Lack of proper typechecking

[canny]

Current state of the backend code is not type-safe, this causes a lot of issues in the long run.
There's a few APIs relying on session data to fetch data in the database, but there is no type checking implemented to prevent a casting error from mongoose.
Affected files:

• Code that uses db.user.findOne({ userid: req.session.userid }); or similar
  • No typechecking for req.session.userid before this line runs
• Code that uses the checkperms function
  • Did implement type conversion, but parseInt can return NaN. However, the users model expects userid to be a number

https://tovy.canny.io/admin/board/bugs/p/lack-of-proper-typechecking

[canny]

This issue has been linked to a Canny post: Lack of proper typechecking 🎉

[7kayoh]

AR: This issue should be marked as major and should be done before 1.x.x release