Unable to multiply without pressing button

Dear friends,
I have two textboxes

<input type="text" name="price" size="20">
<input type="text" name="quantity" size="20">

In the price textbox the price is already entered. I want to automatically calculate total price by multiplying
price * quantity without pressing of calculate button (if one entered 1 in quantity it will automatically get
multiplied with price and get entered into third box, if it adds 0 with 1 i.e. 10 it target box autmatically updated).
It should also checkthe quantity only contain number.
I have trried a lot but failed. Please give any hint idea or code.
Thanks

what about calling the function onChange()

You could right a function that is called onchange or onkeyup in the quantity box.

It can do the checking for you

Code: Select all

<script type="text/javascript">

function updateAndCheck(quant, price, total)

{
    price = document.getElementById(price);
    total = document.getElementById(total);

    if (!isNaN(parseInt(quant.value)))
       total.value = (parseInt(price.value) * parseInt(quant.value));
    else {
       alert ("Numbers only please!")
       quant.value= '';
    }
}

</script>
<input type="text" name="price" size="20" id="price" />
<input type="text" name="quantity" value="" onkeyup="updateAndCheck(this, 'price', 'total')" id="quantity" size="20" />
<input type="text" name="total" value="" id="total" />

That will perform the necessary calculations and checks when the user has typed something in the box. No need to push a button at all.

Cheers,