jQuery UI button and some calculations

Question

I have a list of checkboxes styled using JQuery UI as buttons. Each have a data-price attributem containing a price in this format: data-price="40.00", data-price="25.00" etc.

When the user "checks" a box, I am adding it's data-price to the totalPrice var. Every time another box is clicked, it's own data-price is added to the total. If the user unchecks a boxm, that value is taken away. I have tried to prevent the value from going under 0.00 as well.

I then output the totalPrice into a div - totalBox.

<script type="text/javascript">
 totalPrice = 0.00;
 $(function() {
 var totalBox = $('#totalBox');
 $( ".styled" ).button().bind('click', function() {
 var packagePrice = $(this).attr('data-price');
 var cost = parseFloat(packagePrice);
 if(totalPrice>=0.00) {
 if($(this).is(':checked')) {
 totalPrice += cost;
 } else {
 totalPrice -= cost;
 }
 }
 totalBox.html('<span class="total">Total:</span>
 <span class="price">&pound;' 
 + totalPrice.toFixed(2) + '</span>'
 );
 });
 });
</script>

I imagine there are some optimisations here - any thoughts?

Answer 1

When working with prices, then in my opinion it's usually a good idea to avoid floating point numbers. Binary rounding errors can easily strike unexpectedly any time.

Instead I'd suggest to work with integers (thus pennies) internally, and just add the decimal point for output.

An other unrelated point: I would move the hard-coded HTML in the script to the HTML document and only write the price.

• Calum: Good point about the integers, and I also agree with the HTML now that you mention it, thank you.

Answer 2

Few things:

1. The totalPrice variable should be declared inside your document.onready callback (and remember about var keyword). You should avoid global variables declaration.

2. You can prefix all variables which contain jquery object with $ sign to make code more readable.

<script type="text/javascript">
 $(function() {
 var totalPrice = 0.00;
 var $totalBox = $('#totalBox');
 $( ".styled" ).button().bind('click', function() {
 var packagePrice = $(this).attr('data-price');
 var cost = parseFloat(packagePrice);
 if(totalPrice>=0.00) {
 if($(this).is(':checked')) {
 totalPrice += cost;
 } else {
 totalPrice -= cost;
 }
 }
 $totalBox.html('<span class="total">Total:</span>
 <span class="price">&pound;' 
 + totalPrice.toFixed(2) + '</span>'
 );
 });
 });
</script>