Hi,
You can change the code to this.
add_filter( 'woocommerce_loop_add_to_cart_link', 'add_to_cart_dofollow', 10, 2 );
function add_to_cart_dofollow($html, $product){
echo $product->add_to_cart_text();
if($product->add_to_cart_text()=="Add to cart") {
$html = sprintf( '<a rel="nofollow" href="%s" data-quantity="%s" data-product_id="%s" data-product_sku="%s" class="%s">%s</a>',
esc_url( $product->add_to_cart_url() ),
esc_attr( isset( $quantity ) ? $quantity : 1 ),
esc_attr( $product->get_id() ),
esc_attr( $product->get_sku() ),
esc_attr( isset( $class ) ? $class : 'button' ),
esc_html( $product->add_to_cart_text() )
);
}else {
$html = sprintf( '<a rel="dofollow" href="%s" data-quantity="%s" data-product_id="%s" data-product_sku="%s" class="%s">%s</a>',
esc_url( $product->add_to_cart_url() ),
esc_attr( isset( $quantity ) ? $quantity : 1 ),
esc_attr( $product->get_id() ),
esc_attr( $product->get_sku() ),
esc_attr( isset( $class ) ? $class : 'button' ),
esc_html( $product->add_to_cart_text() )
);
}
return $html;
}
Hope that helps.