React was one of the first major front-end frameworks to not only name, but tout its rendering performance. React’s virtual dom is famous for efficiently rendering components—but what happens when those components suddenly don’t feel fast anymore? Where do you look? How do you fix it?

Today I’m going to use real React code and Chrome DevTools to demonstrate powerful new performance tracking features and how you can use them to diagnose slow rendering components.

This new performance tooling has three requirements: