How do I take a snapshot and save it

I export my game in NW.js for Steam. I need a way to automatically save a snapshot to a specific folder (Desktop/DinoSystem or Documents/DinoSystem).

I succesfully did something similiar with save dialog using js:

"var fs = require('fs');fs['writeFileSync']('" &replace(NodeWebkit.ChosenPath,"\","\\")& "','" &CanvasSnapshot& "'.split(',')[1], {'encoding': 'base64'});"

But now i need it to automatically save the screen in the aforementioned folder! Any hint?

I am not sure JavaScript is allowed to do that (for security reasons).

There is one library, and a few hacks that I found on StackOverflow:

http://stackoverflow.com/questions/1340 ... -save-file