I think letting the browser do this kind of caching for you is best in most cases. Developers have used tricks to force browsers to layerize content for many years, and browsers have become better at that over time. Nowadays, it should be fairly simple to isolate complex but unchanging content into its own layer that's cached and composited with the rest of the page instead of being rerendered for each page update.
In Shumway, we do almost all rendering in a Canvas element, so we haven't experimented all that much with DOM-heavy constructs.
As for your last question: I used to work with AS3 on a daily basis in a previous work-life, so I have extensive experience with it. Yes, there are some parts of the language that're very nice. I think that optional static typing is the best of all worlds, for example. The details of AS3's type system leave much to be desired, but the IDE support gained through static typing and the large set of bugs that're far easier to avoid are easily worth it.
Also, declarative classes are, in my opinion much easier to deal with than, e.g., the unstructured alternatives in JS. That's part of why we moved to TypeScript, and I'd argue that it vastly improved the quality of our codebase. I'm very much looking forward to classes in ES6.
Of course there are things that I don't miss about AS3 and regret having to deal with in Shumway. Namespaces are one, E4X the other. Both are good concepts in theory but hugely problematic in practice because of issues in the details.
In Shumway, we do almost all rendering in a Canvas element, so we haven't experimented all that much with DOM-heavy constructs.
As for your last question: I used to work with AS3 on a daily basis in a previous work-life, so I have extensive experience with it. Yes, there are some parts of the language that're very nice. I think that optional static typing is the best of all worlds, for example. The details of AS3's type system leave much to be desired, but the IDE support gained through static typing and the large set of bugs that're far easier to avoid are easily worth it.
Also, declarative classes are, in my opinion much easier to deal with than, e.g., the unstructured alternatives in JS. That's part of why we moved to TypeScript, and I'd argue that it vastly improved the quality of our codebase. I'm very much looking forward to classes in ES6.
Of course there are things that I don't miss about AS3 and regret having to deal with in Shumway. Namespaces are one, E4X the other. Both are good concepts in theory but hugely problematic in practice because of issues in the details.