Minimalist libraries as in the op are generally done out of a fear of libraries, as if libraries take away control from the programmer and make the resulting program lesser. Minimalist libraries in npm arise out of a reverence towards libraries, as if something being implemented in a library is superior to an equivalent homebrewed implementation.
When the OP says a library should ideally have one function, they mean that the one function should do the brunt of the work, but leave any setup and takedown to the caller. When a node lib has a single function, this is because you are expected to import another lib for other purposes (eg left-pad for left padding, right-pad for right padding, rather than a single, generic pad library).
When the OP says a library should ideally have one function, they mean that the one function should do the brunt of the work, but leave any setup and takedown to the caller. When a node lib has a single function, this is because you are expected to import another lib for other purposes (eg left-pad for left padding, right-pad for right padding, rather than a single, generic pad library).