Hi, Does the function working is affected when we call it

Question

Hi, Does the function working is affected when we call it

on app start(app.listen) ? not hooked with any request handlers
The Reason to ask is -
i was calling an function on app.listen it was returning undefined
and when i hooked it with an route/request handlers it was working fine

So my question is why it was not running properly on app start

for more reference you can checkout this answer comment section
https://stackoverflow.com/a/69704240/11633187