Actually, IIRC it's the exact same reason as the io.js split. The maintainer of jsdom had changes that weren't being merged into node's VM module.

So jsdom 3.x used a lib called "contextify". When io.js was released and the changes included, node support was dropped. Now node 4.0.0 is out and has those changes, jsdom now works on node again.

It was. The maintainer of jsdom decided to no longer support node after 3.x and made the library throw a condescending exception if you tried to run it with node. The docs were also filled with childish "tm" symbols whenever node was mentioned.

I see things like this all the time and it really puts me off OSS.