Prevent code from running on server side (add support for Next.js SSR)

[arielitovsky]

When using this library with Next.js and their Server Side Generation, I ran into an issue where the rendering server will return an error:

ReferenceError: window is not defined

This PR fixes that issue and allows us to skip this code on the server, but continue running on the client side.

[hanayashiki]

we need this

[albertpurnama]

+1, need this!