As a unified approach to the design of SPA (search engines and browsers), add information about your mini-framework includeHTML
which allows just:
1. To generate a template that can start and run entirely locally (no server!), dynamically loading the desired page block.
2. It's very easy to create a SPA containing different information blocks that can be separated to give from the server, and for PS(search engines) - stitch in a single HTML page on the server side.
3. Quickly understand how to use.
In terms of fast template engine for JSON on the client side - I can advise REX Tiny Templater