You misread my quote entirely.

If you read further down the article you're referencing (davidwalsh.name/css-js-animation), you'll see an example of how Velocity caches values between consecutively chained calls. THAT is an example of the browser not knowing when to optimize transitions in sync with JS code. Another example from that same article: Caching unit conversion ratios (e.g. px to %, em, etc.) across sibling elements in the same call.

Further, JS animation does not eat up mobile devices. You're conflating concepts.

I know that HN can be a stomping grounds, but there's no need to be rude.