Meaning of $$ in angular [duplicate]

Question

If $ represents built-in service in Angular, what does this $$ prefix mean ? I was just inspecting the scope in Console and saw $$watchers, $$listeners etc

Answer 1

$$ prefix variable are treated as private variable, the reason behind adding $$ before the variable name is, that will avoid the internal variable conflicts and they wouldn't be exposed for external use.

Like in angular you could find many of them, $$observers, $$watchers, $$childHead, $$childTail, $$ChildScope, etc.