Idle Miner part 2: levels service
Too many indirections:


activate just calls addLevel
addLevel just adds a level


And, at least in the posted code, these functions are not used anywhere else.
Is there a merit in having these functions?
You could remove these functions and replace with the simple code that adds one level. 

These local variables are just noise in the code:


var level = this;



Inside a Level class, if you use this it's perfectly understandable that you're working with a "level", no need for the extra local variable that just makes your code longer for no apparent benefit.

The name deep might be better as depth.