"As far as how it utilizes cores in the main UI, that's really up to the underlying javascript engine, which most likely will be single-threaded unless instructed otherwise."

So I haven't looked at the code yet but there are many ways to make a web / JavaScript app feel snappier. There is the basic "do everything async" so you, more frequently, release the thread back to drawing / changing the DOM. Some others including:

- Making sure you got rid of the 300ms delay on mobile devices (http://stackoverflow.com/questions/12238587/eliminate-300ms-...)

- Making use everything is minified, combined and loaded up front to ensure initial loading is quick

- If you're using a front end framework look into whether there exists optimizations for speedup otherwise if you profile and find a lot of time is being spent in the framework you may want to work directly with the native DOM APIs

I won't keep going but I've seen a very small, handful of html / javascript mobile apps that have felt practically native in speed so it's possible. But I certainly agree that when first starting up it's a great way to go. React Native may be another good stepping stone.