If you're really going to do it right, that small function should also be published as npm package (isnumeric) that takes at least 2 other packages (isnumber and isbigint) as dependencies.
Do these guys assemble their application as hundreds (or thousands) of NPM packages containing single functions and then import them together? Because now I actually believe they are capable of it.
And this: https://dev.to/leoat12/the-nodemodules-problem-29dc