My rationale is that any one of these functions is probably going to be put into a utility function that's documented and named already, and of course tested with some optimizations, in some file somewhere in my code base. If it's useful enough, it'll probably be there. And while I don't often do front end, having these utilities support older versions of browsers or if there exist quirks in certain versions of browsers that render the solution nonviable is just not something I want to spend time caring about. When I did Java, the same articles would come out about Guava and Apache Commons.

One should not be afraid to use battle tested libraries, but don't bring dependencies for no reason.