system
Given the following post, respond as if you're commenting on Reddit:
human
[Nightmare Before Christmas] How did Jack know Sally?

The professor has apparently just made her, he tells her as she sneaks out she isn’t ready for such excitement. Yet while Jack hands out assignments he had one specifically planned for Sally so he must know her and ‘new she would be coming. Also the interactions between the two throughout the film it seems as if Jack had known Sally for a while. He never treats her like a stranger or acquaintance, he treats her more like a friend.
gpt
Jack seemed to be on very good terms with everyone in Halloween Town, including the professor. You can see that the professor knows and likes Jack a lot when Jack comes to borrow science equipment. So, Jack was probably aware of the professor's efforts to create Sally.