Probably... something like this:
On canvas shapshot....Browser Execute javascript
"var fs = require('fs');fs['writeFileSync']('" &replace(NWjs.UserFolder&"\Desktop\"&"Screnshot"& ".png","\","\\")& "','" &CanvasSnapshot& "'.split(',')[1], {'encoding': 'base64'});"[/code:2pdl5j18]