[dwoldrich]

Element.scrollHeight first appeared in the DOM API with IE6 in 2001 as far as I can tell. That browser was the first really modern one, with javascript and CSS that could drive a dynamic layout and they innovated with things like AJAX and vector graphics. The web browser had matured from a document model with live elements to a programmable operating environment.

The API implementation was klunky though, where DOM Elements attached to the DOM became 'live' objects. Reading some of the properties would necessarily require reflowing the page in order to calculate the value. It's interesting to think about all the ways the DOM thread can stall for synchronous API's. The Paul Irish gist is always the top hit when I search:

https://gist.github.com/paulirish/5d52fb081b3570c81e3a

The mouse event ones always get me.

I'm always impressed by how old sins like element.scrollHeight can get papered over with newer API's. You can use ResizeObserver or requestAnimationFrame() to time your reads of the property and hopefully get the reflows for cheap or free.