I get the following error and I can't find why:

> 
> TypeError: object is not a function
> 
> 
> 

Here is my html:

```
<td><input type="text" value="" id="cash_retained" name="cash_retained" onkeyup="net_cash()" size="25"></td>
<td><input type="text" value="" id="cash_change" name="cash_change" onkeyup="net_cash()" size="25"></td>
<td><input type="text" value="0" id="net_cash" name="net_cash"></td>

```

Here is my js function:

```
function net_cash() {
    var cash = 0;
    var retained = document.getElementById("cash_retained");
    var change = document.getElementById("cash_change");

    cash += parseInt(retained.value);
    cash += parseInt(change.value);

    if (isNaN(cash)) {
        document.getElementById("net_cash").value = "0";
    } else {
        document.getElementById("net_cash").value = cash;
    }
}

```

I can't see for the life of me why this is not working. I have other similar js functions that are finding it just fine.