> The page that he browser is hit with has ALL the content pre-rendered (sans CSS) in that first HTTP HTML response, and it behaves like a classical webpage henceforth until the moment that the interactivity bits are being hydrated which is deferred.
That is what Gatsby / Next.js do too. The issue is that deferring the hydration doesn't mean it is neither non-blocking nor quick. Once hydration is triggered, the browser gets blocked until it finishes. Of course, the speed of the process depends on the site and how much content it has. If you are building an e-commerce site, this will tend to be on the side of heavy (just the full menu structure, footers and such will be quite a lot already).
> but also doesn't take ages to become interactive.
The issue is that a regular old website can be interactive almost immediately. If you have a hydration process interactivity is inevitably delayed for any part that does require javascript to function... and also for the parts that don't, because the browser main thread is blocked for a while doing the hydration and won't respond to your inputs until it has finished.
If you don't believe me, open an incognito chrome window without any active extension, go to nuxt's own documentation site [1], run a lighthouse performance evaluation with the default settings (mobile/simulated) and see what scores you get.
In my laptop it is a 33 overall for performance, with 4.1s FCP, 9.2s TTI, 6.1s LCP and a total blocking time of 2.41s.
You can also test from https://web.dev/measure/, where I'm seeing a 57 overall (much better, but not good) with 3.5s FCP, 7.8s TTI, 4.9s LCP and a total blocking time of 500ms.
That is, the creators of this software have built a documentation site (i.e.: mostly text, very little interactivity) that doesn't get good performance scores. This, along with blogs, is the best use-case I can think of for the technology. And it doesn't perform good (according to Google's-defined objective metrics, not mine!).
That is what Gatsby / Next.js do too. The issue is that deferring the hydration doesn't mean it is neither non-blocking nor quick. Once hydration is triggered, the browser gets blocked until it finishes. Of course, the speed of the process depends on the site and how much content it has. If you are building an e-commerce site, this will tend to be on the side of heavy (just the full menu structure, footers and such will be quite a lot already).
> but also doesn't take ages to become interactive.
The issue is that a regular old website can be interactive almost immediately. If you have a hydration process interactivity is inevitably delayed for any part that does require javascript to function... and also for the parts that don't, because the browser main thread is blocked for a while doing the hydration and won't respond to your inputs until it has finished.
If you don't believe me, open an incognito chrome window without any active extension, go to nuxt's own documentation site [1], run a lighthouse performance evaluation with the default settings (mobile/simulated) and see what scores you get.
In my laptop it is a 33 overall for performance, with 4.1s FCP, 9.2s TTI, 6.1s LCP and a total blocking time of 2.41s.
You can also test from https://web.dev/measure/, where I'm seeing a 57 overall (much better, but not good) with 3.5s FCP, 7.8s TTI, 4.9s LCP and a total blocking time of 500ms.
That is, the creators of this software have built a documentation site (i.e.: mostly text, very little interactivity) that doesn't get good performance scores. This, along with blogs, is the best use-case I can think of for the technology. And it doesn't perform good (according to Google's-defined objective metrics, not mine!).
[1] https://nuxtjs.org/guides/get-started/installation