Question

I am using this code for my form

Total: <input name="total" id="total" type="text" readonly="readonly" style="background-color:#eee;" value="<? echo $total; ?>" /><br /><br />
Cash: <input name="cash" id="cash" type="text" /><br /><br />
Change: <input name="change" id="change" type="text" readonly="readonly" style="background-color:#FF0;"/>

The total comes from php e.g 25.00, i want to be able to put a number e.g 30.00 in cash and then the change says e.g. 5.00 and i want it to change on key up so if i change the amount it re-calculates,

Can anyone help with the JavaScript to make the calculation work,thanks

Answer 1

Add an onchange and onkeyup event handler for the ‘cash’ element. Then make the calculations in the handler.

Example:

Cash: <input name="cash" id="cash" type="text" onkeyup="Recalculate();" onchange="Recalculate()" /><br /><br />

In Javascript:

function Recalculate()
{
var total = parseInt(document.getElementById("total").value, 10);
var cash = parseInt(document.getElementById("cash").value, 10);

document.getElementById("change").value = (total-cash);
}