instanceof Object not working

[DoroGi]

Hi, I substituted jest-environment-jsdom with jest-fixed-jsdom, to try it out, and noticed that a couple of simple tests are not passing anymore.

I tracked down the issue to a line in my code that is similar to this:

const isObj = (o) => return (o instanceof Object)

Which with jest-environment-jsdom the function returns true, but with jest-fixed-jsdom return false.
Probably related to jestjs/jest#2549?