Add a "reveal" or "hide" selection based layer mask

maskSelection.jsx

maskSelection("revealSelection");

function maskSelection(maskParameter) {
  // Parameter = "revealSelection" or "hideSelection"
	var s2t = function (s) {
		return app.stringIDToTypeID(s);
	};
	var descriptor = new ActionDescriptor();
	var reference = new ActionReference();
	descriptor.putClass( s2t( "new" ), s2t( "channel" ));
	reference.putEnumerated( s2t( "channel" ), s2t( "channel" ), s2t( "mask" ));
	descriptor.putReference( s2t( "at" ), reference );
	descriptor.putEnumerated( s2t( "using" ), s2t( "userMaskEnabled" ), s2t( maskParameter ));
	executeAction( s2t( "make" ), descriptor, DialogModes.NO );
}