I'm trying to get the subtotal of the cart and subtract it from a value in javascript. This is my code:
<script type="text/javascript">
function minus_number() {
var a = document.querySelector("#spend");
var first_number = '50';
var second_number = '<?php echo $this->helper('checkout')->formatPrice(Mage::getSingleton('checkout/cart')->getQuote()->getGrandTotal()); ?>';
var result = parseInt(first_number) - parseInt(second_number);
a.innerHTML = result;
}
window.addEventListener("load",minus_number());
</script>
However it only shows NAN on the page. Any ideas what's wrong?