It wasn't called hydration at the time. What I did was rendering an initial state of a document, put a script block inside where the state was rendered as a variable - simply an object, which was then picked up by backbone to get the frontend going.
That gave me a fast startup and a fully SPA-like UX in a traditional multidocument application.
We moved an existing application from traditional serverside baked in the early 2000s to a more modern version, where you had small SPAs so to say.
Unfortunately I left in 2015. So I can't tell how it came out. But a full SPA would only be consequential. 😉
So in a sense we played at the time with such types of concepts already.
Only, that you could now dismiss fully fledged web frameworks and go with Gatsby or vuepres mix and match with APIs living in AWS or on premise.
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