[kaoD]

Not sure I agree with the example at all. Maybe I didn't understand?

> you'd have logic that sends JSON and checks that, and on the server side you'd need logic that checks the POST request and checks that

Sending != receiving. That's not duplicate code, it's just different functionality.

> (and there'd be subtle differences in the variable format between the JSON & regular HTML POST data)

I don't see why.

> and then maybe the way the UI element would be displayed in JS vs in the server-side HTML is also different.

Why would you do that? Inconsistent UI is bad. I'd expect the same UI whether I got the page via URL or via AJAX.

What JS code sharing gives you is the same server-side and client-side rendering. E.g. you can send fully rendered HTML or just JSON depending on the Accept header, saving on data and full-page refreshes but still having SEO (and not having to wait for client-side to render).

You can also share the same model in both environments (like having the same Book class, which you'd have to code twice in JS and whatever server-side language you use).

[firasd]

Trust me, although I've written a tutorial about this[1], it's not that straightforward to do for a live site :) To put it another way, making the same app work with and without JS isn't made much easier even if you use React server-side rendering. But if you make something like that I'd be happy to check it out (contact info in profile.)

[1] https://medium.com/@firasd/quick-start-tutorial-universal-re...