Jacob Downs Profile picture
Jul 13, 2018 9 tweets 4 min read Twitter logo Read on Twitter
This just reoccured to me for the nth time, but I really wish browsers would just pass along the layout engines own cached values with Scroll/Resize events, like: scrollPosition[x,y], document[w,h], window[w,h] /cc @ietf @w3c @csswg @webkit @mozilla @MicrosoftEdge
...heck, even just a delta[x,y] would be an improvement.

it would make things like parallaxers & scroll position based triggers so much smoother (like at least 2x instantly), since we wouldn't be causing thrashing when we attempt to re-measure these values every 16ms (or sooner)
ultimately, I'd love to see a mechanism for subscribing to high-frequency property value updates. so that we don't need to request measurements for certain element properties in tight loops. but rather, could just receive them in a callback
RequestAnimation/IdleFrame are helpful, but do not fully suffice to solve this issue. at least in my years of attempts at building the smoothest parallaxers possible. especially with many on the same page simultaneously
Imagine something like window.subscribeToElementPropertyChanges('.my-header-div', ['width','height','scrollTop','scrollLeft','offsetTop','offsetLeft'], myCallbackHandlerFunction)
then, the browser's rendering engine could just inject the values it already has on hand, instead of needing to recalculate it milliseconds later
a step further would be some kind of calc() extension to CSS to enable binding these property values directly between elements. I'm not sure which API approach is _more_ wishful thinking... 🤔
are either of these already a proposed thing?

JS hi-freq property registration seems useful to me.
bypassing JS entirely, and offloading all the math to the browser's rendering engine via CSS might make the most sense.

What do you think?

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