函数计算折扣两次

Question

For the life of me I can't seem to figure out why this function won't calculate correctly. If I run this function the discount ( totalPrice ) is applied twice, for example: 20*1.05 == 21 , but when the function runs and it gives me 22.05 .

What am I doing wrong? Thanks for the help.

<script type="text/javascript">
    function codeDiscount() {
        var totalCost = document.getElementById('total').value;
        var custCode = document.getElementById('coupon').value; 

        if (custCode == "ABCD" || custCode == "EFGH")
        {
            totalCost = document.getElementById('total').value; 
            var totalPrice = parseInt(totalCost) * 1.05;
            document.getElementById('total').value = totalPrice;
        }
    }
</script>

Answer 1

I suspect that the problem isn't in this code block. Is there anything that would cause codeDiscount() to be called a second time?

Answer 2

I suspect there is something wrong with ur code:

 <script type="text/javascript">
    function codeDiscount() {
        var totalCost = document.getElementById('total').value;
        var custCode = document.getElementById('coupon').value; 

        if (custCode == "ABCD" || custCode == "EFGH")
        {
            var totalPrice = parseInt(totalCost) * 1.05;
            document.getElementById('total').value = totalPrice;
        }
    }
</script>

Also, please make sure that you don't call the same function twice. Otherwise, the result will be incorrect.

Answer 3

If your total field is being updated every time something changes, it's better to adopt this:

Store the total value in a separate variable:

var cartTotal = 0;

Then, whenever the sum of items changes, you update it:

// calculate sum of all products
cartTotal = 0;
for (var i in all_products) {
    cartTotal += all_procucts[i].price;
}
// calculate discount
codeDiscount();

To recalculate discount you use the cartTotal but you only update the field

var totalPrice = cartTotal;

if (custCode == 'ABCD') {
    totalPrice *= 1.05;
}

document.getElementById('total').value = totalPrice;