By taking https://groups.google.com/forum/#!topic/node-webkit/NxhJ4dO80Gc from the answers, you can not show the window at startup by setting the show parameter in package.json
"window": { "show" false }
And then, as soon as the application loads, you can use
var win = gui.Window.get(); win.show();
to show the window.
However, in combination with the kiosk mode, the behavior is not as good as we would like, at least on a Mac, because drafts or white black and white images are displayed in front of the window.
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