GObject.Double
GObject.Double represents the gdouble type in the GObject type system. You can pass this class object to methods taking a GObject.Type.
A gdouble value is a double-precision floating point number, that is, a normal JS number.
GObject.Double is actually an alias to the JS standard Number constructor, and whenever you want to represent the gdouble type you can pass Number instead.
Creating a new object with new GObject.Double returns a Number object with value 0.
Calling GObject.Double(arg) will coerce the argument to a number.