Unless has been designed to prevent FOUC and FOOC by inserting content while the DOM is still rendering.
As Unless uses a decoupled approach to guarantee easy implementation, FOUC is a valid concern. Through a smart script design, we prevent Flash Of Unstyled Content.
It works like this: the Unless script will load the personalized content in parallel with your web page. Then, while your web page is still loading like it normally would, we will replace original content with personalizations. So, we replace content before your web page even shows up in your visitors' browsers.
However, to achieve this, there are a few things that have to be taken into account:
If you have any questions or problems, contact us, so we can help you fix it.