var event = new Date('December 31, 1975 23:15:30 GMT-3:00');

console.log(event.toUTCString());
// Thu, 01 Jan 1976 02:15:30 GMT

console.log(event.getUTCMonth());
// expected output: 0

event.setUTCMonth(11);

console.log(event.toUTCString());
// expected output: Wed, 01 Dec 1976 02:15:30 GMT