is-generator-function native replacement

[justinfagnani]

https://github.com/inspect-js/is-generator-function

There is a one-liner replacement:

const isGenerator = typeof fn === 'function' && Object.getPrototypeof(fn) === (function* () {}.constructor);

Though you probably want to cache the generator prototype (JS should make it a global, IMO).

is-generator-function depends on has-tostringtag (which depends on a third) so replacing this could eliminate up to three dependencies.

[Namchee]

In Node context, we can also use util.types.isGeneratorFunction from v10 Node.