Unable to make it work from example in README

[pkieltyka]

Getting the error:
Uncaught TypeError: Cannot use 'in' operator to search for 'document' in undefined

any suggestions? I'm using webpack 1.4.13

[jupl]

Can I get a code snippet that causes the error in question?

[jupl]

I'm fixing the README. I bet it's that. Nevermind. Still, a code snippet would be helpful in this particular case due to the error.