For some reason the focus is always on preventing re-rendering if it comes to optimising a React app. I understand that it can be really effective and is often the easy way out, but re-rendering in itself is not costly and I don't really care about it the most of the time.
I am more concerned that the code that runs during a re-render is not rebuilding huge static lists that never change and so. I see that over and over again in React apps. I tend to build a lot of the static stuff in the ComponentWillMount stage to prevent that. Only when already optimised code is getting to slow I start thinking about preventing re-rendering if possible.
My reason for not starting with ShouldComponentUpdate is that you have to be very careful not creating nasty bugs with that like I did some times. If a year later you write some code and it doesn't work for some reason it is painful if you find out after a long search that a stupid child component did not update for some prevention rule you forgot about. I really try hard to avoid premature optimisations.
I am more concerned that the code that runs during a re-render is not rebuilding huge static lists that never change and so. I see that over and over again in React apps. I tend to build a lot of the static stuff in the ComponentWillMount stage to prevent that. Only when already optimised code is getting to slow I start thinking about preventing re-rendering if possible.
My reason for not starting with ShouldComponentUpdate is that you have to be very careful not creating nasty bugs with that like I did some times. If a year later you write some code and it doesn't work for some reason it is painful if you find out after a long search that a stupid child component did not update for some prevention rule you forgot about. I really try hard to avoid premature optimisations.