How to build a SPA from a multi-page site without losing search traffic?

Question

Angular

Both Angular.JS and React.JS build their house entirely in JavaScript. And it turns out that search robots get empty pages with a bunch of javascript.
Assuming that we already have a ready-made site consisting of a backend and a regular layout. How to make SPA out of it? Yes, so that the template is completely preserved for the bot, and for a regular user (having JS enabled) everything happens like in SPA. Only native JavaScript? Popular frameworks do not know how to do this?

Answer 1

The answer is simple - server rendering of pages. All modern frameworks can do this:
- https://angular.io/guide/universal
- https://css-tricks.com/server-side-react-rendering/
- https://vuejs.org/v2/guide/ ssr.html

Answer 2

If you can return content by nodes from the backend, you can do this:
1. Create an API on the backend when specific nodes (GUI blocks) return
2. On the front - use includeHTML when you need to make transitions and load different content in different blocks.
This will speed up the site for the end user without losing current positions in search engines and with minimal code rewriting.