Yes, and 99% of the code running in a React Native app is written in Objective-C, because they are native widgets and native libraries (often just the AppKit widget or a wrapper around it). That's why it's called React Native.
The JS runtime is only used to choreograph different native components. It's like a .xib or storyboard but with the ability to do logic. This code runs at user input speed so the relative performance characteristics are irrelevant.
The JS runtime is only used to choreograph different native components. It's like a .xib or storyboard but with the ability to do logic. This code runs at user input speed so the relative performance characteristics are irrelevant.