So you don't use 3rd party packages? Because the moment you use one you don't fully understand it --that comes with time. You can't magically know every nuance about a package before you start using it. I haven't looked at the code at all for momentjs or the internals of Vue, there's still a lot I don't know about their api's but doesn't mean I still don't get value out of using them.
I suppose I could spend much of my day carefully vetting dependencies... but what about dependencies of dependencies?