Sum of two textfields - javascript

Question

I found [this][1], rather difficult, javascript example online and I've implemented it with success in my website.

However, I would like to get the result of, in this case, the two subtotals in one new text-field.

The traditional getElementbyId and total.value=total didn't work out.

EDIT

 function doMath()
{
    // Capture the entered values of two input boxes
    var twogiga = document.getElementById('twogig').value;
    var fourgiga = document.getElementById('fourgig').value;

    // Add them together and display
    var sum = parseInt(twogiga) + parseInt(fourgiga);
    document.getElementById('total').value = parseInt(sum);
}

This is the javascript I use. But for some reason, when I have just one value (twogig), the total is set as NaN. What is wrong with my script?

Answer 1

Well, if you have assigned ID's to text inputs, for example: <input type="text" id="my_input" />, then you can call it with document.getElementById('my_input').value.

So:

<input type="text" id="my_input1" />
<input type="text" id="my_input2" />
<input type="button" value="Add Them Together" onclick="doMath();" />

<script type="text/javascript">
    function doMath()
    {
        // Capture the entered values of two input boxes
        var my_input1 = document.getElementById('my_input1').value;
        var my_input2 = document.getElementById('my_input2').value;

        // Add them together and display
        var sum = parseInt(my_input1) + parseInt(my_input2);
        document.write(sum);
    }
</script>

Naturally, that is a very basic script, it doesn't check to make sure the entered values are numbers. We have to convert the fields into integers, otherwise they'll be strings (so 2+2 would equal 22). When the button is clicked, the function is called, which makes a variable for each input box, converts them to ints, adds them, and outputs our sum.

Answer 2

Replace:

document.getElementById('total').value = parseInt(sum);

With:

document.getElementById('total').value = sum;

You have already done all the int-parsing you need to do.