML = result;

}

</script>