How does Next js and ssr work?

Question

JavaScript

Wondering how ssr works. In particular next.js.
There are two options in mind:
1. The client makes the first request - he receives html filled with content with other resources.
Further, the application works like a regular SPA. The application becomes more SEO friendly and loads the first page faster.
2. Filled html is given for each client request. React plays the role of a templating engine. The application ceases to exist as a SPA.
How does it actually work?

Answer 1

First option.
The generated page with content is loaded. Scripts are loaded a little later. The page is alive. This process is called hydration.
The second option is you described Gatsby