Javascript returning NaN

I'm attempting to display a subtotal each time a customer enters a quantity. However, when I loop through my inputs, I get a NaN as the开发者_如何学Python total. I believe it may be the way I'm declaring the subtotal variable in my script, but I haven't come across this before:

$('.item-qty input').bind('keyup', function(){

   var subtotal = 0.0;

   $('.item-qty input').each(function(){
      var class = $(this).attr('id');
      var qty = $(this).val();                     
      var price = $('.'+class).html();

      price = parseFloat(price);
      qty = parseInt(qty);
      subtotal = subtotal + (price * qty);
   });

   $('.subtotal input').val(subtotal);
});

parseFloat and parseInt can return NaN if the first character of the string cannot be converted to a number.

So, I would safeguard against it like this (NaN is a falsy value):

price = parseFloat(price) || 0;
qty = parseInt(qty, 10) || 0;

Arithmetic operations on numbers with the value NaN almost always result in NaN (NaN + 5 will result in NaN.) That means, if only one of the input cannot be parsed by parseFloat or parseInt, your current code would end up calculating NaN for the subtotal.

It's already been mentioned in the comments (by Felix mostly) but I think it's worth the emphasis as these are important concerns:

• Always pass the radix argument to the parseInt function;
• Do not use class for variable names: It's a reserved (not used, but reserved) keyword;
• Don't expect the subtotal to be perfectly accurate unless you do your calculations in cents.