Add Variant ID Url switching

theme.js.liquid

 $container.on(theme.Variants.eventStrs.onVariantChanged, function (e, variant) {
          if (variant) {
            if(window.location.pathname.indexOf('product') >= 0){
              var newurl = window.location.protocol + '//' + window.location.host + window.location.pathname + '?variant=' + variant.id;
              window.history.replaceState({path: newurl}, '', newurl);
            }
            self._changeImage($container, variant);
            self._changePrice($container, variant);
            self._changeSKU($container, variant);
            self._updateAvailability($container, variant.available);
            $('.shopify-payment-button').show();    
            self._changeMetafield($container, variant);
          } else {
            if(window.location.pathname.indexOf('product') >= 0){
              var newurl = window.location.protocol + '//' + window.location.host + window.location.pathname;
              window.history.replaceState({path: newurl}, '', newurl);
            }
            $('.shopify-payment-button').hide();
            self._changePrice($container, null);
            self._changeSKU($container, null);
            self._updateAvailability($container, false, '{{ 'products.product.unavailable' | t }}');
                                     }
                                     });
            //Set up the listener for when a new quantity is entered
            $container.on(theme.Variants.eventStrs.onQtyChanged, function (e, newQuantity) {
              var $selection = theme.Variants.getSelectedVariant($container);
              self._updatePrice($container, $selection.data('base-price'), $selection.data('compare-price'), newQuantity);
            });
          },