magento update cart and checkout

magento_update_cart_and_checkout.php

<?php if ($this->isPossibleOnepageCheckout()):?>
    <script type="text/javascript">
    // <![CDATA[
      function updateAndGoto(url) {
          var cartForm = $$('.cart form').first();
          var action = cartForm.readAttribute('action');
          if (action.indexOf('return_url') < 0) {
              var glue = action.indexOf('?') < 0 ? '?' : '&';
              action += glue + 'return_url=' + url;
              cartForm.writeAttribute('action', action);
          }

          cartForm.submit();
      }
    // ]]>
    </script>
    <button type="button" title="<?php echo $this->__('Proceed to Checkout') ?>" class="button btn-proceed-checkout btn-checkout<?php if ($this->isDisabled()):?> no-checkout<?php endif; ?>"<?php if ($this->isDisabled()):?> disabled="disabled"<?php endif; ?> onclick="updateAndGoto('<?php echo $this->getCheckoutUrl() ?>');"><span><span><?php echo $this->__('Proceed to Checkout') ?></span></span></button>
<?php endif?>