I am learning the concepts and coding pattern of server-side-rendering of js frameworks - reactjs - and I read articles that it is used for better seo , loading content befor javascript coming into play, better UI and so on. I have seen many website including hashnode and the react.org and many that these website are having some pre-loading style of the component like a sliding lights inside the component which is awsome pre-loading style and I liked it a lot . And I was wondering whether it is done using SSR or not.