javascript function will only works once
<p>I have a javascript function that is triggered onchange. What it does is take the value from a input field and then add it to the value entered in another field and then display the answer in a different field.</p>

<p>it works fine the first time, but when I enter a new value and leave the field there is an error: <code>TotalPurchasePrice is not a function</code></p>

<pre><code>function TotalPurchasePrice(BuyinPrice, TopupAmount) {
var BuyinPrice
var TopupAmount
BuyinPrice = BuyinPrice.toString().replace(/\£|\,/g, '');
TopupAmount = TopupAmount.toString().replace(/\£|\,/g, '');

TotalPurchasePrice = (BuyinPrice * 1) + (TopupAmount * 1);

document.getElementById('tTotalPurchasePrice').value = TotalPurchasePrice;
}
</code></pre>

<p>Can anyone tell me why this would only work once?</p>
