Add Back In Stock button to the product page for the Shopify Timber theme

button.html

<input type="submit" name="add" class="btn" id="addToCart" value="Add to Cart">
<input type="button" name="bis" class="btn-secondary" id="BIS_trigger" value="Email when available">

selectCallback.js

  if (variant.available) {
      // We have a valid product variant, so enable the submit button
      addToCart.removeClass('disabled').removeAttr('disabled').val('Add to Cart');

    } else {
      // Variant is sold out, disable the submit button
      addToCart.val('Sold Out').addClass('disabled').attr('disabled', 'disabled');
    }
    // rest of the function continues...