Binding: Javascript?

[Blue Chrome]

I have an input form set up for financials, and I would like for the subtotals boxes at the bottom to add together whatever the user enters into the text boxes (dynamically). I am using standard text boxes (input instead of cfinput), and I have not set up the form yet (using spry tabs, and when I try to have them all on the same form, they "un-tab" - different subject).
At first I thought I could just bind the subtotal text boxes to the input boxes:
<input id="SubTotal_1" type="text" bind="{Fund1_1}+{Fund1_2}+{Fund1_3}/>
but when I enter numbers in the input boxes, nothing shows up in the subtotal box. Then I though maybe a function would work so I set up a JavaScript function:
<script type="text/javascript">
Function doAdd(a,b,c)
{SumX=a+b+c;
return SumX;}
</script>
When I call the doAdd() function in a button or something, it works, but I want it to be dynamic. Any ideas?

[Blue Chrome]

I got it. I was having problems passing the field id's as variables, but I FINALLY got it to work. The function is like this:
<script type="text/javascript">
function doAdd(a,b,c,d,e,X)
{
var numVal1=parseInt(document.getElementById(a).value);
var numVal2=parseInt(document.getElementById(b).value);
var numVal3=parseInt(document.getElementById(c).value);
var numVal4=parseInt(document.getElementById(d).value);
var numVal5=parseInt(document.getElementById(e).value);
var totalValue = numVal1+numVal2+numVal3+numVal4+numVal5;
document.getElementById(X).value=totalValue;
}
</script>

And in each text box (except the subtotal box) I have to code this:

onchange="doAdd('Fund1_1','Fund1_2','Fund1_3','Fund1_4','Fund1_5','SubTotal_1b')"

But this works great, now I can use the same function for all of the subtotals on my form. Whoopee!