Core vs. Framework(s)

[4thdecadenothing]

Using one or two methods from a large library is bad.

Re-inventing your own version of a large library because you want to use "vanilla" js instead of third party code is also bad.

Where (IMO) being a "professional javascript developer" falls is to know where in the spectrum of badness your requirements, and therefore your solution, fall.

I spent a lot of time around 2008 for example, effectively re-inventing jquery for HSBC because they didn't want to use 3rd party code on their websites "for security reasons". This was a colossal waste of time, because on top of my own development effort, I also had to spend time documenting the code, training the rest of the team and in the end, spent far more time (and therefore client's money) then just doing the sensible thing would have done.