[declarative-custom-elements] Use case: NO-JS

[sashafirsov]

Is it required that the solution run with without script turned off? Why?

Yes. Reasons:

• native browser performance. Which would make SSR obsolete for performance reasons.
• security. DCE have to be made without JS flaws of mixed context. And there is concept how to do so. 3rd party DCE should not be able to mess up the page or user input unless directed by page developer.
• low-powered in CPU and RAM devices would not need JS engine to interfere with infinite page life.

If there is doubt in any of statement, we can elaborate more.

[sashafirsov]

How DCE can improve web apps performance?

DCE parsing can be implemented by native browser HTML parser with streaming algorithm. Implementation of mozilla code for <custom-element> exist, other browser parsers is not a rocket science. The extending of HTML with DCE meant to be backward compatible.

The DCE declaration initialization can be done in parallel with parsing continuation. The declaration includes preparation of template, root and attributes defaults, loading dependencies, etc.

According to hydration rules, the insantiation of custom elements can be done in parallel as well. In case of "no side effect" principle honored on standardlevel, the custom elements instantiation also can be done in parallel with html parsing and DCE declarations.

As a disclimer, no such capabilities are possible with JS.