gistfile1.js

// Example code only
// This hasn't been tested on a real site. Please backup your theme before making any changes.

var selectCallback = function(variant, selector) {
    if (variant && variant.available) {
      jQuery('#add-to-cart').removeAttr('disabled').removeClass('disabled'); // remove unavailable class from add-to-cart button, and re-enable button
      if(variant.price < variant.compare_at_price){
        jQuery('#price-preview').html(Shopify.formatMoney(variant.price, "${{amount}}") + " <del>" + Shopify.formatMoney(variant.compare_at_price, "${{amount}}") + "</del>");
      } else {
        jQuery('#price-preview').html(Shopify.formatMoney(variant.price, "${{amount}}"));
      }
    } else {
      jQuery('#add-to-cart').addClass('disabled').attr('disabled', 'disabled'); // set add-to-cart button to unavailable class and disable button
      var message = variant ? '<input type="button" id="BIS_trigger" class="btn" value="Email me when in stock">' : "Unavailable";
      jQuery('#price-preview').html(message);
    }
  };