Gtk.Window.prototype.set_default_geometry

function set_default_geometry(width:Number, height:Number):void {
    // Gjs wrapper for gtk_window_set_default_geometry()
}

Like Gtk.set_default_size, but width and height are interpreted in terms of the base size and increment set with gtk_window_set_geometry_hints.

Since 3.0

width

width in resize increments, or -1 to unset the default width

height

height in resize increments, or -1 to unset the default height