Echo JS 0.11.0

I recently started using a popular framework that uses css-in-js and noticed similar performance issues. Like serious runtime performance issues, and I wasn't doing anything crazy, I was rendering a small table with some row action buttons, and my app would freeze. 
I spent a long time trying to understand how to optimise, but discovered most of the work was being doing in react context and style generation.

It made me laugh, because react was developed to work around the inefficiencies in DOM updates (moving more logic to JS, eg vdom diffing) but now we're seeing huge performance issues in runtime JS! 
I've now seen the authors of said framework move away from css-in-js and back to plain css (sass). 

I'm yet to be convinced css-in-js is a good idea.