[odensc]

In theory `x instanceof Promise` would work, but the reason for this package is that there are many non-standard Promise implementations in the JS world.

[exogen]

It wouldn't work even if everything were native – see my reply above.

[odensc]

That applies for browsers, yes (though I'd argue is a rare edge-case), but create-react-app is a Node.js application.

[exogen]

create-react-app isn't even using is-promise directly. It's several hops in the dependency graph away.