How to deubg/log when writing njs scripts and so on?

[BourneSuper]

hi,

unit version: 1.31.1

i have some questions about scripting:

1. how to deubg
2. how to log variables
3. how to share data between every requests
4. it's complicated to update js_modules already uesd:
   a. delete 'settings' in config b. delete js_modules c. update js_modules d. update config