#PerfTip: If you ask for an element's box size (eg:offsetHeight) in any way, it will cause a re-layout to answer your question.

And as you can imagine, if this is a deeply nested child with a lot of auto/dependent calculations, this can become expensive. Use it wisely

Is there a list of all properties that require re-layout?

I was actually thinking of writing a blog post about this, but my tweet sums it up, if you need a box calc - you'll force reflow

So getBoundingClientRect() also forces reflow? Makes sense once you think about it.