Statistics
Monitor
Run the project, switch to the editor while the project is running and open Debugger > Monitors at the bottom of the editor window.
Scroll down to GodotJS section and check available statistics of the running project. You should see a graph appearing as follows:

Statistics
If you need to know the statistics of the JS environemnt running in the editor, open GodotJS > Statistics at the bottom of the editor window.
You will see a table as follows:
