[crabmusket]

This library is a hilarious example of a huge problem with this kind of package. "Number" is in the eye of the beholder. A string containing numeric characters is, in my view, in no useful way "a number". A package that treats it as such just perpetuates weakly-typed nonsense.*

But the broader point is, you can't outsource understanding to a package. There will be places in your code where NaN is a perfectly valid number, or Infinity. And other places where you absolutely need to be sure neither of the above make their way in.

By pretending that a package can capture the universal essence of "numberless", and that this will broadly apply across the entire JS ecosystem (see reported benefits like "different libraries can all rely on is-number instead of rewriting duplicated helper functions!") is naive.

I wrote more about this in a post linked in a top level comment. The is-promise library is another great example.

* Personal pet theory is that the package author would have been embarrassed to publish a 1-line package, so included "numeric strings are numbers" as a fig leaf to justify the package's existence. They should have instead created two new packages, is-actual-number and is-numeric-string, so the implementation of is-number could be nice and clean:

    module.exports = function(n) { return require('is-actual-number')(n) || require('is-numeric-string')(n); }

I can feel the power of webscale coursing through me