How do I find the parent folder the game is in?

I'm making a game for Steam and I need to be able to install DirectX when WebGL doesn't work (so the game doesn't look horrendous).

To do that, I put the DirectX installer in the game's folder, then use Node-Webkit to run it.

However, when the game is running from a different folder than it's used to, how do I get the path to the game's folder so I can just say run "directxinstaller" in the game's directory?

Please help.