Download a file quietly ??

Hi there, I am creating this game in witch I am going to have a list of user created levels that the player can play. Sort of like super meat boys TEH INTERNETs but i want it to update automaticly so my question is how can i download a file in node webkit without the save as dialog appearing?

Thanks for your time.

PS

I would be OK with writing a plugin if it is possible in pure javascript.